A new Shruthi-1 filter board is coming

Ok let’s face it… Most of the Shruthi-1 filter boards are very clean and hi-fi sounding! It was high time to fix this, and I am glad to announce that I have finished the design of a filter board a bit more… aggressive.

It is based on the classic Polivoks circuit. It doesn’t require any rare chip besides 2 fancy but widely available op-amps (LM4250, <1€).

In addition to the BP/LP selection ; 2 additional settings have been introduced:

  • a VCA overdrive to add a big tanh fuzz on the output. LOUD!
  • a filter FM feedback setting, which feeds back the output of the filter to its cutoff control for plastic/rubbery sounds.

The filter covers the 10 Hz - 10 kHz range (a bit dark), but there’s a mod that can make it track 16 Hz - 16 kHz at the cost of more distortion (as if there wasn’t enough…)

I’m going to order the prototype board tomorrow evening, so if everything goes well, the boards should be on the store in early december, along with a firmware update to support the new menus for mode selection.


I want one!

Do you use the Output Expander or the digital Line to switch the Modes?

Is this the right part ?

Give it to me! NOW!
My head is exploding with gearlust.

Another Tax return Jojjelito?

Nope, that’s only once per year but still - guess the pay from work has to cover this one :slight_smile:
And yes, that looks about right. You could also use more original-sounding (that’s debatable I know) UA776 after an easy resistor change unless Olivier has changed the circuit.

I worked from the gain-bandwidth = f(Iset) curves from the LM4250 datasheet, so there are a few changes in the exponential converter to generate the right range of Iset.

Sounds excellent.

Sounds excellent! Any news on the MS-20 filter board, pichenettes, or is that on the back-burner now?


I was looking for a simple filter to do a “filter + BBD delay” board, and the MS20 filter was a good candidate for that, but I was waiting to try the Polivoks first. The Polivoks works better on a distortion/destruction theme, so it looks like I’ll do the MS20 with a delay.

another one for the shruthi filter bank. nice.

Well, an MS20 would also be nice but the Polivox is deliciously raw sounding!
Speaking of MS20+delay: Even Korg are doing that with their new Monotron variants so I guess the original makers likes those as well.

Next level would be Synthacon VCF with a Quadra Phaser…

Don’t get me wrong pichenettes- the Polivoks filter sounds great! I may have to sell the SSM2044 board I just bought, and get one of these new babies instead! I’m really running out of space, and, more importantly, inputs for all these boxes, unfortunately… :frowning:


yo alex…

regarding your lack of space - if you are into 19" help is on the way

Yo Frank,
Telll us more! I for one like 19" racks, table-top thingies become cumbersome once you accumulate lots of gear, Ferengi-stylee…


i dont like it cluthered with red, blue and black thingies either, but its more a long time Project coming for late 2012, regarding my actual speed of development…

Ahh, I got you! Too many projects here as well…

Two of my Shruthis will be made part of a modular synth in a 19" rack later down the road but that’s for the future as well.

That cat is disturbing.
Funnily enough, I sort of like rackmount gear, but I’ve run out of space for that, too. I’m just about to fit up a pair of nice sloping shelves for my Shruthis, and other non-rack-mounting synths. I’m instantly going to run out of space, then, too, but I should probably reconcile myself to never having all this gear going at once, anyway.


oh great. now i will have to bulid another shruthi.