[sdiy] what opamp for "warmth"? (I know, I know...)

René Schmitz synth at schmitzbits.de
Sat Apr 8 14:35:38 CEST 2023


On 07.04.2023 15:39, Roman Sowa wrote:
> The transistor is controlled purely with base current, so I'd say they 
> were selected for beta to provide similar amplitudes after VCAs 
> between voicces.
> In my experiments I played with base resistor to achieve needed gain 
> at fully open VCA


That makes sense. In the MS20 they also changed (cut) resistor values 
depending on the colour code of the transistor.

For a mono synth, a bit of variation could be tolerated. (Because you 
can level-match them externally if you ever use two at a time at all.)

But in a poly you'd notice variations on individual voices quickly.


Best,

  René


>
> Roman
>
> W dniu 2023-04-07 o 13:51, René Schmitz pisze:
>>
>> According to the schematics the transistors shall be selected. jx3p 
>> also says "SEL".
>>
>> Anyone would know what for? Equal gain?
>>
>>
>> Best,
>>   René
>>
>> On 07.04.2023 11:04, Adam (synthDIY) wrote:
>>>
>>> David G Dixon via Synth-diy pisze:
>>>>>>> Whatever the VCA is in the Korg MS-20 really warms up the sound 
>>>>>>> of that synthesizer.  You can find the schematic on the 
>>>>>>> internet.  I have something redrawn by a fellow named Marjan 
>>>>>>> Urekar that I looked at years ago.  It involves two transistors. 
>>>>>>>  It is evidently also the VCA used in the Roland JX-3P.
>>>
>>>
>>> Interesting.... here's the JX3P version
>>>
>>> grab 2023-04-07 at 6.57.54 pm.png
>>
>>
>>
>>
>>
>>>
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>>
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