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 :)
    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… :(


  • 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...
  • Yaps…..

    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.

  • How come I didn’t know about the polyvoks?!
    Anyway this one sounds very cool :)

  • ooh very cool, love to see what you cook up!
  • Love it! I was going to transfer my SMR4 Shruthi into fcd’s programmer when it arrives, but you might just have tempted me into building a whole new kit so I can get one of these.

    Incidentally, given the number of different filter boards available now, have you reconsidered the possibility of offering kits just for the digital board (i.e. PCB and components, but without the board & components for the SMR4)? The kits are really handy for avoiding having to hunt around for components, but ending up with a whole spare SMR4 board if we want to build Shruthis with one of the other boards seems a bit wasteful…

  • I used to think the same thing about the hunt for components but I have to say it's been a good learning point (without me even appreciating it at the time) as I'm now confident on shopping about for parts.

    Anyway, love the idea of the Polivoks, I was thinking about building a clone for my modular synth but maybe I'll just hold off....
  • Oh, I went out and got all the parts for my CEM3379 board, so I know how to do it. The problem is that parts are a lot easier to get sent to some parts of the world than others. The UK seems to be a lot harder than mainland Europe or the USA – a lot of the suppliers that are the go-to guys in other countries want to charge extortionate prices for shipping, or won’t sell you stuff at all. I don’t think I’d‘ve managed to source all the parts if it wasn’t for fcd72’s help.

    Even if parts are easy to get where you are, I’m willing to bet that Olivier orders parts in sufficiently large numbers that he gets them cheaper than we could get by ordering just a handful of parts at a time. Even if Olivier did filter board kits at the same price it would cost me to get the PCB and source the parts myself, I’d be happy to pay the money for the convenience and peace-of-mind of knowing I had all the right parts arriving all at once, and Olivier would make some money on the components as well as on the PCB.

    I totally understand why people would want to source parts themselves, and I agree that it can be educational, but the other option would also be nice if it’s not too much of a logistical problem for Olivier.

  • The reason why it works on the Shruthi is that I do fairly large batches (250 kits). This makes the parts cheaper, and the kit preparation efficient (there are economies of scale here too… once I am in the resistor-strips-cutting-zombie-zone I can go on forever). I cannot be that efficient on a smaller batch.

    How much would you be ready to pay for a filter board kit?

    Keep in mind that I’m selling the parts, the PCB, but also the hours designing the thing, laying out the PCB, doing my best to answer the questions here, etc… :) I hope you understand that buying a kit from me is a different kind of transaction than getting the exact same parts from Mouser or Digikey…

  • Maybe it would be a good idea to sell the no-exotic-parts filter boards and the controller board as separate kits? As for how much I would pay, it’s hard to say but I think it would be worth a higher price not to have to shop around and to support Mutable Instruments (if that is what it is), and I certainly would be interested…

  • Hmm… expect in the SMR 4 (and the upcoming Polivoks) Filter theres nearly everywhere some vintage/hard to come by/to be harvested chip. And in the SMR-4 theres nothing your small electronic store down the road wouldnt have on stock or you could get in one single order. Thats the great thing about the Shruthi and here Olivier met his goal Keep it simple: use the simplest and most readily available parts. 100%+ percent. And if you can manage to get one of the non-standard Chips (say a CEM3379, SSM2044, IR3109 or even the CEM3399 ) then you certainly should be able to source some resistors and caps….

    Personally i think its up to us (not me again, please….) makin parts kits or providing public Reichelt Lists for the filter boards – i’d like to see Olivier makin great new gadgets rather then killing his time while in resistor-strips-cutting-zombie-mode. Or just takin a day off ;-)

  • I used to sell bags of parts (“filter board connector pack”). I removed them after a while ; first because I haven’t earned much on them (probably nothing taking into account the time preparing orders) ; and because I think it doesn’t help people understand that what I sell are unassembled products, not bags of electronic parts.

  • i alway found those packs of slightly-more-exotic parts (‘stuff that you don’t get from reichelt’) extremely helpful and wouldn’t mind paying a (moderate) premium for them. but of course it is for you to decide whether you have the time to prepare them. exciting new products (or time off) should definitely take priority over zombie work.

  • The thing that is a bugbear when sourcing the components is the strange stuff, the outliers if you will. Examples of that is the nearly standard SIP resistor pack that only Reichelt has and the power barrel connector with super skinny legs. You'll have to get them from the preferred supplier or drill the PCB slightly, plus remove a leg from a standard SIP. The Shruthi is by far better than most other stuff out there despite those minor niggles. Everything else is dead easy! Really.

    Dealing with Mouser and Digi-key is painless, the shipping cost isn't that bad. The issue is that Reichelt deals (or used to deal) with bank transfers and not credit card payments like most sensible people. This costs 10 SEK per transaction since I'm outside the euro-zone and you have to write a whole PhDs dissertation worth of addresses and what not, constantly triple-checking for errors, instead of dealing with 16 digits, a date and a CCV2.

    My wish is that the strange SIP and skinny legs barrel connector was included per PCB where used if possible. Beyond that it's fine!
  • The Polivoks filter board will use big holes for the DC connector so that the “fat legs” standard part can be used – I am going to transition the other filter boards to this if I get good feedback. 6x1 SIP networks are available from Reichelt and Mouser (and used to be available from Farnell when I started the project), so it’s not that odd.

  • If the kits just takes time from and in no way help to finance development of new products I think kits should be dropped from the shop right away. And that’s even as I have like 200 km to the nearest supplier; BOMs for Mouser, Reichelt or even Futurelec works for me…

  • Well, if I stopped producing kits, I would have no income, so it would not only mean “no more Mutable Instruments products” but also serious trouble for me (yes very soon I’ll have no other job and Shruthi-1 kits will be my sole incoming source until I have other products lined up).

    The price of the Shruthi-1 kits includes the parts, taxes, and a cut for me which accounts for kit preparation but also support and development. That’s why I talk about selling an “unassembled product” – there’s a significant part of the price which goes beyond the cost of parts and the cost of order preparation labor, because what you buy might look like a standard Mouser order, but has much more value. Now, would you be willing to pay this part if you ordered a mere “connectors pack”? My gut feeling is no, people would be pissed to pay a connectors pack 3x or 4x the price listed at Mouser, because to them it would be “just parts” — without realizing that I need a compensation for my work.

  • Then my earlier post is still valid; I like to buy kits, I like them to be separate kits for separate boards , I’m willing to pay a premium to not have to shop around and to finance Mutable Instruments’ future by doing so, and I like to support Olivier’s excellent work…

  • I just like to contribute in order to finance Mutable in any way, shape or form. Be it kits, PCBs or something else. Platypus T-shirts FTW!.
  • Im in for the T-Shirt, L please!

  • for me, it’s a coffee mug with that cute saraswati on it, please.

    and yes, i agree with lindeborg: separate kits for digi and filter boards would be great…
    (the ones based around vintage chips would be minus the vintage chip, obviously)

  • honestly, if i bought the parts in small quantities from the different suppliers (and there are parts from different sources) by myself it wouldn’t be cheaper too. your prices are cool.

  • You should probably just VST your products so people could warez them. I think your prices are fine.
  • Sorry, I think I might have confused matters with my response to thebot. I’m not asking for kits for each filter board (that would be a nightmare for you!). I’m wondering out loud how hard it would be to have an option to buy just a digital board kit. Right now if I (for instance) want to build a new Shruthi-1 with this Polivoks filter when it’s released, my options are:

    1) Buy a full kit (digital PCB+ SMR4 PCB+ parts) and a Polivoks PCB, source the Polivoks parts myself, and throw away (well, keep but not use) the SMR4 PCB and parts

    2) Buy a digital PCB and a Polivoks PCB and source all the parts myself (the digital parts are quite hard for me to find)

    I would love there to be a third option:

    3) Buy a “digital kit” (digital PCB + parts but no filter) and a Polivoks PCB, source the Polivoks parts myself but not end up with the parts and PCB for a SMR4 which I can’t use.

    To be honest if that was available I’d buy two digital kits straight away, because I’ve already got a spare assembled filter board with nothing to connect it to. It’s fine if there’s no demand for this, or if it’s too logistically difficult. I just thought that it might be a nice way to balance out the relative difficulty of sourcing digital parts given the number of different filter options.

    I’m more concerned about convenience than price – I guess the price for a “digital kit” would be €140 (full kit price) minus €15 (SMR4 PCB price) minus the cost (to you) of the SMR4 parts not included in the kit. So the money that’s factored in for your time and design skills from the full kit would still be factored into the digital kits.

  • if it’s just the trouble with finding the switches, switch caps and maybe the encoder, i can help you out. lcds are available at ebay and you should have no problems with the rest of it. in that case you could just buy the pcb and mcu.
    i guess that’s not enough, i don’t have the pots :(

  • Yo Rosch,

    Pots are these

    and Encoders that

    Yo still order daily don’t you ? ;-)

  • yes, i do!
    that’s the pot that i have, but not the ones that come with the kit. the caps won’t fit on those

  • @rosch

    I see, you need Pots for D-Type Knobs, not the stylish Moogish ones – HERETIC!!

  • D-shaft or knurled, does that even matter? Thar’s plenty of knobs to go around but if you want backlit ones your choices become somewhat constricted. I can haz moar Albs DK16-190V3 for instance, but those are pointerless so it can only be used on encoders. Hmm, I wish something was made in soft-touch material, approx. 19mm dia with a clear line for the pointer and several clear lines for encoders. Then we’d be talking LED fest! Mentor…

  • Ahem…. BACKLIT KNOBS?? WHERE?!?!?!?

  • @ Jojjelito You will never get a T18 knob on a dshaft..

    @FCD do them yourself :)

  • F****
    Honestly you did them yoursevels? Can we do a dirty trade of some kind???

  • @fcd72: Check out the action at MIDIbox.org/forums sometimes... Lots of us have back-lit knobs on our 6582's. The user Hawkeye published a kick-ass tutorial plus pixx of his very nice build, I have some construction pixx showing the knobs and LED testing in my user gallery (jojjelito there too). Altitude, soft-spoken as he is, is the grand-master of nice-looken builds!

    The Albs DK16-190V3 knob can be had in transparent clear (cf above), transparent red and transparent blue versions. Join a bulk order that's about to form why doncha?

    @altitude: Nope, it's not mix and match. But it's dead easy to get either :P Some knobs I like I even have in both so I'll just plunder the right drawer.

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