No resonance


I finished assembly my Shruthi today and began the trimmer process before case assembly (stock Shruthi-1 kit with smr4 filter board). Anyway, everything powers on and looks good, synth sounds cool, pots, switches, led’s LCD, all work. Power section tested fine with multimeter.

So I started the trimming process and was getting incorrect behavior. I adjusted the synth setting to what is recommended in the assembly instructions, but I don’t get a sine wave with the oscillators off, just a little pop type of sound on midi key press, which varies slightly in timbre when I press different midi notes (it’s not pitched, its a short noise that does not sustain). The trimmers have little to no effect.

Anyway, I went back and started adjusted settings on the synth and noticed the resonance control has basically no effect on the sound. Cutoff works, envelope works, but resonance not only doesn’t self-oscillate, it pretty much does nothing at all.

I have the poles selector jumper in, set to connect the middle pin and the “4 pin”. Is there a certain component or solder joint that I should be looking at to explain this? Thanks.


you could always try to work over the resonance trimpot again, maybe you’re lucky and that’s it

Also, check the voltage at the left pin of the 33k resistor just above C6. It must go from 0 to 5V when you increase resonance.

Check that velocity and envelopes does not modulate the cutoff frequency of the filter… A fast envelope could possibly produce what you get and the velocity makes tuning the filter near impossible…

Figured it out. You wouldn’t believe what the problem was. I didn’t have the test jumper for resonance hooked up between the 2 boards. Doh! Thanks for your exceptionally fast responses.

PS this synth is pure insanity. I love it already!


Thats a new one…


I took a little break, and when I came back to troubleshoot I noticed it immediately. At least it wasn’t my soldering!

Just assembled the case, glad it’s finished, time to make some music…