Traynor YCV 40 Schematic and circuit Explanation

[JustMike]

First off, this schematic is a different version than the one in the Hoffman library. Prolly a rev, but it's correct to the amp I have.
 So I'm not following how the channel switching is working. It looks like when the drive channel is enabled, the clean channel is still passing thru the tone stack and on to the PI via R23. What am I missing here?


 Also, the B+ circuit is strange. There are 5 Zeners in the B+ line to drop the voltage to 300VDC. I thought this was more a "fix" than good design.
 
 I think I can kind of follow the Opto coupler/Mosfet standby switching, but it seems unnecessarily complicated.

[sluckey]

It looks like when the drive channel is enabled, the clean channel is still passing thru the tone stack and on to the PI via R23. What am I missing here?

You're missing K1-B.

Also, the B+ circuit is strange. There are 5 Zeners in the B+ line to drop the voltage to 300VDC. I thought this was more a "fix" than good design.

That is a typical series pass regulator. Been around since zeners were invented. There's an all tube version that goes back even farther. It's a simple, reliable way to regulate voltage. It's not a band aid fix. However, it appears to be missing 1 zener. To regulate at 300v (actually 306v) you need six zeners at 51v. Five of those zeners will only give you 255V.

I think I can kind of follow the Opto coupler/Mosfet standby switching, but it seems unnecessarily complicated.

They just wanted to show how smart they were.   

[2deaf]

Also, the B+ circuit is strange. There are 5 Zeners in the B+ line to drop the voltage to 300VDC.

It's a regulated capacitance multiplier.  Q10 is configured as an emitter follower, so the voltage on the Emitter is going to be pretty close to the zener-regulated voltage on the Base.  The capacitance on the Base gets multiplied by the gain of the MJE340.  This allows them to use small filter capacitors while getting the performance of huge capacitors.   

[PRR]

...5 Zeners in the B+ line to drop the voltage to 300VDC. I thought this was more a "fix" than good design....

That's dead-standard circuit, over-elaborated. Ask Google.

The stack-of-Zeners is cuz we need 300V and >50V is rare. It looks totally over-capacitored, as if it was more important to work first-board than to Muntz-out every penny.

[JustMike]

It looks like when the drive channel is enabled, the clean channel is still passing thru the tone stack and on to the PI via R23. What am I missing here?

You're missing K1-B.

 So, K1B shunts the clean signal to ground. Got it. What purpose does R23 serve? Is it a buffer? A "pop stopper"?

[sluckey]

Looks like it works with R23 to form a voltage divider, possibly to balance the signal between clean and mean channels.