[sdiy] Interpreting PEQ schematic help

[Ben Stuyts]

I was looking at this online image and it shows only two wires connected. So the schematic is probably correct.



Ben

> On 5 Oct 2020, at 17:37, Michael E Caloroso <mec.forumreader at gmail.com> wrote:
> 
> 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 <mailto: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 <mailto:ben at stuyts.nl>>> wrote:
>>>> On 5 Oct 2020, at 05:28, ColinMuirDorward <colindorward at gmail.com <mailto:colindorward at gmail.com>
>>>> <mailto:colindorward at gmail.com <mailto:colindorward at gmail.com>>> wrote:
>>>> 
>>>> Here <http://www225.pair.com/audio/waltzingbear/Schematics/Urei/545.JPG <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/colinmuirdorward/>>
>>> -
>>> <https://www.instagram.com/colinmuirdorward/ <https://www.instagram.com/colinmuirdorward/>>
>>> https://www.instagram.com/ssdp_synthesis/ <https://www.instagram.com/ssdp_synthesis/>
>>> <https://www.instagram.com/ssdp_synthesis/ <https://www.instagram.com/ssdp_synthesis/>>

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