Tandberg 3001 2.0

Ok, just in time for Christmas I am announcing that I plan to do a run of the 2.0 Output boards.

They will include all of the fixes noted in the manual, the biggest being:

• Crossed resistors in fixed outputs
• Multipath jack being ever so slightly off
• One resistor trace being on the wrong side of the board.

Enhancements include:

• Silver plating instead of tin/lead
• Fully soldermased and silk screened
• Thickest available copper thicknesses

Order yours now for $75. Purchasers of the 1.0 boards receive $15 off. Sorry it can't be more, but these things are expensive when you are doing small runs.

Cheers!

What DID I get into?

Well, folks, the power supply is fully operational. I wish I could say the same for the tuner.

So long as I'm holding onto the tuning dial, it works great. As soon as I release it, it forgets what station it was last on, and tunes to the highest frequency on the dial.

Also, the presets seem to be broken.

On the plus side, it sounds really great, when I can hold on. :)

So, based on this, I'm going to take it to my favorite Cambridge repair place, Audio Lab to see what Derek can do for me.

Maybe for Christmas.

RTFM!

Man, if only I had Read the Freaking Manual (R.T.F.M.) a couple of weeks ago I would be listening to the Tandberg instead of griping about upgrading it's power supply.

In the schematic for the Tuning System 2, which is where P801 goes to, pin 1 is clearly an OUTPUT to the power supply. That is, the 5.2 Volts gets generated elsewhere.

I could blame Tandberg, but honestly, had I remembered correctly how a PNP transistor worked, it would have been pretty obvious to me that it was. Fortunately on page 26 there is actually an arrow showing which direction the signal here is going.

What this means is that I really am done with the Power Supply rebuild! Yeay!

With a little luck, next weekend I'll actually be listening to this tuner for the first time!

A fully re-worked power supply with Mills wirewound resistors, and Panasonic FM caps, a slew of upgraded transistors, and a brand new output board with Cardas connectors and Vishay/Dale metal film resistors, this truly is going to be a pretty good piece of gear to own for a few years more. :)

The TDA 3001: Where are all the Parts?

The power supply is back together, and seems to be working. The 5V supply seems to have some sort of remote sense feedback circuit built in. I don't quite get it, but it was driving me mad until I spent some time with a breadboard and tried out different options.

I've finally decided that rather than assume it's broken, I'm just going to put it back into the tuner and see what it does. I need to check the voltages at the 15V and 25V supplies anyway. While cleaning the header pins which connect to the output board I noticed they had ALL come loose. That is, the solder connections were broken on all of the pins. It wasn't falling out, but it would have made a terrible connection. A few minutes with my 100W solder gun and everything was back where it was. I then took out the alcohol and toothbrush and scrubbed the board to get rid of excess flux and any other dirt which might have accumulated while it was waiting in a box.

The one thing I need before I can re-assemble the tuner is a package of insulated quick-disconnect, crimp on spades. A quick trip to Radio Shack, and the tuner should come back in a snap.

Then I'll probably have to worry about the backup battery and the preselect buttons.

You know, I'm almost ready to begin thinking about my next project. After taking apart the Rega EAR headphone amp, I'm thinking I should consider making my own. The one thing the EAR did well was provide discrete output transistors. Unfortunately, their potential was mired by the use of an aging op-amp design, and single ended supply. I am sure making the product as inexpensive as possible played a major part in these decisions. In order to get rid of the output caps you need a double ended supply, and your biasing solution gets more complicated in order to keep the DC offset as low as possible.

So, maybe next I'll make a headphone amp with high quality op-amp front end, with a Class-A discrete output section. I think I may take apart the InnerSound Electrostatic amplifier I have (manuractured by CODA) and try to use their transistors in my design. Yes, it's ridiculous. but that amp sounds soooo good and it's sooo efficient, that at the voltages we need for headphones they may work really well. Instead of 30 devices per output channel I'll use 2 though. But for this semester, this tuner really is all I'm going to be doing. I have a GPA to maintain. :)

Pics will be coming as I begin the re-assmbly process.

An Afternoon with the Tandberg 3001 Supply

Rather than try a bunch of things and have then be wrong, I ordered lots of spare transistors of the one's I could order, and I spent most of the afternoon today looking for the bad one in the 25V supply.

After replacing a host of little transistors I finally found the one that was causing the problems. The supply is 95% done. The critical 15V and 25V supplies are working perfectly. It wasn't a complete waste of time though, a lot of the transistors were being upgraded to 65V parts, which will make this unit much more stable should I ever have to remove it and modify it on the bench again.

Unfortunately, I'm still having serious problems with the two 5V supplies though. Let me share with you my current (haha!) problems. Take a look at the relevant part of the schematic:



To the left of the 33 Ohm/4W resistor is 15 Volts, as it should be. The problem I'm having is that the two transistors you see here should be outputting 5 and 5.2 V respectively. However, there is too much of a voltage drop through R822, leaving me with something like 2.8 V instead of the 5.9 I should expect. The problem seems to be the current draw through Q814(Q813 on the board). The way I see it, in order for the power supply to behave as documented, there should be about 4.1 mA through R827, and about 1.4mA through Q814. Instead, I'm getting 4.8 mA through Q814 alone. What I don't understand is WHY. The parts all seem to be working correctly. If I remove Q813, and replace Q814 with a brand new part, I still have the same problem. I can't get the voltage at the base of Q813 up to 5.9V. And from what I can see, besides actually changing the value of R827 I really don't have a chance. The input voltage remains a rock solid 15.04 volts throughout though.

I've removed the electrolytic, and measured all of the resistors. Everything is measuring what it should.

Suggestions? Is the schematic bogus to start with?

Modding The Rega EAR Headphone Amplifier

Even though I don't think the Rega EAR is worth the purchase new, I decided to put in information for those of you who may already own a Rega EAR and are kind of curious about getting into making your own modifications. This is actually a device that will be simple to mod for a few bucks which can actually yield some serious benefits.

Tools you'll need:

1. Metric Allen wrench set
2. Phillips screwdriver
3. Soldering Iron
4. Solder Wick
5. Solder

You'll need the metric Allen wrench set to remove the front cover. You'll just strip them otherwise, they are on tight.

Take the back plate off. Before you do anything else, measure the space between the top of the board and the case. You'll need this to make sure you don't buy caps which are too tall.

Disclaimer:
If you read instructions on the internet and follow them without accepting responsibility for your actions, or without really knowing what you are doing and hurt yourself, burn down your house, ruin your stereo or go stark raving mad and start attacking your neighbors lawn mower with an ax while naked in the middle of winter, you are a certifiable dufus and should read no further.

If on the other hand you realise that you are taking risks for the functionality of the equipment you are modifying, and your own health and safety, and will take full responsibility for the consequences of your actions and you are not going to try to act like a dufus by blaming the author of this or any other article online, then please continue.

Capacitors
First, a note about how capacitors are measured. There are three mesuarements which are usually important. Capacitance, Voltage and Temperature. Capacitance is the only value which affects how the part works in circuit. Voltage and Temperature affect when the part will fail. If you put a cap in with too small a voltage rating, it will break down very quickly. For this reason, you can increase the voltage and temperature grades on a capacitor relatively safely. On the other hand, going too far over in voltage may cause you to use a part too physically large, which will be more inductive and may not physically fit. For instance, it's ok to replace a 35V Cap with a 50V or 100V cap. There are cases when the manufacturers original parts were rated too low (see my posts on the Tandberg 3001 power supply) in which case a voltage upgrade makes a really good idea. I don't think you'll find this a problem with the Rega.

One thing to be careful of is that electrolytic capacitors have a direction they should be used in or they will fail fast. Observe how they are mounted in the original, look for (+) signs on the silk screen. Make sure the (-) mark on the capacitor goes to the opposite pin.

Take every electrolytic you see, and replace them with Panasonic FM capacitors, available from Digikey. You should leave the values the same except for the the power supply and output caps. The power supply filter caps are the two large caps rated 1,000uF right next to the power supply jack. Buy the largest cap you can fit into their place. If you can fig 1,800uF you should. This isn't just upgrade-itis. This unit has some serious hum, the only way to remove it is going to be to increase the filter capacitance. By putting in low inductance caps, we can also hope to reduce some of the hiss as well.

For the output caps, putting in bigger units will give you better bass, at the expense of increased inductance and less treble. I suggest that since the Pana FM caps are so low in inductance anyway you should upgrade these by 10-20% if they will fit. You should be able to fit a 0.1uF metal poly film cap underneath each output capacitor. Check the case to board spacing first though.

For all other electrolytic caps, match the original uF values. Leave the ceramic and box caps alone.


Fuse
After adding significant capacitance to the power supply you may blow the little fuse near the jack. Ce est le vie. Short the puppy and move on. Ok, no, just kidding. If this problem arises I would seriously do is add a fuse jack to the back of the unit, and wire it to where this thing is. Then try to put the smallest fuse which doesn't fail when you power the unit on. Somewhere around 200mA to 315mA 5x20mm fuse should work.

You can check the on board fuse for failure by testing the AC voltage across it. It should be near 0. If it's the same as the voltage coming from the wall wart, it's blown.

Op-amp
The single chip in the middle of the board towards the back is an NE5532 dual operational amplifier. Rega probably picked this particular op amp because it makes the rest of the circuit incredibly easy. Let me explain. For an op amp, the 5532 has very low output impedance and is able to drive 600 Ohms to +- 10 V easily. This means they can buffer the input and drive the current gain stage directly, without any more parts. In other words, it's the cheapest possible solution they could find and still have a large current gain capability.

Remove it and replace it with a high quality machined IC socket. This single upgrade is going to give you the most amount of fun, because you'll then be able to experiment with a variety of different dual op amps until you find the one that you like best without having to pull out the solder gun each time.

I suggest the first good one to try is an NE5535. It's probably got the closest sound of the NE5532, but with smoother, richer detail, while still being a rather "cold" part. Philips released it as a Class-A biased version of the NE5532, but I don't think they even bothered to use it in their own products very much and it consumed higher power so except for the modifications market it didn't make much of a dent in the market. I believe Walt Jung (Walt, e-mail me if I'm wrong) wrote about this being a marvelous upgrade to the 5532, but I cold be mistaken. Mouser and Digikey no longer carry it but I found some at ICPlus. Keep in mind that the 5535 does not have the current gain capability of the 5532, so if you have very low impedance headphones, this may not be a good choice, however, several Burr Brown

In any event, once you have socketed the op amp you should be able to find a long list or audiophile recommended parts that will fit, including some who make adapter boards so you can use some of the very expensive Burr Brown single op amps in the socket. Being able to hear the effect different op amps have may alone be a reason to mod the EAR. Here is a good resource for op amp replacements: Tangentsoft Op Amp List

Also, take a look at the op amp pins. I believe there are a couple of unused part locations which were meant to be filter caps but are now marked N/C. You can tell because one of the cap pins will connect to pin 4 or pin 8 of the op amp. If this is true, put a 10uF to 22uF Pana FM cap in each. Pin 4 should connect to the capacitors (-) side. Pin 8 to the (+) side.

Final Words
Like I've said, the Rega EAR is not worth purchasing for the sake of upgrading it. If on the other hand you already have it, you want to learn how to do things yourself, and you are happy to spend about $30 in parts in teaching yourself and your ears how different components affect your sound, then you are in an excellent place. Please let me know how your experiments turn out.

Rega EAR Headphone Amplifier, Final Analysis

After taking a close look at the insides (see previous post) and listening to the Rega EAR headphone amplifier for about 3 hours I can finally give you my reader my definitive take on the product.

I tried four different pairs of headphones:

• AKG K 701
• AKG K 240 Studio
• Shure E4C
• Sony MDR-V600
  

and 2 different source components. I compared the EAR to my SUMO Athena non-headphone enabled preamp, as well as to the direct outputs of my Creative Labs Jukebox Zen 2.0. I actually chose the Athena because I knew that it had limited low impedance drive capability. I figured that it would emulate what a poorly designed headphone jack would do to the sound. On the plus side, it's pure class A and has about a 600 Ohm output impedance, which is pretty darn low for a line level amplifier. Still, it should have been blown away by the EAR.

After a few hours of listening, and after looking closely at the insides I can't recommend this product. Either in absolute terms or price / performance wise.

Compared to the Sumo Athena, it adds too little. The only times I could tell it was a better driver for the headphones was with the 29 Ohm E4C's. Compared to the direct outs, it seemed to muddle the sounds and rob bass drums of their midrange strike and impact. With the AKG 701s it seems to get harsh when there are complicated passages with a lot of upper midrange. Overall, it's a noisy piece of gear, which makes sense given the limited filtering done in the power supply. You can't turn it up too much before the hum of the power supply is clearly evident. The Sony MDR-V600s made the noise problem even worse. They are the most sensitive headphones I have and have a lot more treble than the AKGs which made the hiss from the Rega almost unberaable.

My sample even has some weird oscilation going on when you turned the volume up just a bit, which would disapear, but come on, guys. It's not like you don't have anyone in England who can show you how to design a current amplifier stage that won't oscillate. Otherwise I found the sound to be a complete "Why bother?"

My suggestion to would be amp buyers is to give this one a pass, or buy one, then sell the plastic Rega label on the front so you can go through it top to bottom and mod it until it shines. If. Well, never mind. Don't buy it.

The Rega EAR Gutted!

Last weekend after finishing a mid-term early, I decided to reward myself with a new headphone amplifier. I'd been using this as my primary listening station:



What you see are a pair of AKG K240 600 Ohm headphones. Why 600 Ohms? Because I'm driving them directly from the James Bonjiorno designed SUMO Athena preamp. It's a Class A design with tremendously low output impedance. Certainly low enough to drive these headphones, but it does get noisy if I turn up the gain as much as I need to.

I wanted a headphone amp so I could get gain and power, and free up some desk space. The Rega EAR is less than half the width of my preamp, and fits nicely in a cubby in the desk.

After getting the EAR home, the first thing I did, which was probably a mistake, was take it apart so I could look at the guts. In large part because no magazine review I'd seen had shown us the insides. And now I know why. Tis a sad thing indeed. I am hesitant to even show you but since I know thats why you come here, I'll give you the full naked view first:

From what I can see, you could make something better with about $40 worth of parts. $45 if you include the wall wart. Throw in another $40 and you could have top quality jacks.

The inadequacies with the price/value of this product begin in the power supply. It is single ended power supply, with a single voltage regulator. Remember this, because this is going to cause us problems in the audio section design, which we will cover later.

All of the electrolytic caps are standard grade Korean made Samwha capacitors. By the way, nothing wrong with Korean products. Especially their shoes! My complaint is that they are very standard grade parts, and that by using the simplest possible power supply design you end up having to route your output signal through capacitors before feeding your cans.

Another sad parts about this product is the single input buffer and possibly voltage gain stage. Rega chose to use a single op amp, the NE5532. It's a fine Op Amp. Phillips used to put them in their top of the line CD players, circa 1989. Come on fellows, it's 2006, almost 2007. Would it have killed you to at least use the class A biased NE5535 instead, or any of the superior Burr Brown or Analog Devices products out there today? And how about two of them so you minimize the crosstalk between them?

The one bit of good news is the discrete output stage. Unfortunately whatever good this does for us is undone by the power supply. Because it's a single ended supply, this means that there must be output capacitors. And there are. Two big electrolytics, which are NOT bypassed. That's right. No bypassing. Just straight through. Are they kidding me? No, seriously, an NE5532 and tin can electrolytic output caps? Are they bleeping kidding me?

The last problem I had was that the circuit board is single sided. There's nothing wrong with this, in general, but when you use a single sided circuit board you end up sacrificing the cleanness of the copper layout in order to save a few bucks in the board manufacture. This tends to affect the critical ground and power planes the most. Also, this is a dirt cheap thing to change.

If you can get this thing cheap, it may be a good started uprgrade project for some one. Rip out the electrolytics and replace them all with Panasonic FM. Bypass the output caps, and socket the Op Amp so you can experiment with a variety of op amps.


I did get a chance to audition the Rega EAR at the store with an AKG 701, and compare it to a pair of 600 Ohm AKG 240s. In my opinion, the AKG 701's started to sound compressed and tired when music got complicated and loud.

Over the rest of the week I'll start actually listening to this thing in my system. And maybe after that I'll start discussing the upgrades. But seriously, it's almost a sad thing to NOT upgrade this thing.

Based purely on the parts they put into this product, I have to say, you are better off saving your money and getting something like the HeadRoom Micro Amp for $299. It has seriously better parts value than this... throw back to the days of early mass market Japanese components.

Sorry Rega, I think that this is an exorbitant amount of money to charge people for what you are giving them. Get rid of the extruded aluminum exterior, and take the money you'd save on it and put it towards some decent grade components.

By this Thanksgiving weekend I'll have my actual listening tests concluded and will publish the results.

Coming up Next: The Rega EAR

Gentle Reader,

I have purchased a Rega EAR headphone amplifier for use in my ever evolving home office system. It's gotten great reviews among the head can users plus I got it at a steep discount for being sitting too long as the demo unit at a local headphone store. Don't let that fool you though, most of the other one's disapeared quickly.

Over the next few days I'll be evaluating it against my reference standard headphone amp, a vintage Sumo Athena, as well as the direct outputs of my Creative Zen 2.0 driving my AKG 240 600 Ohm cans as well as the Shure E4C's.

I have to tell you, construction wise, I think it's very little product for the money. $299 new is a lot of change to put down on a circuit board with so few parts, that uses an off the shelf wall wart as it's primary supply. I'll be posting pictures of the insides, and recommended upgrades as I go along, if I think it's worth it.

Cheers!

Man, Just how many Transistors Can you Replace?

It's been hard going here folks. The 25V supply is not showing me any love, but I am getting closer. The most likely problem I'm having is the darlington arrangement. The T0-92 which drives the TO-220 shorted, and at some point the brand new 6.8V zener I put in also smoked.

I have found upgrades for most of the NPN and PNP transistors used, usually just an improvement in the voltage rating. This may not sound like anything useful, but actually, since I don't have a load on the power supply, the voltage after the bridge rectifiers is unusually hot. Higher voltage transistors, and a higher wattage zener will help me keep the thing alive longer until I can put it back into the tuner.

After this, it's back to the 5V supply. Which is basically where I was a month ago. :))

Beware the Lurkers!

One thing I've come to find out about you, dear readers, is that when my blog posts positive things, I get a lot of requests for more information, maybe even some custom mods. But when I post that I've just smoked a resistor, people who were previously sending me e-mails suddenly pretend they don't know me.

So from now on, it's nothing but good stories! About how wonderful the tuner sounds now that I've modded it, and how incredibly sexy the insides and outsides look, and how the mods I have made to my Conrad Johnson PV-10/Erik surpass all tube preamps, ever. All lies, of course, since the tuner isn't even working, and the PV-Erik sounds good, but not better than the good folks at CJ do on their better days, but come on, what do you want? Endless florid reviews that amazingly all say that every single piece of equipment I listen to is priced exactly what it is worth? Don't you get enough of that from the audiophile rags? Well, OK then, I can write like that too, and from now on, I will.

Psych!! Haha! This is not one of those sites I'm afraid. This blog is for the Solder Slapping Adventurer! The Geek who wields his iron like a light saber, striking fear into the hearts of tweak peddlers, gullible consumers, and sometimes our own children and spouses. We are not made of fearful stuff, for we are warriors and we undestand that the feeling of a 500V capacitor discharging through our fingers then down the left side of our rib cage to grab the pericardium so hard we can feel it's entire circumference around our hearts is to be knighted by Thor himself! Now raise your temperature controlled soldering iron into the heart of the storm above your heads, into the toxic fumes of evaporated rosin and scream your defiant battle cry:

Mod-it!

Mod-IT!!

MOD-IT!!!

NPN's, aren't they all the same???

Well, kind of sort of. :) I think I found a temporary solution to my blown transistors issue, an MPS A42 which thank goodness does not have a center collector. It's also a 300V part, but what the heck, I'll take whatever I can. The gain is close to the originals.

This may all be moot, as I have wasted most of the weekend and haven't really studied. I really wanted to listen to my tuner before the end of the week. Guess it will have to wait.

Honey, what's that smell?

"Um, nothing dear.........."

I replied, pulling the power cord on the power supply I was trying to revive.

I had the power supply 90% operational, the only thing I was having issues with was too little on the 5V supply. So, I was re-checking the the voltages using little pieces of wire in the Molex jacks, when I accidentally shorted the 25V supply go ground. Urgh!! !

That smell which wasn't really there was the bouquet of a young 5 watt Mills resister starting to melt it's protective cover.

Now, the PS is 30% operational. I have 15V, but no 25V or 5V coming out of this thing. I could probably get it working again with some generic replacements, but for some reason I don't have a single NPN transistor in a TO-92 case in the house. I guess it's time to order from Mouser again, and I might as well order more power resistors from Parts Exchange, if I'm going to be smoking what I have.

I can't find a source for the BD 419. I can find close matches, but most of the modern replacements have a center collector, which make them hard to retrofit. At this point I feel lucky just to have found the general specs for it. In case anyone can help find a replacment I am looking for:

• Pins: EBC
  
• Power: 2W
• Hfe: 60
• Vce 100
• Through hole, so TO-220 or TO-202

On the other hand this may be a sign from Eutectic, the God of Solder, to design a new power supply board. I may very well end up with the single most expensive Tandberg 3001 ever. :)

More later!

The Long Way Home

Gentle Reader (and I do mean singular!),

I'm happy to say that the power supply rebuild has all but finished. Let me walk you through the pictures. First, is a picture of the original, unadulterated board.

Notice the large cap in the middle next to the transformer? If it was a can of beans you would have had to throw it out for having expanded beyond it's size. My work was cut out for me.

Replace every electrolytic capacitor and every cement resistor. First job was to remove every single part. Leaving me with a very naked board, like this one.

I removed the two main transistors and their heat sinks so I could take better measurements of the circuit board and the holes underneath.

After removing all the parts, I like to add parts back based on the height of the parts. The smallest parts, or those which are closest to the board go in first, then I move my way vertically. This basically meant that the 22uF capacitors went in first, then the power resistors, and then the big filter caps next to the tranformer.

I know it makes me seem old-school to say this, but I really am amazed at how much smaller and better components are today than they were just 10 years ago. Let me show you the finished board to explain.


Look at just how small the caps are compared to the originals. Also, see those tiny black resistors? Believe it or not, they are 5 Watt Mills non-inductive wirewound. You can't get any quieter than this friends, and they are tiny compared to the cement resistors they replace.

You might notice the canary yellow trim-pots which have suddenly apeared too. These are definitely a nice upgrade. The originals were open, carbon composites. These are sealed conductive plastic trim pots. Smooth as honey, electrically quiet, and have much better long term reliability and stability than the originals. Unfortunately one thing I did find when I put everything back together is that the 5V outputs were far too low, which I think is due to a bad transistor. Not a huge deal, but it means the tuner won't be put back together this weekend.

Mid-Terms are Over, Mostly..

Which means, I can take a little break from the world of academics and focus on the power supply. Mikel at the FM Tuner Group suggested I should upgrade one cap to an 80V or better unit, which is on order, but everything else I think I need I have, so Saturday I begin the overaul, and perhaps begin the mechanical drawings on a PS upgrade.

You know, many people whose opinion I respect say that the power supply in the 3001/A is very good, and I mostly agree, but it's not what I would call spectacular. In particular, you have a situation where all of the filter and storage capacitors are on high impedance paths away from the voltage regulation stages. The voltage regulators are kind of live and let live when it comes to all of the different boards they supply. Each board contributes a portion of the overall filtering, but electrically each board is far from the regulators, so sags in the main regulators may take unnecessarily long periods of time to correct. It's all very touchy-feely. Each board can affect all the other boards to some extent.

So, my research is going to be in creating a daughter board to allow the regulator transistors to dominate the output voltages, letting the filtering on the individual boards relax and no longer worry about what the other boards are doing to the supply, and shorten the effective distance between the regulators and the boards themselves. Maybe. I only sold a few of the output boards, so if I do this next step it will be a one off. The good news is that from my initial research I can do it all in a non-destructive manner. I think. Well.....

Digital Camera Cases

Since my GF has adopted my old digital camera, I bought a new one, and then I went out shopping for a camera cover for it.

I have come to the conclusion that there really is no such thing as a good one.

I bought a Tamrac Neo, which I guess means it's made of neoprene, that stretchy fabric they use in wet suites. I have to tell you all, that it's not designed to protect the camera from anything but dust, scratches and mild finger taps. There is no real cushioning in the case at all. It's just stretchy fabric. I also bought a little case for my Pentax Optio. It fell off the strap of my back pack as I was walking to the train, and it has never been the same since. There was almost no padding in that one either.

So, seriously, Tamrac, what are you, and all your competitors thinking? I can't beleive that it's all that difficult to put some foam, something, anything mroe in these cases. Even shock absorbing jell.

On top of all this, the neo case is actually made much bigger than it needs to be by the ultra wide back which the neoprene is sewn onto. I can but hope that some industrious Chinese textile mill will read this and start producing genuinely protective portable case for digitals.

Connector Porn

First, a little tease with the shrouds fitted over the jacks, enlarged slightly to fit the threads. The cross resistor is a fix to a problem in the Rev 1.0 boards, which is fixed in 2.0.







Second, a coy shot from the side with the shrouds removed for your viewing fancy.

Naked Cardas jacks, Vishay Dale Resistors and all the other parts an audiophile needs to listen to ensure his listening satisfaction.

Isn't that a lovely thing? Beautiful high performance jacks reflected in a pool of plated copper. Makes the electrons weep to be still.







Lastly, a sadly out of focus picture from behind, the burn marks proof of a poorly trained and inexperienced solder monkey trying to fix a mis- aligned jack.

You really must be sure you put the jacks in straight, because desoldering them after is insanely difficult. I almost gave up and took the board apart.

Real Pics!

Finally, I have pics to show you, my faithful reader (singular, hah!) Take a look at what it looks like installed in the back of my 3001. The missing screws below the switch is because I lost it. The board fit perfectly. More pics shortly. 

It's Your Turn Now

I realise that in part my postings are kind of rambling in lieu of people talking back to me. I haven't gotten a single comment here about the upgrade boards. I have 6 people on e-bay watching to see if the boards will sell, one e-mail asking for 2.0 boards, but no one else really talking to me about what they would like to see, or whether they like the idea or not.

So, if you are reading this blog with interest, please, drop me a comment, tell me what you like, what you are thinking, what you are working on. Are you wanting the 2.0 boards, but want to see if other's will commit first? Do you wonder if modding this venerable tuner is worth the effort now, or are you busy with school and work so you want to upgrade, but not now? What's goin gon?

Thanks!

Reviews are coming? Maybe.

I got a little good news yesterday, a Tandberg owner has asked me to sell two output boards to him to be installed by a well known FM tuner guy. I'm hoping that I can get some feedback from him which I can use to improve any mistakes I haven't caught, as well as encourage other's to purchase the remaining 2 boards or give me reason to make the 2.0 run.

I've also been doodling a PS daughter-card design. I am pretty sure I'll be able to do the PS mod board. It will be either a tweaker's delight, or a perfectionists heaven, adding a great deal of bottom end to the sound, and maybe reduce overal tuner noise, as well as making the PS incredibly reliable, especially with the early models.

Tandberg PS - Fantasy Land

Ok, I take it back. There are some major upgrades I would do to the power supply if money were no object:

• Double the output transistors used for the 25V and the 15V outputs. This means Q805 and Q811. I haven't done all the math yet, but I think I should be able to keep the original design, without having to entirely redesign the section before.
  
• Add around 600uF of storage right before these transistors.
  
• Possibly add around 250uF of storage after them.
  

The benefits would be:

• Cut the power dissipation in half for each transistor,
  
• Adding significant heat sink radiating area,
  
• Decreasing the output impedance of the power supply
  
• Huge increase in the dynamic current output of this stage.

Having the 1000uF storage cap 1R2 away from the output transistors is just sad. And having no capacitance on the output is also kind of sad. Admitedly, the boards that this goes to all have their own filtering, but at least some polyester film caps on the outputs, if not some more serious filtering would not kill anyone. I'm really kind of impressed that this tuner achieved what it did with such limited power supply capacitance, but this explains a lot of the inductors being used as power supply filters as well.

"But isn't this overkill?" the weak would ask, and we'd say "hell yes!"

Perhaps there is a way to do this with the original, without throwing out the original, either by modding the existing board, or perhaps creating a small upgrade board like I did with the PV-Erik, allowing you to retrofit it. Hmmmmm, I'll think about this as I'm removing caps.

Doh, yes, of course you can buy them assembled!

Sorry for being so dense. I have spent so much time reading around at the FM Tuner Info Site I really thought most people with these tuners would be hobbyists like me, with too many parts and solder lying around, but I realised that many of the people who enjoy listening to the sexiest tuners in the world (Tandbergs of course!) may not be the solder monkey that I am. So, yes, you can buy the fully assembled boards. I will still need the original for the de-emphasis switch, but all the other parts are orderable. So, if you want to upgrade your tuner outputs but are afraid of doing anything more complicated than removing some panel screws and pulling an IC out of it's socket, no problem.

Prices still to be determined, but not cheap, the Cardas jacks are $10 a piece, plus the board, plus the connectors, and of course labor which is distracting me from school and a girlfriend who want to know how it is I say I am broke, but can somehow afford to purchase the last two boxes of hand made NOS carbon film resistors found in an abandonded Shinto Shrine in a mountain of Yokohama which are still so slightly radioactive that they must be smuggled into the country hidden in 100lb cases of marijuana to avoid alerting Homeland Security.

Am I the only one with these problems??

I'll pull out your heart you filthy bastard!

This is what I get for watching Venture Brothers before typing. :)

Ok, it's not a bastard, and it's not it's heart but the power supply. For the next stage of the rebuild I've pulled the power supply completely out of the case. This will let me get to all the parts, and test it without risking the rest of the unit.

I plan the following upgrades:

• Replace all cement resistors with Mills Wire-wound low inductance 5 watts. This is a significant wattage upgrade as well.
  
• Replace every electrolytic cap. If the voltage required is 50 or less, use Panasonic FM, otherwise FC. Bypass critical caps under the board.
  
• Replace carbon open frame trim pots with either ceramic or conductive plastic closed frame both of which are quieter and more stable. The conductive plastic pots are better, but lower wattage. I'll have to investigate why one of the originals got cooked before I can commit to them.
  

This is also a board which could benefit from an upgrade, but I don't think there's enough interest out there. It would be significantly more expensive than the output boads which I don't think I'll sell enough of the prototypes, let alone any production runs. But, if I can use this blog to fantasize a little, I would:

• Size the footprints for Panasonic FM caps, Mills 12 Watt power resistors
  
• Use double sided, 2.5 oz. silver plated boards
  
• Improve the tuner's cooling by:
  
• Using much better, taller heat sinks closer in design to what I used in the PV-Erik. The downside of these is that their footprint is huge by comparison, which is another reason why the double sided baord and smaller parts elswhere will be important.
  
• Add more vent holes directly under the heat sink fins
• Add TO-220 heat sinks to a few of the smaller transistors. This will make warm up a little longer, but greatly improve reliability. They will probably never fail due to heat stress again.
  
• For each 1,000uF cap I would use two 500uF-600uF caps to get lower inductance while keeping the same or slightly higher storage
• Add metal film bypass caps on all the critical electrolytics.
  
• Use the best modern ultra-fast recovery diodes for the bridge rectifiers.
  
• Improve the traces by:
• More than doubling the copper weight
• Thicker, better traces.
  
• Huge power and ground planes
  

If I could get enough orders, I would probably be serious about it, but the bare board would probably run around $400, so for now, I will just start replacing parts as I take a break from school. Maybe by Christmas I'll actually be listening to NPR. Or sending the 3001 to a tuner expert who can get the RF portions tuned up. Or I'll start replacing all the other electrolytics in the system. More likely I'll be trying to catch up because I was soldering instead of studying. :)

I'll post more if I get another digital camera, or after I have done the PS uprgrade.

Take care!

It all fits, and looks great!

It is a real real shame that my Pentax E-10 is now sitting in the garbage can, because otherwise I would have a bunch of pictures to show you, including the fully assembled board, in the tuner. :)

And I have to tell you that from the outside and inside, it is a thing of beauty.

On the outside, with the original shrouds installed over the jacks, it looks very cool. The board connectors with the power supply and the mainboard jumper fit as if they were made for each other. :)

The de-emphasis switch, the standoffs, the audio jacks all are in exactly the right place. Also, the way the Cardas jacks are mounted to the board itself, they feel a lot more sturdy when connecting a cable to them. The one tiny issue in assembly is the cross-resistor I put on the back, to correct for the swap I did. It needs to be right up to the board to best avoid the PS board. Also, I found that trying to raise it from the board just makes it prone to being bent as I work on the front. Best to raise the crossed resistor on the component side if you want to minimize cross talk.

There's something really magical about Radio Shack Soldering irons...

in that every one I've ever used needed to have the tips tightened.

Which means, that I was wrong about the size of soldering iron you needed for the jacks. The 100 Watt soldering gun from Radio Shack works just fine if you make sure the tip is on tight.

I'm looking at my first board, it's gorgeous. :) The tin plating really complements the Cardas jacks, and quite by accident, the metal film cap and the Vishay/Dale metal film resistors go together really well too. I'll try borrowing a camera over the next week so you can see what I'm talking about.

For now, I must clean up my desk, put all the parts away, and start studying. Wish me luck!

Audiogon

I'm happy to say that I actually have two other Tandberg fans interested in the boards so far. Please see my Audiogon listing for sales details.

Maybe I can convince my S.O. that this really isn't the reason we can't buy a house after all. :)

Board Pics!

Ok, so it's not nearly as nice as a real picture, but the scans are not bad either. The boards really look much better than that, especially when you can see the shiny tin plating.

Output Board, Initial Review

Here's the bad news. My digital Pentax has given up the ghost. I dropped it in Boston and it's been barely alive ever since. It's now officially unusable. This means no assembly pics, but I may do some scans of the board.

I've de-populated the original (i.e. ruined) as fast as I could, and compared the two boards.

Here's the objective review:

The prototype is really really good. The multipath output needs to move about a third of a millimeter. Otherwise mechanically it's a really good match for the original. Not only that, it's really a beautiful piece of copper, tin and fiberglass. It's not perfect though. Here are the issues I've found so far:

• The fixed L and R outputs. Fortunately you can cross the resistors that go to them very easily.
  
• One of the scope outputs has the last trace on the wrong side. Fixable with electrical tape.
  
• The holes for the switch are really really tight. I had to use a pair of Robo Grips to finish seating them. I probably could have avoided using solder. :)
  
• I broke the capacitor. I'm replacing it with a 0.1uF metal film. I hope that's good enough! :) It's the right physical size anyway. :) The original one says 250 one one line and then underneath it u 1.
  

These are not show stopper issues, specially if you weren't going to use the scope outputs.

The one show stopper I do have is that the 100 watt soldering gun I have doesn't come even close to putting out enough heat to solder on the Cardas jacks. Tomorrow I'm off to Radio Shack for a 150/250 watt soldering iron. If that doesn't work, I'm screwed, because I am not about to buy a solder pot for this thing!

I'm making fixes to the design, but I am only going to make another run if there is significant interest. Otherwise, this run of six boards is all there will be.

The Wick and Me...

I have prototype boards! Because these are in fact prototypes, I have to take some different steps than hopefully anyone else will. In order to properly guage any differences between the prototype and the original, I have to completely de-populate the original, removing every single part so I can take the two empty boards and put one over the other to accurately see at any differences in the two. Those of you who purchase any of these will be able to get by with just pulling off the Molex connectors, switch and cap.

I have eye-balled them so far and they look really really good. There may be some slight variations in the scope outputs which I will have to correct, but so far, if all you wanted was audio outs, it looks pretty good. :)

Oh, and the Cardas connectors fit MARVELOUSLY! :) I'm very very happy with the way they snap in.


Erik

Prototyping...

The board design is off to the factory, should have it back by Friday.

I'm happy to say that some major improvements were made before it was submitted. The ground plane was broken into 2 sections, one for the audio and one for the multipath and scope outputs.

The traces and resistor locations were optimized even more, giving the fixed outputs the shortest, most isolated trace paths possible. The VARIABEL [sic, "inside" joke, which is itself a bad pun] outputs also have very good trace routing, but maybe a tiny bit less optimal.

The original board kept clearances of about 0.050" around the audio signal traces, this board will have 0.100" clearances, significantly shorter traces, as well as a massive grounds in a star-like configuration. This, along with Cardas jacks (which I understand were originally designed for Jeff Rowland Design) should make this about the best output boards you can put in a Tandberg tuner, short of re-designing how the boards connected to each other. There is also, as I mentioned before, a special feature for multiple cable addicts which I will show you once the boards are back.

The sad part is, I'll probably be selling my extras on e-bay before I ever get to hear the benefits myself. This is because it will be a couple of weeks before the power supply rebuild is complete.

More when the parts start to arrive!

Pics, sort of!

For those of you wondering what the boards I'm making will look like, here is a 3D model created by PCB 123 Layout from Sunstone. The software is among the best that I have used in the free or try before you buy category. It turns out that Sunstone is the parent company for Express PCB, which also has a free PCB layout package. Frankly, it's easier to use, but I went with this one in order to be able to order boards with more features, like 2.5 oz. copper, silver plating, etc.

One of the biggest problems with this software is that it doesn't treat corners as an entity. And that means if you don't like how a trace is routed, you seem to have to delete the whole trace and start from scratch. Oh well, the price I pay for my hobby. Also, please note that the quality of the image is poor, which is based in part on the 3D rendering, and in part on the fact that it's a cut of a screen shot, so don't judge me by the jagged edges. :) 

So where is the progress?

The Tandberg 3001 FM Tuner refurbish project is continuing, sometimes at the expense of my studies, but the output board and the power supply are moving forward.

The Output Board
I received the Cardas output jacks Friday which means I was able to finish laying out the board with accurate device footprints. I will probably order a prototype run of the board this Wednesday, when you may see me selling the extras on E-bay if they fit.

I've also ordered all of the parts for it as well, which is just Vishay Mil-Spec Metal Film ultra low noise resistors. Everything else I will be pulling off the original board.

The Power Supply
When I bought the Tandberg 3001 tuner, I was informed something smoked, and when I took the cover off and found that in the power supply at least one cap had expanded beyond it's normal physical dimensions as well as a carbonized trimmer pot. In addition, I read in a Yahoo FM Tuner group that the power resistors were standard cement types, and sure enough mine were too.

As most of you know, electrolytic caps do have a limited shelf life, and are often the first to go in electronics gear, often taking out other components around them. So for the PS, I ordered abox full of Panasonic FM and FC capacitors, Kiwame Carbon Film and Vishay Metal Oxide resistors, new trimmer pots, and bags full of Panasonic Metal Film caps to use for bypassing. There will probably be a need for new transistors as well, but taking each one out and testing it would not be easy. Instead I will replace all the caps first, and then see if I can diagnose any bad transistors. After this, I will replace the trimmer pots, and power resistors.

Ok, before anyone starts, there is just no space in this thing for the fancy Solen/Auralcap/Multicap bypass caps that are all the rage so don't even start with me. If you aren't going to get hot without those, scroll down and droll at the CJ Power supply mods, then come back to this project. :) Maybe when I start making power supply boards for the 3001 from scratch we can discuss these. :) Just kidding, there's no way I have time for this with work and school. However, if you are a well-heeled devotee of the 3001 and really want a custom built power supply board with some seriously upgraded capabilities and components, send me a note. :) Maybe I can make a bunch of them at once.

Ok, so why not some Black Gate caps? Mostly, they have too long of a burn in time which starts over when you turn the unit off. According to what I read, it takes days for their electrolyte to become fully saturated and for you to get the full BG experience. With a vintage piece of gear like this with notorious overheating problems I just felt that BG's would not be worth the cost of ownership. I'm not going to leave it turned on for more than a day or weekend at a time. Besides, the Panasonic FM's are really really good compared to what was in there originally when this tuner was dominating the FM tuner ratings. Lastly, frankly, I need to see if this tuner ever turns on again. The power supply smoking may have ruined it, in which case spending a couple of hundred bucks on PS caps would be a complete waste.


On Progress and Humility
FYI, this tuner is going to rock when I am done, but honestly, if I had to design this tuner from scratch, there is NO way I could come close to the achievements Mr. Tandberg made to Audio, so I want to take a moment and express my gratitude at being able to in a small way connect with the work he and his engineers did in the 80s.

However, it is also true that many things have changed since then, so it is likely that Mr. Tandberg himself would have made improvements in several areas if he were still around. To begin with, double sided circuit boards are much cheaper in both production and prototype quantities. This is one major reason why I will make the amount of imrpovement in the output board that I will. It's worth going over because much that applies to it can apply to many re-builds of vintage equipment. The original board was single sided, forcing the ground plane had to share space with the audio traces. Because my version is double sided I can put down a massive ground plane on one side, with the signal traces on the other, which gives me better spacing which should lead to lower crosstalk and lower noise than the originals. The other reason this version will be better are the connectors. Rhodium over silver over brass will beat tin over plastic almost every time. As I noted above, I'm using very low noise Vishay resistors on the board as well. Lastly, I'm adding a surprise to the board specifically for that rare breed, the FM and cable junkie. He's not an average audiophile, nor is he an average cable head either. This species of audiophile still tries to find an FM station worth listening to AND he's a cable junkie. A very rare combination, usually found around Boston or LA or Chicago. But I won't say more until the boards are back. :)

The next place where things have gotten better than the Tandberg (and frankly, MY) days is in the size and quality of components. Electrolytic capacitors as well as power resistors have made major improvements in their quality as well as their size. A half watt or 5 watt resistor is much smaller than it used to be. Also, you can find some very high power resistors in metal film versions, which can take 30 watts in the space of a TO-220 case. High power, high stability and low noise in small packages. Sadly I can't use them without redesigning the power supply board (hah!) so I'm going to have to "settle" for some Kiwame's and Metal Oxides. But still, they are SO much smaller than their originals it's almost hard to use them. Two watt 1.2 Ohm Metal Oxide resistors are so small these days it may be difficult to put them in the place where the 2 1/2" long resistor went originally.

Also, we now have the ability to get very low inductance electrolytic capacitors in smaller packages than what Mr. Tandberg used as "standard." I'm talking about the Panasonic FM series here. They are smaller, have something like half the impedance of most other low inductance electrolytics when compared to Nichicon low impedance types. The one bit of a drag is that I can only find them with values up to 50V, so you have to step down to Panasonic FC types to get 63V caps. Not a big deal if you can apply some under-the-board metalized polyester film caps to make up for this small shortcoming.

My point to all of this is that I think if Mr. Tandberg had been succesful, and was still around, I think he would be designing with:

• Double sided boards
• Smaller, higher quaility components which....
• Would let him get enough space for things like metal film resistors with heat sinks, bypass caps, larger ground planes and traces, along with holes in the board for the transistor and resistor heat sinks.
  

One of the things I've noticed about the 3001 is that I don't think I have ever owned a component so full of parts. I think this tuner has more parts than all of my other audio components put together. Putting together this many parts, on so many circuit boards using single sided technology in a low profile design really was an amazing bit of work. If I were to do the industrial design for gear like this I would have used a card cage design, and have made it twice as tall. This is closer to what Revox did during the same era, making their products easy to service but looking a bit like ham radios or toasters by comparison.

When I post again I'll put pictures of the insides of the Tandberg 3001 so you can see what I'm talking about when I say "full of parts."

Maybe I should change the name...

of this blog, because I'm so far away from working on power conditioning that it's almost not funny. Instead I've been busy working on my own mini-system, finding ways to improve it one way or another. I've been looking for a good vintage tuner and DAC to put into my CJ/Sumo/Monitor Audio system, and came across at Tandberg 3001 at Goodwins for $275. Now, if you are any sort of FM fan at all you know that a 3001 doesn't sell for less than $700 anywhere unless there is something wrong with it.

So, I went to Goodwin's and got the answer. Aparently this unit came out of some well heeled accumulator (as opposed to collector) of audio gear. The output board was "cracked" and parts in the power supply "assumed their gaseous state." So, I offered him $200 and walked out with it.

Here is a picture of the output board. It's not really as bad as described. The problem is two fold. It seems like a previous owner used really high pressure connectors and pushed so hard on the RCA jacks that it pulled the tabs and the copper off the PCB on the back. The other problem is that these jacks are just tin and plastic.

So, I am left with a couple of choices, I could scrape off some solder mask, and add big gobs of solder, and stick it back in, and start working on the power supply OR I could make a new PCB board sized for Cardas RCA jacks. Well, if you've followed my blog at all, you know which of these two choices I'm going to take. :)

The mechanical drawing of the original board has been completed, now I'm debating which PCB manufacturer to go with. I like the software that Express PCB offers, but I may want options, like thicker copper traces, or gold plating in case I find others who would like to upgrade their Tandberg 3001 or 3001A boards. 

The Conrad Johnson PV-Erik

Here is another picture, this time from behind, and with all of the wires in place.

There are several major changes. In the front (top of the pic), where the Necromonger heat sink is, the original power supply was upgraded to produce 360V, at 1A if needed.

To the right are the dual mono supplies that take the 360 V and feed each tube 330 independently. Towards the back you can see the red and blue wires (red for Right, of course!) which feed each tube independently, as well as a better picture of the Azuma sockets. I was able to take advantage of unused component holes for these, all I did was enlarge them slightly so I would be able to use enough of the wire to get a solid connection.

The wiring is all Cardas 14 ga. Litz copper wiring. Most of the solder was Cardas, but I admit that some of it, especially for the diodes and resistors, was just Radio Shack silver content solder. I just couldn't wait for the shipment from the Parts Connection to arrive. All resistors are metal film, but not particularly high quality. I did get some Dale/Vishay resistors from Mouser, which were only $0.30 each for the 18k coupling resistor.

The two black wires carry the 360 V from the original regulator stage to the two new stages. There is only one ground wire. This was mostly caused by the fact that I had a really hard time soldering 14 ga. wires with a 40 watt soldering gun. I eventually got the knack of it, but for now, this is how it will have to be. The PCB was designed for this from the start, and will help keep the star grounding method of the original board. 

Recognize Me?

Tell me honestly, it's not that easy to tell that you are looking at the insides of a PV-10 now is it? Some day some one is going to make a living restoring these things, and they are going to open this up and go "what the f****??!!"  

Tubes in a Shroud

While I was ordering parts from the Parts Connexion I also went ahead and got some upgrades for the tubes. What you are looking at are the 12AU7's in Perl tube coolers. In case you are wondering, yes, they really do remove a lot of heat from the tube itself. Whether that will have any benefit at all in the long run, I have no direct experience.

If you look carefully you'll also see the white of the new sockets peeking out. These are Azuma ceramic sockets with gold plated pins. As far as I know, these were the best sockets I could find which could be made to fit. They come with a gold plated pin in the center. Fortunately a little time with a hand drill and they pop right off, leaving the rest of the socket in perfect condition.
Some Tube-o-philes prefer the brown resin sockets which were original with the preamp. They think it's microphonics are the best, and the contacts are good enough. I looked at the contacts, they looked nasty. I'm sorry, they were going. If I every decide to worry about microphonics, that's what the tube coolers will do. 

Droolicious caps!

The boards are now fully assembled, and I managed to figure out a way to mount them that didn't violate the fundamental laws of physics. Take a look! Each board has a pair of 3.9 uF Solens and a single Cardas 0.22uF bypass cap. Also, all the wiring and most of the solder is Cardas as well.  

Conrad Johnson Power Supply Evolution

There's an interesting article over at Stereophile which is mostly about the CT5 preamplifier, but it also talks about how they have moved away from multiple regulation stages as they did in the PV-12 and other preamps, to simplify the design.

I still need the first stage to help drop the voltage, becuase I'm still toying with the idea of removing or reducing the resistor between the two storage caps. Also, by doing it this way, I'm adding more storage capacitance than I would otherwise. I've added nearly 16uF to the overall design, 8uF per channel. That's pretty good at 330V!

Voltage Regulator Schematics

The voltage regulator stages should be familiar to anyone who has worked with Conrad Johnson PV series preamps in the past. The main differences are the output transistor as well as the selection of zener diodes. There is also a difference in the resistor beneath the first diodes, but this value does not seem to be very important. CJ specs 0.15 PS caps for bypass caps which I have been told were made by MultiCap. Frankly, I'm not only running out of room but I wanted to try the Cardas caps in this project, so I'll be using a single 0.22uF Golden Ratio bypass cap across the output filter cap. If I can find enough space for them.

Assembling The Mounting Plate

It's still very much a work in progress, but I figured out how to mount the power supplies without gutting the phono stage layout beneath. I'm going to use a mounting plate to mount the boards on. Take a look below. Tell me, honestly, are you CJ fans out there shocked at the metamorphosis happening? :) More when I actually figure out which order the screws have to go in.  

Pinup shot

In case you are wondering what the boards look like when there are parts in them, here you go. The big Solen and Cardas caps are still missing, which is why the board looks so naked. When they go in you'll see that all the spare real estate disapears.  

It's alive!

Ok, this is just incredibly exciting! :) I assembled all of one board except for the storage caps which are still en-route, used some component leads I had lying around (suddenly I have LOTS of them) for temporary test points, and hooked it up with jumpers to the PV-10s power supply.

Check out the reading on the Fluke next to it, 330 Volts!!! Perfect! Not bad considering I layed out the PCB from scratch, huh?

I'm going to try to finish assembling the other board tonight, and if I have time test it. I probably have another week before the storage caps arrive in the mail, so between now and then I have to figure out a way to mount these boards so that they don't short something and without ruining the underlying phonograph stage layout.

Do you see that large fiberglass "plate" held on by four black screws? Underneath that are all the holes and traces for the phonograph stage. If you had paid another $200 those holes would be filled with the actual parts. For some strange reason, the underlying B+ is still hot. I say strange because Conrad Johnson had to add a jumper in order to make it hot, when they could have just omitted the jumper, and avoided the trouble of putting this cosmetic cover on altogether. Well, who knows what they were thinking. But you'll see how this will work to my advantage in future postings. Stay tuned! 

Honest honey, it's just a few parts...

The first shipment has arrived! Almost all of the non-premium parts have arrived. This means all the diodes, all of the resistors, all the transistors, heat sinks and some mounting hardware and a little metalized film bypass cap. Sorry folks, this is a Panasonic E seriss. I simply could not find a small enough 0.010 cap from any of the premium vendors. They were all too large physically, and way over rated voltage wise. The baby Panasonics are just going to have to be good enough. I will make up for them by adding Cardas in the output caps. Honest!

Even though the main storage caps for this stage won't get here till next week, I can assemble the boards and try them out, to make sure they work, and begin the work of altering the circuit that is on the original.

I'll post more when the soldering iron is hot and I'm ready to start stuffing. 

Building a PV-Erik, or PV-Frankenstein, depending on how you see it.

So, I last wrote that I was fixing a Conrad Johnson PV-10, which was true, but I also wrote that I would be returning to power conditioning, which is only partially true.

Instead of focusing on the power conditioner testing which I had planned, I instead started looking around at the CJ schematics for the PV-10 and 12, and with some helpful ideas from UncleStu at Audio Asulym I decided I would transform my PV-10 into a PV-10 on mega steroids. The challenge is to make it as good of a preamp of it's kind as I could, without actually harming the reasons I fell in love with it in the first place, and I think I have a way of doing this. By leaving the audio circuit 99% untouched, and focusing the work I do on the power supply.

If you scroll down you'll see the insides of a PV-10AL. Notice all that bare space to the right? That's where the phonograph section would normally go if you bought the PV-10A (sans 'L'). In this space I am going to stick two of these circuit boards which you see pictured. They are power supply boards, one for each tube. This will hopefully improve channel separation, power supply regulation, and bass response. They will be chock full of Solen and Cardas Golden Ratio capacitors.

By the way, this is the first PCB I've ever designed for myself. I've designed many, but always for a client or employer. This is the first time I've done one and paid for it out of my own pocket. Pretty nice huh? The design is based on the B+ power supply regulator stages used in the PV-5 through PV-12. It's a little different in that I'm using a TIP50 transistor, which gives me higher breakdown voltages and seriously higher power dissipation than the MJE340s which CJ is so fond of, and seem to blow out so regularly in the preamps this old. So, serious overkill here.

The first batch of parts arrive from DigiKey tomorrow, and then about a week later the fancy caps, jumper wire, etc. arrive from The Parts Connexion.

Stay tuned folks, this really is going to be a major overhaul of the power supply of this preamp, and I'll be documenting all the way.

I think you will see that the mods all stay true to the original circuit philosophy. The only mods I intend to the audio circuit itself are a pair of 0.22uF Cardas caps. Maybe. If I like it. Let's see what the power supply mods do to this baby giant killer first. 

The Johnson Power!

The question itself is: Can I substitute a TIP47 transistor for the MJE340s that Conrad Johnson likes to put in the power supply regulator stages?

Answer: Yes, you can. I tried it, works great. Should consider a TIP48 or better though, the Vce is a little too close to the limit with the TIP47. The TIP50 is even better.

My CJ Preamp is back in business, so my future postings should be a little more on topic, more or less.

Cheers!

Erik

Delays, delays

I know last time I posted I was all gung-ho to get started on the AC probe design. Then a few things happened. First, Bill Whitlock sent me some of the slides he uses to teach a class on power quality and I suddenly had a bunch of questions for him, which I haven't gotten around to ask, especially about balanced/isolation transformers. This was going to be my weekend for reviewing his slides and really getting down to understanding his presentation.

However, instead, my pride and joy, my Conrad Johnson PV-10AL blew a gasket. Not really a gasket, UncleStu at Audio Asulym helped me diagnose the problem. It blew the voltage regulating transistor that fed the 340V filaments (is that the right word? ). With that out, the full 470Volts of the power supply were apearing there, and I was getting massive 120Hz hum on both outputs. If you look at the picture to the right, it's in the middle of the top, attached to the black heat sink.

I spent a little time trying to look for an "upgrade" for the MJE340 which blew. I think I found one, a TIPS47, which has almost the same or better specs. 350 Vce, 1 A maximum current, and a DC current gain of around 30. This gives me 50 more volts and doubles the current capacity of the MJE340, and has the same gain. The negative point is that it has a substantially higher collector current when off (1mA vs. 0.01mA). It's not a concern, because I doubt seriously that it will ever be drawing less than 5mA, and the cut off is 1mA. I also looked around for some heat sinks for the two TO-92s that are on the board. In any case, I bought the "right" kind and the upgrade kind just in case.

I also spent some time at aParts Connexion looking through their 9 pin tube sockets. Next paycheck I'm going to get a pair of the Azuma's to replace the plastic one's. Now, I know that a lot of people think the brown plastic sockets are really the best, but I've looked in the pins and felt the tubes going in and out, and I have to tell you, they just don't look or feel fabulous. The pins on the tubes and the sockets look oxidized, and the feel of inserting tubes is that of scraping rust off the pins as I insert them. So, call me a poseur, if you must, but I'm changing them. :)

One thing to notice about the right side of that picture. See all that bare space? That's where Conrad Johnson would put a phono preamp if you bought the right version. Seems a damn shame to waste all that space, doesn't it? I think I'll have to re-think my comments about not building a headphone amplifier. I think that I could put in either a headphone amp or a USB DAC in there depending on how ambitious I was. Stay tuned!

I hate putting my foot in my mouth....

I wrote that it was "a good thing that Jensen decided not to sponsor me". To be honest, I never really asked them for sponsorship, but did ask if I could get a reduced cost signal transformer from them. After no response from them for a couple of days I figured they decided I was a crank and were going to ignore me.

Instead, yesterday I got a very nice e-mail from Bill Whitlock, president of Jensen Transformers, telling me where my original transformer based designs were screwy, and that I should follow up with their sales group.

Sweet! And don't I feel like a jerk? Sorry Bill!

As an aside, Bill also decided to start ExactPower which I had written favorably before in the articles at PqLtd The two things that I like about their power envelope correction products are high efficiency and massive amounts of power line correction which can be done with it.

Now I'm kind of worried Jensen will send me a pair of their high quality transformers, which of course means that I'd be obligated to use them, and that will mean that I'll have to have a bigger circuit board made. Ah, the fear of success. :)

Schematic V2.0

I decided that before going to production with my circuit board design to find a way to simulate the buffer circuit before hand. I found a shareware product called 5Spice which worked pretty well. I couldn't find a way to zoom in on the schematic, but beggars can't be choosers.

I truly long for the days when I worked for companies that could afford to purchase integrated schematic capture, simulation and PCB layout tools. It would have saved me the trouble of drawing the schematic twice, making my own NE5532 models, and then trying to use different keyboard shortcuts in each. Anyway....

Based on the simulation analysis, I realised that because the voltage divider I was using was single ended, the power line signal shape I was seeing in Visual Analyzer were wrong. The neutral line noise was coming in at 1x while the line signal was 1/10x. Also, I didn't like the band pass characteristics I was seeing. Lastly, I realised that part of my problem was that the input impedance was so high that I was going to get much more noise than any real audio equipment would ever see.

So, with this in mind I redesigned the front end. Now, the input is balanced, the input impedance is reduced to around 55K, and the 115/240VAC switch will instead be used to allow me to short the AC line to ground, so I can see the neutral line noise separately. Don't worry, the input impedance will still be 50k, so no more than 3 mA will flow no matter what I do.

Which brings me to a small point about safety. Originally I did not want to shunt any current at all to ground. I was worried about noise on the ground line affecting my measurments as well as concern if the ground wire sould fail. Either in the case or between the case and the service connection. Also, for many reasons, I wanted the signal ground to float. In part it's because PC's have notoriously bad problems with ground loops. However, with the 50K resistors in place on both sides, the peak current that some one could face is 3mA. You'd can feel 1 mA, but 3mA apears to be safe. To put it in perspective, GFCI breakers installed in your kitchen trip at 10mA. 20mA is conisdered potentially lethal, and 16mA is considered the maximum amount of current that can flow through an adult and still be able to let go of the conductor. So based on all of this, I think it is in fact safe to connect the line and neutral to ground at this point.

Not shown in the schematic are 50mA 5x20mm fuses which will be on the hot and neutral side.

Also, I've changed the arrangement of the TVSS diodes. There are now two, and the'll fire at about 15-20 VAC (depending on which I decide to get, finally). This should ensure that even if a failure of the neutral or ground occur the buffer as well as any connected PC or audio equipment will remain safe. If I had more space, I would instead put in a "muting" cirguit like they use in op-amps and amplifiers so that if the voltage at either input of the buffer were too high it would disconnect, but I just don't have the space, and with 50K of input impedance I don't think anyone will be in danger. If my cat pees on it though, all bets are off, but that would be the case if he peed on my 300w/Ch InnerSound amp as well. So, UL be damned! :)

Why IS my AC so bad?

I've been wondering just why my AC was as bad as it is, so I've been doing some investigation. The THD measurement is around 7% right now. If you look to the right, there's a picture of part of the AC wafeform. The white circle shows a small negative spike. This is caused by the fluorescent lamp on my desktop. The bigger problem however was the severe drop at the top and bottom of each cycle. It's circled in read.



After some experimentation, I discoverd that it is in fact being caused by a spike on the neutral coming from my laptop's power supply. The graph on the right is a graph of the neutral voltage at my desk. In an ideal world, it should be completely flat, and match the voltage at the ground pin but in my case every half cycle my laptop is putting a significant amount of current onto the neutral wire. Because the resistance between my desk and ground is not zero, the current flow causes a voltage spike to occur in the same direction as the incoming line voltage, with the effective result that the voltage between line and neutral dropping, and more noise and less effective power available to your equipment.

If I turn off the lamp and disconnect the laptop these neutral spikes disapear, the AC waveform becomes much cleaner looking and my THD measurements drop to under 3%.

All of this is great news, because it means I have at least two good ways to test the efficacy of any power conditioners that may come my way, especially those with special sockets for "digital" components.

Cheers!

Doh!

I realised as I was going to bed that if I wanted to drive 600 Ohm loads with the NE5532's I couldn't put a 50 kOhm pot in front of it.

So, today I'm experimenting with reversing the last op-amp and the pot. My biggest concern is that the power supply noise that was previously driven down by the 5:1 attenuation in the pot will come back up. If the noise looks low enough, I'll just make this one final change and have the board made. Otherwise I'm going to have to consdider adding more power supply filtering, and perhaps some RF filters on the input to the buffer and final stage.

Stay tuned!

Erik

The Buffer Circuit

In the interests of full disclosure, I'm including the entire buffer circuit here for your perusal. The first section is a voltage divider which brings the 120 VAC down to a reasonable 5 VAC. There is a shunted 1 MOhm resistor there in case I ever want to compare an isolation transformer or balanced power regenerator a'la PS Audio. The jumper there will be connected to the 115/240 VAC selector switch on the back of the gutted power supply case.

There is also a place for a 15 VAC transient supressing diode made by Littelfuse in case I mess something up, I am hoping this will keep me from frying the laptop. After this, there are two 250VAC 0.1uF metal fil caps which couple the input stage to the amplifier buffer stage itself.

The buffer stage consists of NE5532 Op-Amps for several reasons. I have them, they are relatively low noise and low distortion, and they can directly drive a 600 Ohm load. In the circuit board design I was going to switch over to a single quad J-FET op-amp, the TL072, which are low noise but in the breadboard prototype I noticed some odd voltage drops when connecting the buffer to the mic input. This made me worry more about the mic input impedance than before.

Now, in an ideal situation, I would use a transformer of some sort to keep the current on the input side of the buffer from finding a way through ground to the neutral. However, good signal level transformers such as those made by Jensen Transformers are pricey, and I no longer have the room to put one in the board. Good thing they decided not to sponsor me, because I would have had to get a bigger circuit board. :)

The power supply is not shown, but it involves the salvaged bridge rectifier from the PC supply, 4x2,200 uF Panasonic FM caps feeding LM78L15 and LM79L15 voltage regulators, after which are a pair of 4.7uF tantalum caps, and perhaps a pair of 0.1uF metal film caps as well.

The last part of the buffer is a multi-turn pot. The mic input only accepts signals between +- 1 Volt. The buffer circuit is set to a gain of 1. So, becasue of this, the signal must be reduced from 5 Volts RMS on the output of the buffer to less than 1 Volt RMS on the Cardas RCA jack. When using a balanced input, I'll have to turn this back up a little.

The good news is that because there is so much attenuation, what little noise and ripple are in the op-amp outputs they get reduced by a factor of about 5, so I expect that my overall SNR will be quite high. I certainly can't see it in the scope measurements.

Before anyone goes nuts asking me why I didn't use this part or that, remember two things. First, I'm on a very tight budget. Second, I'm looking for relative differnces in performance of power conditioners. The normal THD+N measurement at my desk of the AC line is about 7%. Not 0.7%, but 7%! Probably two orders of magnitude greater than the buffer circuit I'm using. Also, I don't want to accidentally clean up the signal by putting too much in the circuit. The one exception I've made to this are fuses and a TVSS to keep me from frying anything. But the TVSS is off until it's overloaded.

So it Begins

The thing that got me started down this path, again, was finding a cheap way to make circuit boards. I found a place called Express PCB which has a prototyping service that costs $51 + shipping for small boards, along with free schematic and circuit board software. I started playing around with it, and then thought "What can I do with a circuit board that's really useful, and hasn't been done by everybody?" So that eliminated making my own headphone amp, preamp, amplifier, etc.

For a while after I thought of this blog, I was going to give up. I was adding up the parts cost, and it looked like I was going to have to spend $200 or just to get started. Too expensive for a hobby I thought(ok, you with the dual mono-block Jadis amplifier, stop snickering!) Then three things happened all together.

First, I found that many of my needs would be served by this mini-PC power supply. I found it headed to the trash in the building I work at. It was a gold mine in disguise for the thrifty minded solder monkey that I am becoming. It included a grounded case, IEC electrical receptacle, DPST power switch, a 115/240 V switch which could be repurposed to become a balanced/unbalanced switch (more on this later), some existing fasterners for the circuit board, some jumpers and a bridge rectifier and even a plastic sheet on the bottom to lessen the chances of shorting something by accident. The paper you see in the bottom of the case is an ink-jet paper puppet of the future circuit board. By printing the top layer of the circuit board actual size, I can make sure that everything is in the right place before I get the board itself manufactured. You will also notice the heart of my power suppply, a 5 amp center tapped, 30 volt transformer, which will fit nicely in the corner.

The second thing that happened is that this juicy bit-o-kit arrived in the mail, free of charge. Recognize it? It's a Cardas GRFA PRT printed circuit board (PCB) mountable female RCA plug. Usually around $20-$30 each. So, in a way, I had sponsorship. This doesn't mean that Cardas has in any way aproved of my blog, but now I feel obligated to use it, or pay for it. So, now a word about my sponsor. This is the sweetest RCA connector I've ever seen, or felt. The RCA plug sliding into it is absolutely butter smooth, but, the footprint is HUGE! I mean, it's great if you are making a high-end preamp, with a large circuit board and you are already putting in 0.1 uF capacitors the size of a cat's head, but in order to get the prototype discount I have to use a board that is exactly 3.8" x 2.5". This beast is literally the size of most the buffer circuit I am using. Fortunately most of it hangs off the circuit board, but still, it's huge. If you want to use these for production you will have to use tight tolerances between your boards and the case. The space between the ground pins and the start of the threads is only about .150 inches. If you are using round holes, your spacing drops rapidly. So, I can see why the case mounted versions are more popular with DIY'ers. The case mounted versions are just as good, and easier to manage. Leave these to the manufacturers paying the megabucks for the gold plated boards, and +-0.001" case manufacturing.

As an aside, the guys at HeadRoom managed to stick 3 double sockets plus a single in the back of Desktop Headphone Amplifier along with a DAC, amplifier and power supply in their design. That's pretty impressive if you ask me.

The third thing is that I found really cheap PC Oscilloscope software that seemed to work pretty well. I found two good sources, but ended up going with Visual Analyzer because it's frequency counter was more accurate, and it had a built in function generator.

In my next post, the buffer itself. For those of you who want to see exactly what I mean by "easily flammable!"