No sound with SMR-4, only noise past point 6 on Shruthi 1 chain

Hi everybody !

I just finished my Shruthi 1 with SMR 4 filter, display works fine but unfortunately the sound doesn’t (I don’t have a MIDI keyboard yet so I used the test note).

I tested the 8 points mentioned on this shruthi chain with jack cable and headphones, point 1 to 5 give a raw then filtered sound, but past 6th nothing but noise ! I tried to swap the TL074Ps, but same problem. So I thought it to be a soldering problem and I fixed some around IC8, but still nothing.

Can you help me fix this problem ?
Thanks !

Well, I wouldn’t say the problem is solved. You’re only enjoying half of the filter ; and if the poles 3 and 4 are not working, the resonance should not work either.

Well, problem solved ! I switched the poles jumper on “2” instead of “4”, and now I have a nice sound :slight_smile: !
I guess there is a bad solder on the circuit related to pos “4”, I may try to fix it and try again on “4” a day.
Anyway thanks for helping, I’m really happy to finally have fun with this awesome synth !

Yes, because I didn’t have anything else available (I’m a boarder in a school), but I noticed how loud the sound was… However, now that I know, I’ll be careful, thanks ^^ .

Check that the poles jumper is in place. Check every solder point around IC9.

you probed with headphones only? you need to do it with a high impedance audio input.

Before I do anything wrong, I have a question about the 4 unused holes mentioned in the building tutorial (old one) :

"Pause: Ain’t I missing something?

You might have noticed 4 locations where one could solder a part with a 2.54mm pitch — below IC4, and near the Resonance trimpot. These pads can be used to solder parts (Zeners, diodes, LEDs…) to tame/shape the sine wave the filter will emit when it self-oscillates."

If I don’t plan to use any component here, do I have to solder a contact wire between these holes ? Maybe a stupid question, but this might be why the resonance doesn’t work ^^ …

No, you don’t have to solder anything here, see the photo of the assembled board.

no. you don`t have to solder anything there.

(edit: cross post - pichenettes was way faster)

Yeehoo !

I just resoldered some points around IC9, like pichenettes advised, and it worked !
The resonance works fine for now, I didn’t notice any other sound problem.

Thank you for your help !