[sdiy] Interpreting PEQ schematic help

[Michael E Caloroso]

That's a pretty strange in/out technique.

Suffice to say, don't put too much faith in schematics as they often
are not 100% accurate.  Errors are known to be intentional to deter
copycats.

MC

On 10/5/20, Ben Stuyts <ben at stuyts.nl> wrote:
> I don’t see any sonic advantages. If the offset voltage on the output of
> IC1B isn’t exactly 0 (set by R63) you will have audible clicks anyway.
>
> As far as I can see from online images, the switch is not on the pcb. So it
> saves one wire to solder/assemble. Maybe it was just for economical
> reasons.
>
> Ben
>
>
>> On 5 Oct 2020, at 16:25, ColinMuirDorward <colindorward at gmail.com> wrote:
>>
>> 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
>> <mailto:ben at stuyts.nl>> wrote:
>>> On 5 Oct 2020, at 05:28, ColinMuirDorward <colindorward at gmail.com
>>> <mailto: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
>>
>>
>>
>> --
>> https://www.instagram.com/colinmuirdorward/
>> <https://www.instagram.com/colinmuirdorward/>
>> -
>>  <https://www.instagram.com/colinmuirdorward/>
>> https://www.instagram.com/ssdp_synthesis/
>> <https://www.instagram.com/ssdp_synthesis/>
>