Audio output feedback to audio input

Hey guys, first off just point me in the right direction if someone has already asked this. I haven’t managed to find a post…

Is it possible to feed the Shruthi output back into the input in order to get squirrely feedback without destroying components? I’m guessing that the simple way to try this is to put a STDP in line with a large value pot between the pins on the audio output and audio input jacks? I’m really tempted to try but I don’t want to fry anything…

You are not going to fry anything, but the last time I tried, the result sounded disappointing to me (if it had been more interesting, I would have added mod points in the circuit for that). Post your audio samples, though, I am curious about what kind of interesting sounds you might find…

It’s been done with the SID chip on the MB-6582 project and it sounds pretty good. But it works best with band pass filter though. So with those Shruthi-1 boards with low pass only may not really sound that great with feedback.

sounds like a fun task for our dear polivoks

Thanks doods. Will report back if I dig up any sweet tone…

Interested too in how that sounds!

i will try that, too.

One theorethical question: while normal Feedback shouldnt harm anything, what about amplyfied Feedback? (Through the send of a mixer with cranked up preamp for example) whould that break something in the shruthi?

The inputs have a 10k impedance so little current is flowing through the input resistors, even if your amp is cranking relatively high voltages. Over-voltage is not an issue here (the op-amp “sees” your amp through a 10k resistor, it’s not as if your external amp directly attacked the op-amp inputs). I am willing to send you a free TL074 replacement if you manage to damage the Shruthi audio input this way :smiley:

I cranked it through a board’s aux send loop back to input this weekend. Weird effects for sure (SMR-4). The strangest of which was seemingly random note jumping/pitch shifting. I think that this could be interesting for creating grungy, fidgety rhythmic textures a la Autechre etc.
@6581punk I took your recommendation and stripped the lows out of the loop and it does “free up” the sound. Without that highpassing, it just kinda craps out. I think that it’s worth designing the foldback into the new case I’m working on and my thought was to put a simple highpass filter after an engage switch and send level pot.
Now… simple RC highpass? Better ideas? All suggestions welcomed by this here newb :wink:

Hi sootsprite!

Why not reverse engineer the pole-mixing of Olivier’s wonderful Mission filter? :wink:

Mind you, I’ve already got very good variation from my SMR-4 MkII filter by adding the 2/4-pole and BP1/LP/BP3 switches - by adding those two switches and a single resistor you get six different filter responses that should work very well with your feedback experiments :slight_smile:


I missed something, what are the BP1/LP/BP3 switches?


I think he means DualSVF board not SMR-4.

The BP1/LP/BP3 switches are part of the new design of the SMR-4 mkII board. As far as I remember they are not present on the “old” version.

Check the mods and hacks section of the SMR4 mkII build instructions.

Cool, thanks!


Yep - Olivier’s pointed to exactly the correct place in his SMR-4 MKII build instructions, and these quick and easy mods make a huge amount of difference to the sound :slight_smile:


I missed those since it is a while since I built the board. I suppose adding software controlled switching would be possible?

@6581punk: you could add a 595 and a 4053 ; and without touching the code, piggyback on an existing filter setup, eg the 4pm one (even though those do a few software adjustments to the cutoff / resonance response curves in some circumstances).

Is this mod do-able on the SMR-4 mkI?

Yes, but there are no “user friendly” pads and labels to make it straightforward. You need to solder wires / resistors straight on the board.