Shruti-1 Filter Board -1 : no self-oscillating but strange sound


I used the Shruti-1 for some time and it works perfectly but I wanted to redo the “The tuning procedure” :
(Osc1 :none, Osc2 : none, Fil cutoff: 64,Fil reso: 63,Fil env and LFO mod: 0)

I realized that I had not sine wave but this strange sound :

1st track : i play C1 C2 C3 C4 on keyboard
2st track i play the SAME note ( but I hear more notes
And 3st track stange thing : I raise it above my desk, I tipped, and then I put it on the desktop )! :0)

I would not disassemble it now because it works very well but I would like to know what you think
It’s here :

Thanks !

Just had a thought - you could have different adhesive front panel films to add colour/special logos for the different filter variants, but keep the same black case with rear panel legends for all models.


I’m completely down for the metal case, flat black like my heart.

Im in for a Metal case, too. I’m the greedy collector :wink:

As much as I like Franks Plexi cases, I would definitely be interested in one or two sturdy metal cases for the road. They should have a protective window for the LCD though.


  1. I think 50 Euros is a reasonable price for a metal case with all holes completed, spacers in place, and finished artwork, compared with the 25 Euros for the current bog standard clear acrylic case - after all, this should also open up the Shruthi-1 to more gigging musicians in a more hostile environment.

2. I suspect though that this would have to be a one-off design as far as artwork goes - offering differently coloured versions with different logos to house 4-pole, polivoks et al would mean a higher price from the case manufacturers, although you could possibly offer the aluminium cases finished or uncoloured for personal customisation.

3. However, even then you could possibly do a one-off new coloured 100-case run for each major new filter design as it comes out.

4. If you contemplate researching this option further you could always make sure the case height is around 5.25-inches so that three Shruthi-1 metal enclosures could be bolted side by side into a 3u rack shelf :slight_smile:


Note that the noise in the track 3 is ONLY during the tuning procedure and especially when playing note on keyboard :

  • away from the internet box : no problemes
  • Near the internet box : a lot of strange backgrounds sounds !

When playing Shruti in “normal” mode : no problemes near the internet box …

@yewtreemagic : Nice link !

To give you an idea, using the same manufacturer as for the MIDIpal (very serious people but very formal and slow), there would be an initial cost of 500-600€ for them to go over my not so formal drawings, redo them with proper CAD tools, convert the model into CNC machine programs ; and then taking taxes into account I could sell the boxes in the 40 - 50€ range with very little margin. At this price we get the all custom deal - any kind of milling/drilling, spacers crimping on the bottom of the case, silkscreening. All in all, it’s roughly the same price as starting with a Hammond case and having it drilled/milled/silkscreened to my whim. Prototypes would be ~100€ a piece. It might be possible to get it done cheaper elsewhere, but I found that establishing a relationship with old-school firms doing this type of work takes a lot of time, phone calls, and is not always pleasant. So it needs to be a run of at the very least 100 pieces to make it worthwhile and not too expensive for you.

@Lucchio: I’ve also noticed some background hum on my Shruthi-1 output when I place it near my effect rack, but it’s very quiet when given a little space to itself :wink:

Your track 3 breakthrough and my hum would both disappear if enough people expressed an interest in a more expensive metal case for the Shruthi-1, which would also make it more suitable for live gigging.

We’d lose the gorgeous plexi colours, although I suspect some artists would offer custom paint finishes for a metal Shruthi-1, as they do for products like these:

The Art Of The Stompbox

Some stompbox artists and their designs are featured here

Sorry for the derailment :wink:


Everything works ok !
But I think I prefer self-oscillation set to a minimum
Shruti sound very aggressive if this setting is too high
For The strange sound of track 3 : " I raise Shruti above my desk, tipped it etc …" : Shruti don’t like "internet box and wifi "
Thank you

… I think that i must resume the procedure at the beginning and read the “Step 14: Tuning”
I will disassemble Shruti and I give you some news thank you !

Have you tuned the resonance trimmer first? It should be tuned so that the filter reaches self-oscillation.

Its a SMR4 mk1 board filter
Sorry for working from “init” patch i read it but I forgot … I have “user” patch i suppose it’s the same thing
There is the result when playing C1 C2 C3 C4 on keyboard, it does not look like a nice “sine wave” ?
(I don’t know how embedding links in Vanilla sorry)

Hello my English is so bad ? :0)
Or my explanations are not easy to understand ? :0)

I will give you the link to sound files :

Did you start from the Init patch?

Which filter board is it? You need to work from the “init” patch to do the tuning procedure. Looks like you used a patch with random cutoff modulation for your audio samples.

Any followup on this? I’d kill for a metal case.

Metal case, did anybody mention metal case ??? I’ve been looking for industrial standard cases, but all in all i almost come to 100 bucks…just a bit too expensive for an ugly case of Shruthi size.