My resonance is nothing like in the YouTube videos? :(

Some background:
Got my first Shruthi-1 assembled, however there were few mistakes made during the assembly of SMR-4. First time power was plugged in, nothing happen, turned out the 9VDC wall wart had wrong polarity (I assumed it had standard polarity because I had never seen one that was not). Well anyways the protection diode did it’s job.

After swapping the polarity, still nothing happened, after careful inspection of each component it turned out I had mixed up 7805 and 7905, they were swapped. So I changed them the way they were meant to be, and now Shruthi powered up and everything seemed to be working.

Now going thru the presets just trying out the pre-assigned parameters, I noticed that when tweaking Resonance, it barely does anything, I just assumed I need to do the trimming. However when I started to trim stuff I quickly noticed none of the Loww, V/Oct and Reso potentiometers do anything to the sound (DC potentiometer worked). Now I wonder if there might be some hardware problem with my SMR-4 board? Resistor and cap values have been triple checked.

Also I noticed in the schematics there are these “Pimp my resonance” resistors that have unpopulated pads in the PCB, what is all that about? Do I just need to do some hacks to get the resonance to work?

No, you don’t need to do any hack to get the resonance to work.

Are you sure the V/Oct and Lowww trimmers do nothing? You should hear a modification of the cutoff value when they are adjusted.

Is the change in sound when tweaking the resonance pot subtle, or just non-existant? If it is subtle: turn the “Reso” trimmer even more. If nothing happens: check for a bad solder joint near the resonance trimpot or in all the parts around IC4 / IC5. A simple way to check that the resonance is working is by probing pin 7 of IC4 - you should hear the filter output’s signal with increasing level when you turn resonance up.


when i assembled my first shruthi i had the same problem…the solution was in trimming! At first i try to tirm, but nothing seems to happen. So i wait for some time, i didn’t like the way in which cut off and resonance sounds, so one day i try again to tune the instrument…i start to turn and turn my screw and after a lot of turning i started to heard that something was changing in the sound! Simply, before, i was not turning enough; try! maybe is the same for you!