SSL 1230 - Fader VC ADSR - Low output

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sonicwarrior
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SSL 1230 - Fader VC ADSR - Low output

Post by sonicwarrior » Mon Jan 09, 2017 5:02 pm

I have two Rev 1.2 VC ADSRs and both only output +4 V on normal mode and +2.5 - 2.7 on the two LFO modes.
The website says it should output +5 V.

They have four trimmers on board:
Can I adjust the output with any of those?
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sonicwarrior
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Re: SSL 1230 - Fader VC ADSR - Low output

Post by sonicwarrior » Fri Jan 27, 2017 3:58 am

Got an answer from Doug:
Again sorry for the delay. I wanted to be sure of the problem and I was correct. The LED is drawing down the output, and since the LED is also (indirectly) tied to the output of the module, the output will also be low.

The LED has a 220 ohm resistor that makes it pretty bright. I tried a 2.2K (2K2) resistor and the LED brightness was reduced but still (IMHO) acceptable. The module output can now go to about 4.7v. Only by removing the LED from the circuit can the output go to a full 5v in the present design. There’s no simple fix for this, unfortunately. Both me and Tom (the original designer) failed to catch this, and you are the first to notice.

I’ll update the specs on the web page to reflect this, but I’m afraid that there’s nothing that I can do with the circuit the way it is. I’d be happy to replace or remove the LED resistor for you but it’s the best solution I can offer at the moment.
4,7 V sounds acceptable to me so I'll try to replace the resistors myself.
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Post by dslocum » Sat Jan 28, 2017 4:07 pm

FYI - You can get about 4.7v if you reduce the brightness of the LED - still reasonably bright, IMHO. Just replace the existing 220 ohm resistor with a 2K2 (2200 ohm) 0805 size resistor.

The resistor on the 1230 VC ADSR is "R20". It's right next to the metal crystal near the CPU.

This will also affect the 1235 Envelope / VCA. The resistor number is "R220" which is near "U4".

I'll be sure this doesn't happen on future products. Sorry folks!
Doug Slocum
Synthetic Sound Labs
www.steamsynth.com
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