Soundlab Ultimate/Expander vco question.

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MartianModular
Learning to Wiggle
Posts: 5
Joined: Sun Jun 17, 2018 7:34 pm
Location: Canada

Soundlab Ultimate/Expander vco question.

Post by MartianModular » Mon Mar 02, 2020 5:13 pm

Hello all,

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 behaviour. I would describe it as "jittery". Scaling and overall pitch stability is excellent.

The other two oscillators also have this slight random jitter, but much more subtly. Totally useable.

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 opinions from other Soundlab builders?

Thanks!

johnstilton
Common Wiggler
Posts: 67
Joined: Tue Oct 09, 2018 10:31 am
Location: West Chicago

Re: Soundlab Ultimate/Expander vco question.

Post by johnstilton » Tue Mar 10, 2020 8:11 am

I should be done wiring up a front panel for an ultimate this spring. I cannot help you with your issue yet, but if I have a similar issue (or any other issues) I will post about them here in this forum for sure.

MartianModular
Learning to Wiggle
Posts: 5
Joined: Sun Jun 17, 2018 7:34 pm
Location: Canada

Re: Soundlab Ultimate/Expander vco question.

Post by MartianModular » Fri Mar 13, 2020 5:40 pm

Thanks. After further research, experimentation, and help from other Soundlab owners, the general consensus is that I need a higher quality power supply.

I've ordered a Frequency Central psu, and will report back after I've done the upgrade.

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