No sound?

I’m going to start off by saying that I have absolutely no idea what I’m doing. I’ve built a few electronic kits, and circuit bent a few things, and that’s about the extent of my digital music and electronic experience. Someone gave me a Shruthi for Christmas. I figured I’d put it together. :slight_smile:

I believe I assembled the controller board without issue. The it boots correctly, the LEDs light up and change when I press the buttons and turn the knobs as described in the instructions. The LCD display also appears to display the menu properly.

The SMR-4 filter board has voltage in all the correct locations as described in the power supply check.

I am unable to tune the SMR-4 as described in step 14 because I don’t have a midi keyboard (or anything else midi). Is tuning required to hear sound? If so, I can go purchase one.

Without tuning, I have plugged headphones into the audio out but I do not hear any sound. I have tried playing the test note as described in the manual by holding down S1 for greater than 1 second, but I still do not hear sound.

You don’t need tuning to hear sound.

Try to probe the circuit with an audio jack (tip to point to probe, ring to ground) to find where the signal chain is broken:

You’d rather get a MIDI keyboard. How were you expecting to play a MIDI module without a MIDI source?

Thanks for the fast reply.

At point 1, I hear what I might describe as a “warm” buzzing sound that seems to fade slightly over time. At point 2, I hear a similar sound, but quieter. At point 3 I hear nothing.

  • Check that IC7 is correctly inserted
  • Check for bad solder points among all parts in the bottom left corner of the PCB ; and around IC8.

IC7 is inserted correctly. I don’t see any bad solder joints, but I could be wrong.

This is a picture of the bottom left. It may or may not be helpful.

I hear sound on the right hand side of the 10k resistor to the right of C13. I do not hear any sound on the right hand side of the 1.0k resistor directly below it. I have checked continuity across my soldering joints. That’s really the only thing I know how to do. Is there a more methodical manner for finding my mistake?

I am curious, is the sound I’m hearing at point 1, and 2 correct? I have to turn my speakers up all the way, and it’s still relatively quiet.

If you have a way of recording the sound at point 1 and 2, please post it.

The methodical way of troubleshooting a circuit processing audio signals is with a scope. Do you have access to one?

Otherwise: try removing IC7, connect a 10k resistor between pin 1 and -5V ; and measure the voltage at pin 1 when you change cutoff. Which values do you read at cutoff = 0 and cutoff = 127?

The sound from the first point starts at 0:03, and the second point starts at 0:19. The second point is very quiet and difficult to hear on the recording.

I do not currently have access to a scope, although I was considering purchasing this:
Would that work?

I removed IC7, and connected a 10k resistor between pin 1, and pin 11. I attached the com lead on my multimeter to ground, and touched the other lead to pin 1.
At cutoff = 127, I read -2.021.
At cufoff = 0, I read -2.059.

I believe pin 11 should have -5v according to this:

I’ve ordered the scope I mentioned above. I’ll report back when it arrives.

Please play a MIDI note while doing the recording ; and zoom out!

Well, I feel kind of silly. I plugged a midi keyboard in, and I had a signal at all of the points in the diagram. Then I plugged my headphones in and everything worked just fine. I’m a little puzzled why the test note didn’t do the job, but it seems to work fine now.

Thanks for all the help!

Hi! Excuse me, but me too, i have a similar problem. I probably made ​​a mistake when i built the SM-4 filter board. Because i have no sound.
The signal is broken at pin1. No problems with the other pin points, just pin1.

Are you sure the Shruthi receives MIDI?

I think, but I’m not sure… It is there a way to see if Shruthi detects midi? Maybe a led that blinks when shruthi synth receives a midi message? Anyway I connected the midi normally, the sequencer (ableton or a beat machine) midi out -> midi in Shruthi. Maybe it’s a manipulation with it, that I did’nt understand.

You’ll see a musical ‘note’ flicker on and off on the left side of most pages of the LCD screen when it receives midi data (Or right side of the screen when browsing patches)

Thank you very much, but it’s annoying because this musical ‘note’ flicker doesn’t appear on my display.

I tried to replace the shruthi with another synthesizer and it work. So the problem is not a bad connection with the midi cables. Either the external sequencer

Maybe I made a mistake somewhere during the assembly of Shruthi, or when either I have a defective electronic spare part, or so I don’t understand how to operate it.

Ok, so no flickering note, then its getting no midi data (Check midi channels too of course, although default, is 1).
However, there is only about 4 components between the midi in socket, and the MCU itself, so you won’t have much to check! Have a look at the 6N137 IC and its surrounding components. Particularly the diode for correct orientation.

NonOfficial MIDI In Troubleshooting CheckList

  • First First First Check if you haven’t scrambled up MIDI IN and MIDI OUT (things dnigirn!)
  • First First check if the MIDI Channels of the Sending Device and Shruthis match (in doubt set everything you find to OMNI, the Shruthis MIDI Channel to the non existing 0 which means OmniMode)
  • First, check the orientation of the 6N137 (Notch towards MIDI Connectors)
  • Probe pin 8 if its +5V
  • if you got a Scope Probe Pin 2 (Input Side), you should see 5V with 0V Spikes when MIDI Data comes in, if not resolder the MIDI-Connector 6N137 Pads
  • Probe Pin 6 Which is the OutPut for the same, if heres nothing replace the Optocoupler

Thanks. I think the problem comes from the optocoupler, because never voltage passes through any pin.

I’ll add to fcd72’s troubleshooting checklist: make sure that you have MIDI input going to the MIDI input jack, and not the output jack

@diplo303: you mean there is not even +5V on pin 8 of the opto?