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

René Schmitz synth at schmitzbits.de
Sat Apr 8 14:27:00 CEST 2023


On 07.04.2023 23:06, Tom Wiltshire wrote:
> For synth pads, the envelope would be much slower, so the control feedthrough wouldn't be so obvious. I'm not saying it wouldn't *exist* but a slow rise of 100msecs+ in DC level is a lot easier to get away with than a sharp hit!

Indeed.

If you look at the JX3P schematic you can see that the control voltage 
is filtered, with 2* 100k / 22n. This reduces the speed of the 
envelopes. Similarly done in the 909.

> Tom
>
>> On 7 Apr 2023, at 19:24, brianw <brianw at audiobanshee.com> wrote:
>>
>> Speaking of control feedthrough, there was a paper written about modeling the TR-808 where it was mentioned that the "pop" or "click" from the CV was beneficial for percussive sounds. That wouldn't be so good for synth pads!
>>
>> Brian
>>
>>
>> On Apr 7, 2023, at 4:51 AM, René Schmitz <synth at schmitzbits.de> wrote:
>>> You'll find the same VCA in the 909 in a few places. (Bassdrum , Toms, Clap..)
>>>
>>> Note how far the signal is divided down.
>>>
>>> It's noisy, and nonlinear, and has some control feedthrough. Show what you can get away with for a single monophonic signal.
>>>
>>> The MS10 had the single transistor, the early "Korg35" MS20 had the same.
>>> The later MS20 had a second transistor, which makes things more linear/symmetrical and you can run larger amplitudes -> less noise.
>>>
>>> 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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