Shruthi-1 assembly done, need help with tuning

Finally the Shruthi-1 is alive. Everything is ok except for the led number 5: while I was soldering I unfortunately cut the copper lane between led 5 and the resistor before it, so the led won’t lit anymore :frowning:

Find some pics here: http://muldee.blogspot.com/2010/10/shruthi-1-il-piccolo-synth-vede-la-luce.html

Now I need help for the tuning fase. I’ve tried to follow the instructions but there’s something I don’t get.
For the resonance settings I’ve set the oscillators at “none” and the envelope sa “50 63 0 0”. Now, with a E4 note played by my pc sequencer, I turn the reso trimmer all the way counterclockwise (till I hear the click) but I still hear sound… no way to mute it. If I turn the trimmer all the way clockwise the sound pitch to a very high level but is still there. If I put the ADSR to “0 0 0 0” the sound disappear (but I think it’s almost normal).
Someone can help me with this? Thanx.

Sorry, I’m not sure I understand what’s the problem here. Is there a position of reso such that you can hear a sound with all the oscillators off? You should be able to adjust its pitch with Lowww ; and adjust V/Oct so that it tracks the intervals played on the keyboards.

There might be some slight bleeding of the resonance sine wave through the VCA even when no note is played - if that’s what you observe. But this should be very low, less than -70dB.

Try to make myself clearer. While the oscillators are off I hear sound with EVERY position of the reso trimmer, so I cannot mute it in any way.

At point 3 of reso tuning I read: “Turn the Reso trimmer counterclockwise until you can’t hear any sound.” I cannot achieve it because my sound never disappear.

Hope I was clear now, sorry but I’m in a bit of confusion.

Does the sound disappear when you set resonance to a lower value? If this is the case, at which value of the “Reso” parameter the sound starts disappearing? Does the pitch of this sound varies with the value of the cutoff?

Have you checked that you haven’t swapped 2 trimmers, and that all the resistors around IC9, IC5 and IC4 have correct values?

Ok, I’ve checked the whole board and everything is in its own place, no swapped trimmers, no wrong resistors, nothing wrong.

Let’s do it step by step:

  • as the shruthi goes on I click on button 1 till the led 1 is lit; I’m in the Osc1 screen;
  • I rotate the first knob untill the Osc1 is set to “none”;
  • I click again on the button 1 to lit the led 2; I’m in the Osc 2 screen;
  • again I use the first knob to set to “none” the Osc2;
  • then I click on button 2 to enter the filter screen;
  • I use the four knobs to set the four parameters to “50 63 0 0”

At this point, according to what is written on Reso Tuning at point 2 and 3 I should play an E4 note and hear a sound; then if I turn counterclockwise the screw of the R23 “reso” trimmer I should be able, at some point, to put in mute the sound.

Is it correct or I’m doing something wrong?

Thank you for your patience.

What you are doing is correct.

Your problem seems to be that no matter what is the position of the trimmer, you hear a sound. My question is: can you kill this sound by moving reso down (eg: 50 50 0 0 on the filter page)? Does the pitch of this sound change with cutoff (40 63 0 0) or (60 63 0 0)?

Maybe there’s a short near the trimmer which explains why you always get full resonance no matter what is the setting of the trimpot. But first I need to make sure that the sound you hear is the resonance - that’s why I’m asking you to tweak the cutoff and resonance setting to see how it changes.

Back home I turn on my shruthi, i re-do the steps I wrote in my previous post and… guess what? No sound.

Then i turn the screw of R23 clockwise while playng E4 and, in a wile… sound! Further turning cause a slight increase of the pitch and the sound gets louder and distort (as it supposed to be).

If then I use knob1 to modify cutoff it changes the pitch while resonance values less than 63 cause the sound to disappear.

I suppose this is normal, isn’t it?

Yes, this is normal. Tune R23 so it stays in the zone between “no sound” and “distorted” and you’re all good!

Tank you man, for your patience and for your extremely quick answers.

i also have some troubles tuning my shruthi :confused: i got exactly the same problem as muldee had, the sound wont disapear or even change when i turn the reso trimmer. the strange thing is, that it worked as it should, when i tryed it the first time, after i finished the soldering. didnt have time to finish it, so yesterday i wanted to tune it again but it doesnt work now as it allrdy did…