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Kassutronics VCO 3340 (eurorack)
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2, 3, 4  Next [all]
Author Kassutronics VCO 3340 (eurorack)
kassu
Status 2-Aug-2018: PCBs and panels are in stock.
I'm out of AS3340, but it's available from Erica Synths, Thonk, Electric Druid, Musikding, Modular Addict, Cabintech, and probably others.

Pricing:
PCB: €6.00
Panel: €7.00

Postage:
Europe: 1 set €3.00, 2-4 sets €4.00
Rest of the world: 1 set €4.00, 2-4 sets €8.00
The boards will ship as normal priority letter, no tracking. Ask me if you need other options.

How to order:
Please send your order to kassutronics at gmail dot com. Please let me know the country of shipping so I can calculate the shipping costs correctly. I will send you a paypal invoice, and ship after receiving the payment. If you prefer to pay by bank transfer (EU only), let me know.

Documentation:
The complete documentation can be found on my blog: https://kassu2000.blogspot.com/2018/06/vco-3340.html

Some pictures of the final product:

Completed module:


Close-up of plywood panel (newer version with white background):

Note: The panels are shipped with protective tape on both sides. Peel off the tape to reveal the actual printed surface!

============= Original post ===============
Hi,

I recently designed a basic VCO around the AS3340, which is a clone of the CEM3340 VCO chip. Locally (in Finland) there was some interest in the design, so I decided to make a second revision and do a small run of boards. I offer it here also in case people are interested. The goal of the design was to have an easy to build, affordable VCO with good tracking and all the traditional waveforms. The resulting module follows the datasheet circuit fairly closely, plus output scaling/offsetting and a JFET triangle-to-sine converter. Everything is throughhole, but still fits on a single PCB.



Features:
- Pulse, Saw, Triange and Sine outputs
- Big frequency knob + fine-tune knob.
- PWM knob, serves as attenuator for PWM input or as pulse width control when no PWM is connected
- Exponential (V/Oct) and linear FM
- Switchable hard and soft sync (as they are implemented in the chip, different from the traditional hard sync)
- 9mm pots, thonkiconn jacks and all THT components* on a single PCB
- 8hp eurorack, current draw +12V XXX mA, -12V XXX mA typical

Short demo video: https://www.youtube.com/watch?v=5rmUaaMWEd8

* For the J201 JFET there are both THT and SMD pads, since the THT version is no longer produced. It is however still available through Ebay etc and maybe (currently out of stock) from Tayda.

I will also buy a batch of AS3340 chips straight for the factory, and can offer them for a reasonable price if you buy the PCB.

Panels: For my own system I use 2mm plywood panels, which laser cut at the local library. You can see how they look in the Youtube video above. If there is reasonable interest (at least 15 panels) I can get a batch of plywood panels made. They would be printed, black text on white background, rather than engraved as in my own system. The text should be a bit clearer, but this is the first time I am trying the printed option so no hard guarantee. They will be made in Helsinki from Finnish birch plywood. In my experience the panels are pretty sturdy, and once the module is assembled the whole thing is rigid. (I know wood panels are not everyone's favorite, but I like them a lot which is why I prefer to offer this over PCB panels). Of course the panel design will be also available as PDF for those who prefer DIY.
Swyndger
Yes, I would be interested in one, maybe two sets (panel, pcb and chip) ... you can never have to much VCOs wink
masterofstuff124
this looks awesome. Im in for one complete set.

thanks for sharing!
kreiff
I'm in for one set!
csaban
I'm in for a complete set!
mtts
I'm in for one set!
Jarno
Looks great, I am working on a 3340 VCO as well, but I am actually surprised how many parts it still needs for a complete VCO, and I am having great trouble fitting it on a parallel mount PCB (think I am on 10 or 12HP/TE now).

Nice job! Pretty compact and everything TH.
kassu
Thanks! Indeed, it was not too easy to fit, but that made it a nice design challenge smile. If you look closely there are even resistors between the jacks. Also I use the smaller 1/8W resistors with 0.2 inch pitch footprints (usual for 1/4W resistors is 0.3 inch), otherwise it would not work out.

A lot of space goes just to scaling and offsetting the outputs. I think these chips were really designed for making a complete synth, not modulars. If there is the typical fixed routing from VCO -> mixer -> VCF, you can just do the scaling with a different resistor value for each mixer input, and of course you could do the offsetting just with AC coupling. In the modular world we want DC coupled outputs and standard output levels which needs the extra opamps and a fair number of resistors.
Silesius
This is exactly what I need for my 3 vco monosynth! I had started to build the vco's in stripboard because I needed them compact. And all the other 3340 projects come with several pcb's, or are smd, or you can't avoid buying a front panel... I can adapt these perfectly for my project (that's why I like Barton projects as well).
So I'm in for 4 pcb's (one extra just in case) smile
SmartBits
Nice job, I'm in for 3x PCB + 3x AS3340!
Can 1/4W resistors also be used, standing? How good is the tracking?
euromorcego
i am certainly interested! 2 sets or so (best with panel).
cikl
This looks great! I'm in for one complete set.
kassu
SmartBits wrote:
Nice job, I'm in for 3x PCB + 3x AS3340!
Can 1/4W resistors also be used, standing? How good is the tracking?


Yes, 1/4W resitors can be used standing.

I have not measured the tracking in absolute numbers yet. When tuning (V/Oct tuning and high frequency track) I found I can get it to track well over the full piano keyboard range, so 7 octaves or so. I think the largest error was somewhere around 5-10 cents (a few tenth of a percent) at most. At frequencies above 5kHz the HF track started to overcompensate. Maybe I will do more precise measurements at some point.
autodafe
I still have a couple of orignal CEM 3340 lying around. Can these be used as well? or is it better suited with the AS3340 clone?
Cablebasher
Hey KaSSU

Great build. I think this is the smallest eurorack CEM VCO so far (thats through hole)

And it sounds great.

A quick question:

Do all the waveforms shift in pitch slightly when the change the pulse width?

I (and others) have noticed this on a few of the other DIY CEM VCOs and was wondering if its just a feature of the chips.

Sorry for going slightly off topic.

cheers
kassu
autodafe wrote:
I still have a couple of orignal CEM 3340 lying around. Can these be used as well? or is it better suited with the AS3340 clone?


I have only tested the AS clone, but it should work just fine with real CEMs, old or new reissue.
kassu
Cablebasher wrote:
Hey KaSSU

Great build. I think this is the smallest eurorack CEM VCO so far (thats through hole)

And it sounds great.

A quick question:

Do all the waveforms shift in pitch slightly when the change the pulse width?

I (and others) have noticed this on a few of the other DIY CEM VCOs and was wondering if its just a feature of the chips.

Sorry for going slightly off topic.

cheers


No problem smile. I have not noticed this issue, but I will have a listen tonight.
kassu
I tested it out and indeed there is a very slight effect of the PWM on the frequency. I can only hear it when I beat two oscillators together, the difference is maybe 1Hz. How strong of an effect are you seeing? I guess it is a feature of the chip.
sixty_n
looks nice, in for one perhaps two (pcb, panel, chip)
donpachi
Three full sets for me, please.
autodafe
count me in for 3xPCB + 3xAS3340
(sorry I don't like wooden panels that much...)
ntrm
1 PCB and chip, please.
Cablebasher
Hey Kassu

Thanks for looking into the pulsewidth issue.

On My VCO maximus build, the pulse width knob changes the frequency by half a semitone so very noticeable.

It is also mentioned as an issue on the TIMO pcb build as well.

I guess the issue is with a Cem3340 but each implementation has a different level of effect.

Good luck with the module.

Cheers .
Silesius
I'm having second thoughts about this after all the comments regarding the pw issue (in all 3340 builds). My plan was to build a 3 vco keyboard monosynth and one of my primary concerns is pitch stability. That was the reason I chose a 3340 design, because I thought they were known for stability and good tracking.

So, how bad is this? For example, what happens if I want to have two (or three) tuned vco's with slow lfo's modulating their pulse widths? Would they stay in tune? What happens if I have a carefully tuned two vco bassline and I accidentally touch the pw knob? Would they go out of tune?

Things like half semitone are quite unacceptable if you want to play in tune. It's difficult enough to have three analog vco's playing nicely together. Having to worry about this pw thing could be too much for me...
Jarno
If you are dead set on having PWM, you could do a little add-on board which creates a PWM pulse from the triangle output, that way you separate the PWM from the 3340.
The VCO from the Thomas Henry book "a synth for the 21st century" has a circuit like that, two opamp stages and a handful of resistors.
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