Shruthi XT control board voltage drop

I have a Shruthi XT control board with the Dual SVF filter board. When I power up and test the voltage of the filter board I get a solid 4.98 volts. When I connect the XT control board the voltage drops to 3.98 volts. I’ve searched for shorts and incorrect components and have yet to find anything wrong.

I can select the Dual SVF filter from the filter menu but if I turn the unit off, it doesn’t remember the filter settings.

I don’t know if this is related, my display flickers and displays random values. I’ve read quite a few other people having this same issue but I’ve yet to find a resolution to this problem in my Shruthi from other peoples similarly described problem

Any suggestions would be greatly appreciated


The voltage drop could be caused by your power supply delivering not enough current. The problem could be made worse if you used a LCD display whose backlight draws a lot of current.

The display flickering/random values is a direct consequence of a power supply instability.

The Shruthi only remembers the settings if you save them. When you are on the settings page, press the load/save button, and turn the encoder to confirm.

I’m using a New Haven display product - NHD-0216K1Z-NSR-FBW-L. I’m pretty sure my power supply is 500 mA, 9v I’ll have to look later on to confirm. I thought i had saved my settings, but I guess not. Will have to confirm that as well. This won’t happen till next Tuesday though as that’s my dedicated synth building day.


Ok, power supply is 1000 mA 9v ac. Could the flickering display also be a faulty 74hc165 reading weird data or a 74hc595 outputting weird data?

You need an AC/DC power supply, not AC/AC.

Thanks @eelco …don’t know how I messed up that important detail.

Power supply is sorted, I’m not getting random values on the screen, voltage is a solid 4.98v. I just have to wire the analog volume pot and put it together. Oh yeah, gotta solder the ghost eyes on the dual svf board too. :slight_smile:

Ok, hopefully this is the final issue. I’ve wired my Shruthi XT for analog control. I flew in the face of the recommended digital control and installed 688-RK09D113F25C0A from mouser. However I’m not getting anything from the output. Jumpers are installed as instructed. I’ve the schematics but don’t know where to start looking. If someone can point me in the right direction, that would be appreciated.


Is MIDI working (do you see the little note symbol appear (briefly) when you play the keyboard? Check the MIDI settings if no note appears.

Otherwise use the ‘jam’ button to play something without the keyboard.

Reading the thread above, setting the correct filter and saving that settings is essential.

Ah, and make sure the Shruthi is in XT mode :slight_smile:

@eelco Thanks for the response. :slight_smile: I’m getting midi, I can see the midi note symbol when I play on the keyboard. The filter setting is correct and now saved. I’m gonna have to double check and see if it saved the XT setting. …because now that I think about it, I don’t recall saving that setting. :thinking:

It’s not a setting that you can change once the Shruthi has booted, but one that changes while you boot if you press the right button :slight_smile: (see manual!)

The splash screen just after booting tells you which version of the Shruthi hardware you’re using (there are three). There is a setting to turn the splash screen on or off (might be worth switching it on).

…yeah, I know I have to press the encoder when powering up the machine to select the version, and keep doing it till the right one is selected. I’ll dig into the manual for the splash screen settings.


Ok, I have signal, I can hear the oscillator when the sequencer is running from the osc pin and the legs of various chips on the board and i can hear the both filters working. I still don’t have output to the 1/4" jack though. Here’s a part of the schematic where I lose signal though.Lost signal I lose signal after the 100K resistor (R14) Maybe that capacitor is bad (C9)? Maybe I ruined it because I used an AC supply when I first powered on?

Help! :thinking:
Lost signal

I’ve found either a dead/broken trace going from R3 to the bottom pin of R2. I kludged the connection as reflowing didn’t seem to work. I can’t see a trace on the board either so I’m not sure it’s even there. I now have audio out but it seems very quiet. …but it’s progress. :slight_smile:

What would cause a low level at the output?