Looking to build my first VCO

DIY STUFF
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There’s dipping your toes in the water and then there’s running in screaming with your arms flailing about. I’m doing the latter.

I’m diving in head first into this and I figured instead of stumbling around in the dark and banging my toes on everything. I would just come here, try to use search, not find exactly what I need, and then make a post. Hello feel free to yell at me! :crazy_face:

I’ve done a bit of research on this after deciding I needed to build this. STUFF - LOOK MUM NO COMPUTER

CEM3340’s are cost prohibitive, AS3340’s can be bought in bulk for 1/3 the price. So good, neat! Did a bit more research found people were having issues with it, and well I feel like I done gone smacked the hornets nest. I have no clue where to go too from this point.

I am looking at varying designs and trying to figure out which one gives the best ‘bang’ for your buck, before I start doing BOMs.

Here is one such design I found.

(but looking at the comments people are having difficulties powering it with 12 volts?)

I’ll admit I’m out of my element, but I’m willing to learn and I’m committed to seeing this through.

I figured since this is well treaded ground it would be wise to tap into the collective knowledge that is available.

Some things that might be worthy to note.

I am in the USA.

1v per Octave is important to me as I do have a lovely Arturia mkII 88 Keylab that does CV out with 1v/Octave. So tuning seems like it might be important to my use case? Once again feel free to yell at me if I am incorrect.

I don’t have a lot of financial resources, so it needs to be affordable, and I am determined to build it myself. (hence why I am seeing what design I want to go with before I build it, also why else would I post into the DIY stuff if I didn’t want to DIY!?)

:bat: Hope to hear from y’all, and gain good insight! :bat:

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Welcome to the forum!

Eddy Bergman designs are always very good and well documented. I think that’s a great place to start! I see a few comments on value changes for running off +/- 12v, so make sure to read those. If you run into problems, Eddy is always super helpful. I don’t think he’s on this forum, but he’s on the “synth diy for non-engineers” Facebook group for sure.

Good luck!

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@EddyBergman does pop in from time to time!

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The more I know, awesome!

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Any reason not to try Sam’s stripboard designs? He calls for CEM3340 but the AS3340 should work fine. In principle there’s a part or two that should have a different value; in practice, it doesn’t seem to matter much. They’re designed for 12 V. And you can work your way up from a very simple version to a more fully featured one.

By the way, if you’re using the word “prohibitive” literally — if the price difference is enough to make the difference between financially possible and impossible — then be warned, synth DIY is usually more expensive than you’d think. Not as much as buying assembled and tested modules, but still — there are the builds that don’t work out and need to be discarded, there are the utility modules like mixers and multiples that you don’t think about much but turn out to be indispensible, there are power supplies (which you should never try to cheap out on), tools, patch cables, and so on. All in all the cost difference between the CEM and AS will not be very large compared to the total cost of this hobby.

There are VCO designs that don’t use a 3340 but only general purpose op amps, transistors, and such you can look into too, though their higher part count likely makes their cost about the same.

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I think the easiest way to explain it is, end goal and resources? I was going to go for the design Sam has, but after some consideration the Bergman design seems to offer more for a bit more time investment.

The following quote from Bergman’s blog post, highlights why I am considering going with his design over Sam’s simpler one.

" I used the datasheet VCO schematic for the AS3340 using the stripboard design from the LookMumNoComputer website. I could never get that VCO in tune over a wide range of octaves and I couldn’t get it to play really deep tones either. I think the fact that he left out the HF tracking had something to do with that."

I have an Arturia key lab with 88 keys so the wide range octave tuning is a primary consideration.

I found a section in the rather lengthy write up discussing the parts that need to be changed to run it on 12v, and it doesn’t look too bad.

And I see the edit.

By prohibitive I do mean quite literally. I am on a very limited currently non existent income after becoming disabled. Financially I am stable, but I need something to keep my blue collar hands busy( and try to fight off depression), and I have always wanted a physical synth, and I truly doubt I will find a proper 1980’s synth just lying on a thrift store shelf in rural America… I mean it’s theoretically possible, but those are scratch off odds.

I know how to spread out a bit of coin, which is why I am in the planning phase of figuring out what ‘modules’ I need, and then go about how to build them.

Truthfully this entire build is going to be put into one housing all together as a desktop synth. So this isn’t like Eurorack or Kosmo. Once the parts are decided that’s it. :grinning: Famous last words I know, but I am approaching this from the same angle I approached my welding gear as a tool for music, and any limitations that come along the way from my choices will just be features. :crazy_face:

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Hm, well, a (non DIY) desktop synth is what I started with. And then I decided augmenting it with a couple Eurorack modules would be good…

Anyway, point taken; but I still think if the higher price of the CEM3340 is not merely significant but prohibitive, then there’s a real chance of your whole project being derailed by contingencies. Definitely budget for more than you think you’ll need to spend.

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Hi! Welcome to the wonderful world of synth DIY :slight_smile:

Sam’s design for the 3340 ‘super simple’ vco is basically the lowest parts count he could possibly whack on a stripboard and get a usable sound out of, but it is very limited and Eddy Bergman’s designs are great - you have picked a great starting point for your synth in a 3340 VCO. It is worth noting that there are many commercial modular VCO’s that have tracking issues when you get up into the 7 octave range, so don’t let the fact that it won’t track your entire keyboard reliably put you off. A lot of DIY designs will hit 5 octaves pretty well with good calibration - I know my Kosmo #1222 performance VCO’s from Sam do.

I would like to echo a few things from analogoutput though, regarding costs. This is possibly the most expensive hobby I have and in the past few years I have easilly put £3000 (in terms of raw parts cost) into building synth modules. Had I just put it in a jar and saved it I could have bought quite a few fully fledged commercial synths (or one really high end one) by now. I have also found that I will mess up at least one of almost any module I set out to build (at least if it’s not an actual kit - kits are much easier but at a slight price premium) so always factor in spare componants. Also the tools required are more than just a soldering iron and some solder - make sure you pick up a half decent oscilliscope if you don’t already have one for instance.

What kind of synth is it you are wanting to build? You mention 1980’s in your post, but do you have an actual ‘sound’ you are going for? This is going to be a big factor in both the design, size and overall cost of the finished desktop synth.

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Of course I’m a member here. You don’t think I would miss out on a cool forum like this would you?? ^____^ :smiley:

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The man himself! Super helpful site you have there… ta for all the useful info and designs :slight_smile:

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You’re welcome mate. Hit me up if you have any questions etc. I have a little facebook group too. More details on the website :wink:

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The final destination of the sound isn’t… hmm a constructed concern I want to organically discover it, but I have been keeping an eye out for what commercial synths have to use a rough idea of what I need for components, but I will gladly take any suggestions on what modules to include in this shopping list!

And I am well aware this is a slippery slope hobby, but I am one of those bizarre people who seem able to build something for a purpose and go Yes! This is exactly what I wanted. (My es-335 clone is a prime example where it has a Floyd rose FXR and custom pickups and its built exactly the way I wanted it.)

For my CEM rationale 15$ for an individual chip isn’t bad, but if was I only going for one VCO I would just shrug and accept it, but considering AS3340 can be bought for much cheaper, and the surrounding components around it aren’t that bad and easily sourced. You can make up the difference if you’re building more than one. (heck I was debating on just buying 10 of them to have on hand and get the bulk discount.) And that’d be closer to 50$ 3 cems for 45$ or 10 AS3340s for 50$ Gives a bit of wiggle room, and more options as well as spares.

Hey its the man himself. Nice. It’s nice seeing that this is place is active. I’m used to most places I go to hang out being rather dead. :smiley: This is a delightful change of pace.

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Oh, go with the AS3340’s all day mate - I used a ‘real’ re-issue CEM and an AS clone in a pair of TH VCO maximus modules I made for my eurorack setup and they sound and perform identically (to the ear anyway) so there is no point deliberately spending more money on the CEM unless you actually need it so you can say ‘this classic synth I am servicing has actual CEM chips all throughout’. There is something to be said about actually going with the design blessed by the Curtis family - but again, you are just paying for the name.

Sound wise, organic discovery is a nice way of thinking about it, but if you want to build it as a desktop rather than a small modular you’ll want at least a feature set in your head. Do you want a monophonic bass monster, or a screaming duophonic lead, or is the major headache of true polyphony in your future (etc… etc…)

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Right, but even if you only use 5 of those 10 that’s still 5 VCOs, pretty useless without probably at least two or three each of VCFs, VCAs, and envelope generators, and then the mixers to put them together, and that’s before even thinking about noise generators, LFOs, sequencers, delays, ring modulators, sample and holds, drums… That is, if you’re talking about spending $50 on VCO chips, you’d need to spend, I dunno, maybe $1000 and up on the system they’re a part of.

So, again, if your financial situation is really tight, don’t think about bulk purchasing first; think about a definite design for the whole system, and then purchase for that.

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Analogoutput is spot on here, if you want to get the most bang for your buck then proper system planning is an absolute must. Work out what you want it to do, what features you absolutely need, what would be a nice addition, and what is just not required in your system, and then plan accordingly. Then start thinking about bulk discounts. Those AS chips are cheap enough when purchased singally anyway - and saving a few bucks on only buying what you need (with maybe a spare or two incase you blow one up) will mean you get a ‘free’ module later on.

Just as a ‘for instance’, if I wanted to build a desktop version of a ‘classic’ east coast mono-synth using an external controller, I would want as my ‘essentials’ two LFO’s, three VCO’s (or two and a ring mod), a mixer for the VCO’s, a VCF, two ADSR envelopes, and a VCA - along with some kind of routing system for the LFO’s assuming this is internally wired and not semi-modular with patch points. After that my ‘Nice to Haves’ would be an echo/delay or reverb, an overdrive, Noise and S&H, and Midi (in case my controller didn’t have native CV outs). Then since it’s for an external controller to be played as a keyboard I would ignore drums and sequencers (plus there is already a midi provision in my nice to haves which would mean I could use any old sequencer if I wanted that). With those circuits in mind I would then start looking for designs to use, and from that draw up my shopping lists.

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This is exactly why I am here and doing my due diligence.

I do want the ability to be able to play chords if I want, but I was thinking the simple tuning a few OSC’s. Pretty much what Alex ball did in his Heavy metal on synthesizer video.

But I am not as knowledgeable in this topic. We all gotta start somewhere!

Frankly it seems the synths I keep on leaning towards inspiration for features are the late 1970’s or early 80’s ones. So monophonic is fine, but duophonic might be nice.

Honestly I don’t need a whole lot of features, nor do I need the wall of sound. I have a full DAW. I just want something physical to use, and I want to make it because. Well just buying a Behringer product just doesn’t have that same feeling

I am using the ARP 2600 as a baseline of what to use… But even that is mere suggestion.

“The ARP 2600 features three VCOs, a 4-pole (24 dB/octave) Low-pass filter, a VCA, a ring modulator, sample and hold , a white/pink noise generator, microphone preamp, spring reverb, two envelope generators, and a four-octave keyboard.”

The microphone preamp, Keyboard and spring reverb are things I can strike off the list with ease. I am not looking to particularly emulate anything. What ever this unit ends up sounding like is what it sounds like, and that has a bit of ‘IT’S ALIVE!’ Frankenstein magic to it all.

The only real uncertainties are noise generator, ring modulator, and sample and hold.

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Well, since you know what you want, just start by compiling schematics for the various different circuits (after deciding on your power standard) and working out the componants you are going to need and you’ll be ready to start drawing up panel layouts and working out your shopping list(s).

The biggest expense you can cut (if you want to keep prices down) is the modular nature of the synth. If you go with internal wiring and remove the panel sockets you’ll save a significant chunk of change - but in turn lose a lot of flexability. But this is a ‘personal preference’ affair - I would keep the sockets myself.

Just chip away at the project piece by piece - checking each circuit as you go - and you’ll be golden.

Oh, and don’t forget to include something to convert the internal signal level to line level, otherwise you might damage any audio interface or amp you plug into - synth level tends to be too hot for most devices without some protection.

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The 2600 also had an envelope follower, a voltage processor section, and line level and headphone outputs. The original did not have MIDI capability of course, but it would have if MIDI had existed. Post 1974 the keyboard included an LFO (in addition to the switchable LFO mode of each of the three VCOs) and portamento.

You can buy a complete kit of parts to build a 2600 replica, sans keyboard (and LFO and portamento), without MIDI, for $1949. I mention this not because I think you should buy it — or should you? I’d love to see someone here tackle it! — but as an indicator of how much a DIY 2600-equivalent would cost. That’s on the high side since sourcing your own parts is almost always cheaper, and it includes a case which you could definitely replace with a cheaper homemade one. But on the other hand, you’d need to add either MIDI and a MIDI keyboard or a CV keyboard.

Basing your planning on an existing system is a good idea. I’ve drawn my inspiration for my recent builds from the Moog Model 15, which in terms of subsystems and resultant capabilities was a step or two below the 2600. The above linked site, as well as synthmuseum.com and vintagesynth.com, are good places to look for ideas.

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I hadn’t realised that they had done a new run on the TTSH… god I wish I could afford to just drop that kind of money in one go.

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Just to come back to the VCOs, I made 1 with a CEM (my 1st) and since 4 or 5 with AS and no problem with, and honestly for me no difference in sound, stability or other, apart from the price :slight_smile:

In my case, I think I spend around 200 to 300 euros per case (for around 19 modules).
But the more time passes the more the price of my boxes increases, the modules are more compact therefore more components (duals or triples instead of single)

As said @analogoutput removing the possibilities of patch cables may be economical but will limit the possibilities, but something like this project maybe can interesting you

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