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Old 27th October 2011, 12:02 AM   #1
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Join Date: Feb 2011
Default Marshall JCM900 2500 preamp

Hi

I am trying to make sense of the preamp for a the marshal JCM900 2500 (http://www.drtube.com/schematics/mar...d0109-iss9.pdf). I have a few questions:

- why the two zeners at the input?
- One leg of c14 is connected to gnd and the other to the top of the input connector through something called "link". Is this link a contact? If not, what is c14 actually doing?
- VR1 is connected to the Cathode of V1b through c15 and to the grid of V1b. What exactly is it doing to the tube? Also, D1 is part of the same circuit. That is operating as a limiter correct?
- Can someone explain to me what kind of feedback C16 creates?
- I read on a bunch of places that Vr2 "bypasses" the rectifier BR1. I am assuming that basically, on its lowest setting it attenuates the signal enough so that the bridge will not clamp it. Is that assumption correct?
- lastly, and i am ashamed to ask this, but what does c6 does to the circuit on V2a?

Thanks all
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