Tuning issue with Resonance

Hi all,

Just finished the Shruthi SMR-4 board v.07 and Control board v.07.

I’m not coming passed the Resonance Tuning part.

I don’t have a scope to check the wave forms.

Here is a small WAV file of the sound that I am hearing http://www.cubikplanet.nl/download/shruthi.wav

What ever I do, turning R23 clock or counterclockwise… nothing but the sound in the WAV comes out of the speakers. Every pop you hear is the note getting played.

Any ideas guys?

Thanks for now!

Since you don’t have a scope, you’ll have to use the same trick as the other ones… Try to find where the signal path is broken by connecting the tip of a jack to various points on the boards.

Ok, did some probing with a wire…here are the results…

Probing on http://farm5.static.flickr.com/4126/5121443874_29beae646b_z.jpg> OSC on Control Board = OK —> Sound is produced
Probing on http://farm2.static.flickr.com/1058/5120841209_0b1784819d_z.jpg> IC3 TOP 1 = OK —> Sound is produced
Probing on http://farm5.static.flickr.com/4112/5120841437_564005e698_z.jpg> IC8 TOP 8 = NOT OK —> NO SOUND

So, conclusion ----> IC8 is screwed or different problem?

Thanks again!

Ok, did some more checking… switched IC3 and IC8 to rule out a broken IC8, but same problem… so will have to check further… any suggestions are welcome!

Check all resistors + caps around IC8, check means resolder every pad that looks not perfect. EVERY!. Thats a 85% chance the problem will then disappear (at least the problem around IC8) as 85% of all problems here are somehow bad solder joints.

OMG how stupid I was…after checking all the soldering…after re-doing some of the soldering and still couldn’t find it I saw it… I’ve placed one 2N3904 the wrong way on the board… stupid slams head on the table

Anyway… I’ve de-soldered the transistor and bought a new 2N3904 and just put it in… but I still have the same problem, no sound on IC8 while probing…

So, could I have broken something else now??

I’ve now double checked all components on the board and it’s the only (lucky) mistake I’ve made, but do you guys have an idea why my problems are still not solved?

Hides in shame hoping for a good answer/solution.

Could you post a pic of the front and the back, maybe we can spot something.

Ok, here are the pics:

FRONT: http://www.cubikplanet.nl/download/front.jpg
BACK: http://www.cubikplanet.nl/download/back.jpg

Difficult to get the back properly without making it look shiny or clean ish… the back looks on pic different then in real life… anyway lets see if you guys notice something strange…

Thanks for looking!

Front looks good, i spotet a few joints that look suspicious… its not easy seeing clear bit i would probably start resoldering the pink marked spots…

Ok will give that a go and let you know how it turned out!

Thanks so far!

Ok, after numerous tries to look what could possibly be wrong with my solder work (the pic doesn’t give a good representation) I’ve went to a friend with an oscilloscope and did some debugging… but still no luck… it all just didn’t make sense… something had to be broken… but I get the feeling it was the Resonance Trimmer in the end that might not do the job… but also that was guessing and didn’t want to bother replacing it anymore…

So, I’ve ordered a new analogue board the other week, got it in, ordered the missing components that I didn’t have in stock and started from scratch.

Finished the analogue board yesterday and now it works perfectly.


  • Really happy it works now
  • Little bit annoyed that I had to spend money on a new board
  • I guess it wasn’t my soldering but either a faulty board or a component that was not working…still I couldn’t find it… sigh… oh well

Thanks for the help and pointers people gave me though, much appreciated!


cool you have one running.
but are you really sure about the problem not being bad soldering at some point? if you read the troubleshooting threads you’ll find that almost every problem is related to soldering issues rather than a bad board.
maybe, if you have access to a scope you could now make a few measurements to compare the boards. i mean, if it turns out to be just a damaged component or bad soldering you already have the first half of your second Shruthi in hands!

Yeah rosch,
the trick to polyshrutism is to order an uneven amount of boards :wink:

haha yeah works always you can also increase the effect by ordering even more mcu’s!

yeah, the rule #1 to polyshruthiism: always order n+1 parts…

Hey guys, almost 100% positive that it’s not my soldering skills. I’ve done many synth projects in the past, have a good soldering station, pretty sure my soldering is ok. Anyway…you guys could be right of course, but never experienced issues after my soldering…

Anyway… it works now and that’s the main thing.

The old analogue board I will keep of course and will figure it out eventually…

Like the comments about the n+1 parts…you never know… might order my next Shruthi-1 later this year… first time to enjoy this one and make some music with it… :slight_smile:

Thanks again for your pointers and help!