[sdiy] Dual/quad opamp bleed-through

[Dave Manley]

Here's another single board dual VCO - the Oberheim SEM

http://www.sequencer.de/pix/oberheim/oberheim_sem_module_m.jpg

The two VCO's are symmetrical and in the upper right of this image.  Voltage
summing at the top, two tempco's on top of a 3086 expo, two polystyrene
timing caps at the bottom (just above the 'de' in "image www.sequencer.de".
No common parts, except the 3086.  Looks like good use of a ground fill
to isolate parts of the two VCOs.

-Dave

> I'm going to play devil's advocate and mention a few well known
> synths that have multiple VCOs on the same board: Moog Mini,
> ARP Odyssey, and KORG MS-20.  They don't share ICs, but
> they are on the same board.
>
> Do any of these synths have unintentional oscillator sync problems?
>
> -Dave
>
>> The first prototype of my dual VCO module had this same problem.
>> I then split the two VCOs onto separate boards with shared panel 
>> controls.
>> This design still had sync problems. It was only after I placed the 
>> boards at least 3/4" apart using standoffs that the syncing was
>> eliminated. This was with good de-coupling and hefty gauge star 
>> wiring etc.
>> No shared ICs or even on the same board.
>>
>> Bruce
>
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