[sdiy] Interpreting PEQ schematic help

[ColinMuirDorward]

Thanks Ben!
What's the advantage of doing this, rather than using a switch connected to
the output buffer that toggles between either the processed or the
unprocessed signal?
Less click?
Colin


On Mon, Oct 5, 2020 at 12:43 AM Ben Stuyts <ben at stuyts.nl> wrote:

> 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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