Hi Terry,
If the cap multiplier is fitted to the FetZilla and the quiescent is only 350mA, then two channels would draw about 720mA at idle and bounce up from there with music signals. I would not expect much heat from the cap multiplier because the total idle dissipation would be 0.72 x 1.5 = 1.08W, almost nothing for a large series pass transistor, maybe an average of about 3W passing heavy music.
Very different to a Class A like the Alpha Nirvana which will be passing and average of 1.7A and up to 4.5V across it. That is 7.65W and you'd really notice that.
The offset issue is a nuisance but based on past experiences with singletons and bipolars, it seems to be caused by the heavy tempco of the jfet input device and mosfet VAS device. Small temp changes there will cause big changes on the offset, and its origin is first and second stages, not the output stage. Understandably this could be improved; but to do it, and improve the depth of image as well, the best way would be replace the mosfet VAS with a bipolar, like a KSA1381. I believe a bipolar is far better for the VAS role; it has much more transconducance and therefore more accuracy than a small mosfet.
Thanks for keeping the thread moving........
Hugh
Hi Hugh,
The offset was weird but I don't think it will cause any grief. I'm just going to forget about it. The speakers won't care. Good to know about the Cap multiplier being sufficient because it is very clean and I think a good option since I cut off the original PSU portion of the boards.
I've added this amp to my A/B stack and am looking forward to comparing it to other amps.