Question about CSR2 Pedal Circuit

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Wisdom Cracker
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Joined: Fri Feb 10, 2017 9:37 am

Question about CSR2 Pedal Circuit

Post by Wisdom Cracker » Fri Feb 10, 2017 9:50 am

Hello.

I'm looking at the circuit for the Peavey CSR2 compressor pedal. Many compressor pedals have a Mystery Box in the schematic, representing maybe a transconductance amplifier or the like. But the CSR2 has two Mystery Boxes, and that's intriguing.

They appear to have only factory numbers on the drawing which is even more mysterious. I suppose that one is a transconductance amplifier because they turn up so often. But what is the other one?

Wisdom Cracker
New Member
Posts: 2
Joined: Fri Feb 10, 2017 9:37 am

Re: Question about CSR2 Pedal Circuit

Post by Wisdom Cracker » Sat Feb 11, 2017 8:38 am

I think I've got it. The chip is one of the ancient 570 series compander, originally invented to reduce noise in transmission and recording chains. It's a two-channel chip. The first box, one side of the 572 in the feedback loop of an op amp, composes a compressor. The second box, the other side, composes an expander.

I don't know how the ingredients are prestidigitated to make the pedal do what it does, but there it is.

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