Help with my assembly: SMR4 filter 4 poles resonance not playing

I tried following the instructions to tune the filterboard, but I can’t hear any self-oscillation, albeit the filter seems to work…

What is the voltage on the middle pin of the trimpot? Redo the 3 solder joints of the trimpot.

Sorry, I sorted that one, I was just being stupid, the filter issue is now the only problem.
And this synth sounds better than the demos, it’s lovely!

At the exception of self-oscillation, does the resonance control do something? Photo of your assembled board?

Resonannce seems to work as expected, I tried to put the oscillators to none, and only have noise on the mixer. With the cut off around 100 if I sweep the resonance I can hear the frequencies being increased, same as my other synths, but oddly enough I can’t hear the sine.

What’s that weird resistor? What is its value (looks like 22 ohm)?

I couln’t find another 220R so I replaced with a different one, it should still be 220, (black, black, red)

hmmm, no, that’s 22 ohms. You need brown red red


rather red red brown gold to be clear

Perfect! I have some resistors around and there’s a few red red brown gold!
I’ll do that tomorrow, too tired tonight…


Cool beans :slight_smile:

No victory candy for me yet…

Just so I understand, what difference can that resistor make?

It shifts one pole of the filter by a decade, so you don’t get the 180° phase shift that allows resonance, instead you only get a 135° phase shift.

You’ve built a 3-pole filter :slight_smile:

4 pole filters are so last year…

I had my Victory Candy!

Not a perfect build, but for my very first DIY experience I’m super happy.

I’m sure I’ll get a Polivoxs filterboard soon…