I spoke a little too soon about the Yamaha not having any protection circuitry. Looking through my class handouts/notes from Dr. Leach's lectures, TR12 and TR13 provide current limiting. If either saturates they remove voltage from the base of the drivers, TR14 and TR15.
I stand by my original assessment that the temperature light is a waste of good power best used elsewhere though.
I'm still trying to figure out the extra windings which are used to add about 14V of negative supply, which seems related to the bias and input stages. It's almost as if they are trying to keep the input off center, so it operates linearly, before driving the rest of the amplifier in a more balanced manner.
Ideas?
Biasing was my first thought. Similarly in tube amp design, I have seen some input stages with an additional negative bias to create a constant current sink through transistors or a mosfet. Additionally, I have seen it used to impose negative distortion. Not having the circuit diagram I can't say. Remove the feed and see what happens to the distortion. I do have one of these amps, however. This might just have given me the push to take mine apart. Ive always been tempted to buy two more of these to use as a matched set in my home theater, but felt that it needed a rehab to reach a higher level of potential.
ReplyDeleteFYI, I work in NBPT and have lived there most of my life, although in Haverhill right now.