The Pro-Ject Headphone Amplifier

I'm still looking for good values in headphone amplifiers. As you might recall, I previosly tried the Rega EAR, which was just too expensive and offered too little, and was noisy, so I started looking for something cheap enough that I could leave at work, and maybe give me equal or better value, and maybe be worth modding a little hear and there.

I think I've found it in the Pro-Ject Head Box MKII. The Pro-Ject headphone amplifier has a similar design to the Rega. Meaning, single ended supply, one op-amp driving a discrete amplifier stage. Externally there are two major differences. The price, $99 for the Pro-Ject vs. $299 for the EAR as well as the complete lack of switches on the Head Box. Which I guess makes sense if you are going to put in some BlackGate capacitors that means you'll have to leave the box on all the time anyway. :)

Listening Tests
Right out of the box, the Head Box is significantly quieter than the Rega EAR. I can hear no noise at all except at the loudest setting. It seems to be a little weak on the bass however, and perhaps a little on the treble as well.

Build Quality
The Pro-Ject headphone amp is less expensive than the EAR, but better made, in my opinion. This major difference probably has to do with the power supply filtering. The EAR had about 1,500 uF of filtration, the Head Box around 4,000, with a significant amount of filtration occuring after the voltage regulator.

Just like the EAR, the Pro-Ject amp has to have capacitors at the outputs. They are about half the size of the EAR's so this may account for why I feel the bass just isn't making it all the way through to the headphones.

Future Mods
There are two major areas where you can improve this little box. First is in the capacitors. Replace them all with Panasonic FM's. For the output caps, replace them with 1,000uFs if possible. This should get you some more oomf.

The other area is in the op-amp. There's nothing wrong with the original, but there is nothing great about it either. Socket it and experiment. If you can find an NE5535 to hear what vintage class-A op amps sounded like, I'd recommend it. :)

I'll post as I apply the mods.