Question About Gain Stage of Ampeg r212r

[daradaramike3]

Hello again and as always thanks in advance for any help!

Anyway, I was looking at the schematic for an Ampeg r212r Reverberocket (new dual channel model) and have some questions.

At the first gain stage, it looks like if the amp is clean the gain knob is bypassed, some of the signal is shunted to ground via a 10k resistor and what is left is then passed to the next gain stage and on to the tonestack and so on and so forth. (schematic below but displays lead channel path by default)

So here is my first question: I tried to draw it out to help me figure out what is going on and was wondering if the circuit I drew on the bottom part of ampclean.pdf (attached) is the same functionally as what I drew on the top half, if I were to remove the bypassed gain pot and draw the whole thing as if the amp is switched to clean.

My second Question: Also, if you look at the Ampeg schematic, when the amp is set to dirty, the signal that would normally go to ground from volume pot after the tonestack (which controls clean volume) is looped right back into the signal. Does this "virtually" bypass that control by making it useless because of the infinite loop of signal?

Sorry to ask such mind-numbingly basic questions but I just want to make sure I have the right idea as to what is actually happening. Thanks!

Mike

[cbarrow7625]

You got it pretty close. The way you drew the clean channel is about 90% correct. The only thing you missed is that the gain pot turns into a variable series resistor between the top of the 10k resistor & the grid of the tube. While moving the gain pot around while in clean mode you may notice a slight drop off in high frequencies when the pot is at around 8 or 9 o'clock (that is the point on an audio taper pot where there is equal resistance to either end of the pot).

The master volume bypass does the same exact thing as the gain knob bypass; it shorts together the two ends of the pot to bypass it. It just looks more complicated because of the .001 cap wired around the pot - it's just an extra component that adds to the drawing's complexity.

[daradaramike3]

Hi! Thanks for the reply!

That leads me to another question then: Is this even a worthwhile gain stage if there was no dirty channel involved? It doesn't seem like it would be but if I had a clue I wouldn't be asking!

Thanks again and sorry for the onslaught of noob questions.