[sdiy] Polymoog Resonator virtual ground

[Michael E Caloroso]

Dave Luce had a reputation is using real convoluted circuits to solve
what was a simple problem.

Ever read Vol 1 of the service manual...?  Not the schematics, I mean
the description of the circuits.

MC

On 8/15/14, rsdio at audiobanshee.com <rsdio at audiobanshee.com> wrote:
> The only real drawback is the loss of ultra-low frequencies. Shifting
> signals to a virtual ground is almost always implemented via capacitive
> coupling at the inputs and outputs. Capacitive coupling means that you have
> a high pass, and can't reach all the way to subsonic frequencies.
>
> I don't see any capacitors on the Input or Output of the Polymoog Resonator,
> so I assume the Polymoog runs everything with a DC offset, and then take
> care of it on the final outputs.
>
> Then again, nearly all audio equipment is capacitively coupled, even when
> there is no virtual ground, and so this drawback is not much of a drawback
> at all - even if it is implemented that way.
>
> Brian Willoughby
> Sound Consulting
>
>
> On Aug 14, 2014, at 10:45 PM, Dan Snazelle wrote:
>> that sounds like a very simple way to do such a thing...any real
>> drawbacks??
>>
>> Sent from my iPhone
>>
>>> On Aug 15, 2014, at 1:40 AM, "Donald Tillman" <don at till.com> wrote:
>>>
>>>
>>>> On Aug 14, 2014, at 10:13 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
>>>>
>>>> I was just looking at some Polymoog Resonator schematics, and noticed
>>>> that
>>>> the virtual ground is not 0V, but is about 5V.  Why?  Does anyone here
>>>> know?
>>>
>>> I don't have the inside scoop or anything...
>>>
>>> But my guess would be that they chose to use CD4000-series CMOS switches,
>>> which have a maximum voltage of 18 V, and chose to string them between
>>> +15 V and ground.  They probably thought it would be easier to bop the
>>> audio up to 5 V than to run the CMOS at +/- 7 V and level-shift all the
>>> logic signals.
>>>
>>> -- Don
>
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