Shruthi-1 SMR4 no audio

So I ran the troubleshooting test in the SMR4 MkII manual and all test points produce no sound whatsoever. To verify I’m performing the test correctly I have the controller board disconnected, power going to the filter board, an external synthesizer connected to the input of the SMR4 filter board playing sine waves. And probing the circuit with a TS cable with two jumpers one going to ground and the other being used as a probe. Any advice? I can post pictures if necessary.

You have to do the test with the control board connected (with jumper wires).

No audio will flow through if there is no VCF or VCA control signals sent to the filter board.


Most problems are the ±5 voltage on the filter board. Please test this before!
IC2 Pin 8 = +5 Volt
IC2 Pin 4 = - 5 Volt

Best Rolf

Volts on IC2 are 5.01 and -4.9. I tried running the test again with the boards connected through a bread board still no audio.

Did you miss the jumper wires on the audio in/output jacks?

A photo of your assembled board would help!

Jumpers are soldered in well, will post photos when I get home.

Hi Olivier and co,

Totally sorry to be pulling past skeletons out of the closet like this but I finally want to get around to finishing my Shruthi. Here are the pictures of where I left off nearly two years later.

Please forgive me!

You might want to reflow the IC socket pins (adding more tin): not much solder there (do take out the ICs first!).

Also, the pots and push button pins almost seem not to be soldered at all - please use some more there too.

BTW: when you switch it on, do two of the LEDs light up?

I did not solder the pots/buttons all the way in yet for reasons I don’t recall, however when I switched it on the two leds do indeed light up.I would actually like to retest the noise issues with some midi cables and a sequencer but I won’t be able to pick those up till tomorrow.

I have the unit working accordingly now, however it seems I have lost the screws/spacers needed to finally assemble the enclosure. Can anyone refer to a source where I can get the necessary hardware?

Depends where you are - I found ebay to be a good source for stuff like that.

These guys have lots of spacers (and IC sockets etc.):

For screws+nuts: your local hardware store (they are pretty standard).

I have some stock if you need a few urgently.