Marshall ED-1 compressor

[David Schwab]

Someone else at the diystompbox forum redrew it. All I did was save it and post it.

I was wondering.. I looked at it and thought "that doesn't look so bad" lol

[Mark Hammer]

Yeah, all of those Marshall pedal schematics are enough to give you a migraine. There is very little about them that permits an easy understanding of the circuit. Maybe they were meant that way. On the other hand, if you've ever seen any of the circuits from Nicholas Boscorelli's stuff, whether the Stompbox Cookbook or the Stompboxology newsletters, you'll see schematics that were deliberately intended to be instructive (or at least accompany instruction) but are every bit as hard to follow as the Marshall drawings. I guess some folks have a good head for drawing things, and others not so much.

I don't know about you, but my capacity to recognize functional relationships or elements in a circuit can very much depend on the manner in which it is drawn. Sometimes, all it takes is a simple 90-degree rotation of a pot and all of a sudden the lights go on...or off.

[Steve Conner]

Me too. The way that I visualize how circuits work needs things to be arranged on the page roughly according to their voltage, so in a tube amp you have B+ at the top, ground near the bottom, and bias voltage under that. Current flows from the top of the page to the bottom.

And yes, when I try to visualize the AC operation of a circuit, I can't help but see things fly up and down the schematic according to their instantaneous voltage, with diodes flipping head over heels and resistors getting squeezed and stretched like accordions.

As a consequence of this mental model, when I first saw those old Fender schematics that draw one tube of the push-pull pair upside-down, I wondered where in heck they got PNP tubes from. To make sense of the push-pull pair, I have to draw the output transformer horizontally, so the primary is like a see-saw or pair of scales, with the power tubes yanking on the ends to make it "swing".

I actually worried that I might have been one of those "special" kids, till I read an article in an electronics book by a designer who visualized things in just the same way. (The book was edited by Jim Williams, so everything in it must have been right.)