Soundlab Ultimate/Expander build question.

[MartianModular]

Hello all,

I'm on a couple of other synth DIY forums, so if you've already seen this inquiry, please excuse the cross-post.

I'm in the process of troubleshooting my recent MFOS Soundlab Ultimate and Expander build. I've worked through a number of issues, and the synth is functioning well, with a couple of notable exceptions.

Currently, I'm tackling a misbehaving VCO1. It exhibits a slightly shaky characteristic on sustained notes. I would describe it as "jittery". Scaling and overall pitch stability is excellent.

The other two oscillators also have this slight random jitter, but it's subtle. Totally usable.

On VCO1, this jitter can be heard from all outputs, and directly off the output pin of U2.

I've replaced U1, U2, the 100k coarse tuning pot, C7, Q1, upgraded and replaced C4 and C10 decoupling caps with 2.2uf bipolar electrolytics, and replaced the 3904's with a new matched pair.

Any suggestions from other Soundlab builders?

Thanks!

[Grumble]

If you'd add a schematic or at least a link to that, would increase the relevant answers dramatically...

Just sayin'

Other that that: to this forum

[MartianModular]

Thanks! Here's a link to Ray's circuit description and schematic. If you click on the description for VCO1, a schematic is included.

http://musicfromouterspace.com/forums.html?CATPARTNO=&PROJARG=SOUNDLAB_ULTIMATE%2Fpage2.html&MAINTAB=SYNTHDIY&SONGID=NONE&PLAYONLOAD=FALSE&VPW=&VPH=&CATMOBISTATUS=&SYNTHDIYSTATUS=CONTENT&SEARCHTERM=

[MartianModular]

Just in case the link doesn't cooperate, here's the schematic.

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Description:	VCO1
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[MartianModular]

I moved the Soundlab into the studio and recorded three tracks. All direct out from the individual oscillators. There is a bit of jitter on oscillators 2 and 3, but VCO1 is the worst, by far. Three links to follow.

https://drive.google.com/file/d/11WJbWks0HotsIrDLlCZlgljTxGUzXtVF/view?usp=drivesdk


https://drive.google.com/file/d/1JDj4-et9mHmKLc4_LJthpNPMkskydiC3/view?usp=drivesdk

https://drive.google.com/file/d/1yBXiuvCesThN81y0JMxrEPtYj-PiD_ko/view?usp=drivesdk