Filter sounds a bit distorted

Just assembled shruthi… Almost everything works fine, only the sound is a little bit distorted… When i completely remove 2pole/4pole jumper at all, output sound is ok, not distored (but when resonance is lower than 2-3 it is also really quiet), it is a bit silent (not much, but there is difference compared to loudness when filter mode jumper is connected) but it is not distored at all… When i connect jumper (no matter if it is in 2p or 4p mode) it is louder but also distorted… I tried lower reso trimpot but it doesn’t affect distortness of sound…

I measured each resistor during soldering, so there is small chance that some is incorrectly soldered, i checked all other stuff many times but can’t found any mistake on filter board …

Please, any idea what could be wrong ?? Or small distortion is normal behaviour of smr4 filter ?? Any advice welcome, thanks;)

I thought that filter board doesn’t work at all with the jumper removed?? (Maybe changed in later revisions. But I doubt it?). I’d have a scout around for shorts…

There shouldn’t be any sound when the pole jumper is removed, except maybe some very faint bleed through the PCB.

Which device is your Shruthi connected to? It looks to me that this device has a HUGE input gain - which would explain why the normal sound is distorted and why a faint bleed sounds as a “normal” level.

Do you have a scope to check the amplitude and shape of the output signal?

i connected it to alesis linelink usb sound card so huge input gain can’t be problem (it works fine with my DSI tetra or NordLead2) … i tried also connect directly to shruthi my headphones, but the result is always same - with jupmer connected (no matter in which position) - sound is distorted, with jumper disconnected, sound is OK only little bit quieter … it is almost silent inly when resonance knob is st to 0-2 … which resonsnace >3 it sounds normally …

sadly haven’t scope … but signal doesn’t look to have too big aplitude - i checked input gain montitoring at alesis linelink and amplitude looks approx same (or in same range) as the other HW synths which i have …

At which stage does the sound get distorted?

It is likely that the problem is a bad solder joint/short in the area around IC5

not sure that i understand what you mean with “which stage” :) if you mean JP3 stage, then it doesn’t matter if 2 or 4 set sound is always distotred … best it is heared when CUTOFF is almost closed (bass sounds) … and it is distored also when i set R23 (reso) trimpot the way that it is far away from self-oscillations …

anyway, thanks for tip, i will deeply check everything near IC5 … but, the trimpot R3 (DC offset) works good, i successfully set ideal DC offset, so for me looks IC5 works correctly …

one thing more … when i change between 2/4 modes JP3, the filter character is not too much different, only output sound is little bit (not much, just very little bit) more loud in 4 mode compared to 2 mode … generally there isn’t not diffrence between filter character which i expected and which is common between 2POLE and 4POLE lowpass filter mode … maybe it have something to do with this problem… filter simply sonds almost identically in 2 and 4 JP3 modes … and much louder and little bit distoreted (but again not heavy distored, just small ‘drive’) compared to when JP3 isn’t conencted at all …

here is sound example, i recorded 3 short samples, only one oscillator, saw, resonance set to 50 … first one is JP3 not connected at all, after this is JP3 in “2” mode and then JP3 in “4” mode
http://www.raysubject.sk/shruthi/filter_test.mp3

here is foto of my filter board …
http://www.raysubject.sk/shruthi/filter_board_top.jpg

“Which stage” means follow the audio through the numbered area’s provided on the diagram… Probe those area’s and listen… Somewhere between 1 & 8 the ugliness happens, giving you a clue where the fault lay on your board.

also the fact that you have sound without the pole jumper set indicates some sort of bridge somewhere.

Pichenettes: sorry, i’m dumb and blind :))) i didn’t saw the numbers at your screenshot :))) okay, so at stage 7 it is still OK ! Only at stage 8 is it distorted …

Okay i solved the problem :slight_smile: imserted trimpot into stage (7) connector and lowered signal there … Now everything is fine…

that’s where you usually connect the output volume pot, or just bridge the two pads for full volume.
do you still have sound without setting the pole switch jumper?

Little bit yes but it’s not issue for me :slight_smile: i simply set jumper to (4) mode, tweaked output with trimpot R2 so it is not distorted and now i’m really satisfied with sound :slight_smile:

It seem that I have a very similar problem,maybe exactly the same shame you don’t succeed to found the cause…

It seem that I have a very similar problem,maybe exactly the same shame you don’t succeed to found the cause…