[sdiy] Interpreting PEQ schematic help

[Ben Stuyts]

> On 5 Oct 2020, at 05:28, ColinMuirDorward <colindorward at gmail.com> wrote:
> 
> Here <http://www225.pair.com/audio/waltzingbear/Schematics/Urei/545.JPG> is the schematic for the Urei 545 PEQ. I understand that it's a highpass filter followed by four BP SVFs summed into the dry signal, then a lowpass filter.
> I'm stuck on the in/out switch, though. What's going on here? I know what it's supposed to do, but I don't understand how it works.

The switch connects the output of IC1b directly to the output stage IC7. The output of IC1b is very low impedance and is connected directly to the + input of IC7. Therefor, the processed signal (coming in via R52) is completely attenuated (short circuited you might say) by IC1b’s output.

There might be some bleed but it is attenuated by R52 (10k) over the output impedance of IC1b (extremely low).

Ben

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