[sdiy] Coarse and Fine Pots

[Michael E Caloroso]

Those Oberheim SEM tuning pots are called concentric ball bearing reduction
pots, long out of production.  Tom Oberheim admitted that he never liked
them.

MC

On Sat, May 24, 2025 at 9:34 PM Michael E Caloroso <
mec.forumreader at gmail.com> wrote:

> Just sum the CVs from both pots to the CV summer opamp, configure the fine
> tune pot to lower gain.
>
> MC
>
> On Sat, May 24, 2025 at 3:59 PM Terry Bowman via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
>> I'm upgrading my existing Oscilloscope Artist:
>>
>> https://www.astarcloseup.com/2016/02/the-oscilloscope-artist.html
>>
>> I really need to add a fine tuning pot to two of the oscillators. I love
>> the planetary mechanisms used for the VCO tuning on the Oberheim SEM but
>> unfortunately they appear to be unobtainium right now. Are there any dual
>> concentric pots with different resistances? It seems to me that a ratio of
>> about 5:1 would be close to ideal so that would be 100kΩ/20kΩ.
>>
>> If not, can I just put a resistor in parallel with the fine pot? I know
>> that the latter changes the curve and linear is preferable.
>>
>> A related question: how does the sync to oscillator C work?
>>
>>
>> Terry Bowman, KA4HJH
>> "The Mac Doctor"
>>
>> https://www.astarcloseup.com
>>
>> #1: There is no substitute for good tools;
>>
>> #2: Always use the right tool for the job.
>>
>> Linn Westcott
>>
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>
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