CEM3379 alternatives?

So I’m about ready to start building a Struti-1 (gotten impatient waithing for struthi, plus I just like having the first gen). But before I order a batch of components I want to make sure I’ll be able to get everything I need, and of course it all comes down to this chip. Are there any alternatives out there that I can use in its place without having to rewire the whole system? Will the 3378 work instead? Or are there still places around where you can actually get one of these things??

Any information is greatly appreciated!


Hi David,
no alternative, you need 3379 and you can find them in vintageplanet.nl

Yo David,

no, the 3378 wont work directly (they both have a different output stage http://www.synthdiy.com/files/2004/c3378pdf.pdf, the filter is the same…) but maybe you can make an adapter. DOEPFER has some 3379 on stock (although expensive…)

Edit: Just checked: as Olivier points out you will have to do an adaptor board, in the original schematics the filter output (pin11) goes thru the output pan mixer (in at 16 and out at 17 - maybe you can rebuild this piece of the chip with an OpAmp chip…

Edit2: if you have a source for 3378, please let me know, i might want to try the adaptor board thing

The 3379 can no longer be found at vintageplanet.nl . It looks like Doepfer still has some, for 40 euros (ouch!). The 3378 is not pin compatible, you’ll need to build a small adaptation board and change some components values.

Anyway, may I know why you prefer to build the first version? The Shruthi-1 is more compact (despite the bigger boards), has a more complete OS (sequencer, more oscillator options), and more patch memory. Since there’s some space left on the chip there’ll be more firmware evolutions.

If you’re worried about the fact that it’s all new… There has been so far 2 (out of 2) successful builds besides my prototypes. And maybe 3 soon as I’ll get a new tester in the loop!

If you’re looking for a third tester i’d like to be in the loop :slight_smile:

Just what i can say: this fuc*$*ù Shruthi-1 sounding goooooooddddddddddd I will try to make a little vidz toonight!

Wow didn’t expect so many responses this quickly!

@pichenettes: as I said, really I’m just impatient and overeager to have one of these synths in my hand. Plus I like the idea of having the first Gen that only a handful of people have gotten to use. Perhaps those are silly reasons but that’s the honest truth. If it turns out I wont be able to do it for a reasonable investment I will likely just sit and wait for the new one to come out.

@fcd72: I do not have a specific source for the 3378, I was simply asking because I know the chips are similar and that one is slightly easier to find. Sorry to disappoint!

@ WillyyDavidK

If you find some 3378, get one for me 2 - in curious. If not, maybe the SRM4-Board might fit? Just kiddin…

Alright guys I’m happy to say I actually managed to track down a Guy who still had an extra 3379 lying around. Now that I’ve got a source for everything, it really comes down to PCBs. How do I go about getting a set?

Also, approximately how long do you think it will be until struthi kits are available? I may just hold on to the chip for a little while and wait for the new design if its almost ready, since I can still use it in the new filter board.

Olivier recently mentioned that we’re probably 2-3 weeks out…

Regarding the boards: you can generate Gerber files from the Eagle files, and submit them to BatchPCB. It’s relatively cheap ($30 per board), easy to order (the process is friendly and you see a preview of how they “parse” your Gerbers), and the boards are made by GoldPhoenix, so the quality is good. The only problem is that it can take up to 3 weeks because they bundle several orders on a single large panel.

I can also get reprints of the Shruti-1 boards in small quantities for a very reasonable price (about $15 per board), but it’s worth it only if I do this along with a more expensive order. I’ll have a bunch of Shruthi-1 boards redone + the SSM2044 board done within 2-3 weeks. I can reorder a small quantity of Shruti-1 boards at this moment.

Regarding the Shruthi-1 kits, I know it can look annoying given that everything seems ready, but I’m ramping up one tester at a time.

So it looks like whichever method I choose I’m still looking at 2-3 weeks to get the boards? Would etching my own be possible? The boards are 2 layered, correct? Could I use a board and draw out the circuits, one layer on each side, with conductive ink?

If making my own isn’t possible and ill still end up waiting a few weeks to have the boards made I’ll probably just order the new ones from you, since they would get here at the same time anyways.

If you have the equipment to do so, you can obviously do the boards yourself. The minimum trace width is 10 mil, so make sure first that you can work reliably with this width!

Well I don’t have any specialized equipment, but I can pick up what I need from fry’s. Would it be possible to draw the traces in by hand using a trace pen and following a printout of the eagle files? Or would the toner transfer method work?

I have no experience with etching PCBs at home. Try printing the traces at a 1:1 scale and see if it looks like something you could do reliably with a trace pen.

Personally I wouldn’t use a PCB without soldermask in a finished product - it’s just begging for problems.

Alright so I ordered the 3379. Interestingly enough, I bought it from a guy named Kevin who actually said he sold a few of the chips to you back when you were putting the first kits together. I managed to nab his last one!

Anyways, more and more I’m thinking I should just wait a few weeks for the first run of the shruthi to come out. Will you be making any of the 3379 filter boards when you put in your order for all the pcbs? If not, would you mind putting one in special for me, and I’ll give you the extra 15 bucks? In the meantime I can order the components for the filter board since I know you aren’t making kits for them.

I also have a random question about ordering components. The BOM doesn’t list voltages for the caps but when I look up the part numbers listed in digikey it says they are 100V. Is it necessary to match this if I’m ordering elsewhere, or is it possible to mix with, say, a 50V cap? Do you have to scale the cap value when the voltage changes or something? Sorry if this is a dumb question, I’m still learning about electronics.

I had 30 CEM3379 filter boards already made – I have assembled and tested one - no problem. Being able to trim the cutoff range is great!

I was thinking about selling “half-kits” containing only the parts for the digital board, but then, if you’re going to source components for the filter board you could purchase as well components for the digital board, and having to desynchronize the purchase of parts for the two halves is a mess. However, to make things easier I will sell programmed ATMega644p/eeproms, PCBs for the digital board, and LCD modules.

Capacitor breakdown voltage is not an issue for this kind of circuits. This parameter has no influence on the normal operation of the capacitor - it’s just telling above which voltage the capacitor will explode. Just make sure it’s above 30V (16V for the tantalum cap near the LT1054, since tantalum caps get more expensive as the breakdown voltage increase). You can mix different values. You don’t need to scale the cap value.

the cap values are max ratings. so, as all voltages in the Shruti are below +/- 5V you can literally use all common types, likeanything above e.g. 25V is always a safe choice value in that range.
but it’s really worth to have a look at the pin spacing of each original component, as the boards have been designed JUST RIGHT for the parts on the list. that means if you stick to the given footprint you won’t have to bend any legs (except for resistors, obviously).

regarding the boards: given that you have to order parts and wait for them anyways and regarding the quality of the original boards waiting for Olivier’s is surely the best choice. but if you need them as immediately as possible you can e.g. give the eagle files to PCB Mike (the guy who does the german midibox kits store) and have him make them for you. afaik he offers 24h service (better ask). of course you’d have to pay for the repro film also. actually the only benefit would be the instant access.

for the filter chip you can also try this guy at
good luck!

Thanks for the polite responses, sometimes the simplest bits of information are still hard to figure out online unless you just ask someone.

@pichenettes: could I buy one of those filter boards off of you? Do they work as a standalone filter with no tone generator? That would give me something to play with while I wait for the rest to become available lol. My 3379 is in the mail on its way to me as we speak and I’m preparing orders for the rest of the components from a few different sites to see who has the best prices. Also, if You decide you don’t want to mess with the ‘half kits’ I’ll still be interested in getting the PCB and possibly the pre-baked atmega and LCD as well. Can an empty chip be baked using sysex or is that a function of the firmware? If not you just need to cut a serial cable and wire it to the tx pins, correct?

The PCB for the Shruthi-1 CEM3379 filter will be sold at the same time as the kits. It wouldn’t be fair to the people waiting for the release of the kits if you cut the line. Also, I’m trying to rationalize a bit my processes (inventory, billing, etc)…

The board can work as a standalone filter - just send an audio signal on the audio input (or on the >OSC pin), and 0-5V CV signals for cutoff / resonance / VCA gain.

An empty chip from Farnell or Digikey has no bootloader allowing firmware update by SysEx or by serial port. It is not even set for running on an external crystal! The instructions for “boostrapping” a blank chip are detailed on this page.

You need an AVR programmer to do that.