We live in interesting times. For many years, people have been wondering if it would be possible to reproduce the old CEM (Curtis Electro Music) and SSM (Solid State Music) chip designs from the late 1970’s and early 80’s. We’ve always been told that there wasn’t enough interest to make such a thing commercially viable, or that the start-up costs of setting up a design ran into millions or hundreds of thousands of dollars that you’d be highly unlikely to ever see again, or even that those chips were based on obsolete technology and that converting the designs to modern fabrication methods would be prohibitively expensively. For one reason or another (but mostly money!) it was always impossible. But no-one ever stopped wishing that one day those chips would come back. Now, I don’t know what’s changed, but suddenly everyone is back in the game.
New production analog synth chips
There are four companies currently producing analog synth chips. Sound Semiconductor and OnChip are what remains of SSM and CEM respectively, and CoolAudio and Alfa Rpar are the new kids on the block. Here’s what they’re making in January 2018.
SSI2144, an improved version of the SSM2044 filter chip with reduced control feedthrough and some other tweaks.
SSI2164, a clone of the SSM2164 quad VCA chip (coming soon)
Curtis Electromusic / OnChip
CEM3340 Rev. G oscillator. This is the original chip, as far as anyone can tell.
They changed it to “Rev. G” only because they actually downgraded the spec slightly in one regard – the original chip claimed it could run down to a +10V supply, but apparently this was not universally true, so the Rev.G specification is more realistic. If I understand it right, the underlying chip hasn’t changed, only the spec.
AS3310 voltage controlled ADSR envelope generator
AS3320 voltage controlled lowpass filter
AS3330 dual log/lin VCA (coming soon)
AS3340 and AS3345 oscillators
AS3360 dual log/lin VCA
All of these are clones of the respective CEM chips with the same numbers. Like the Sound Semiconductor chips, these have had one or two tweaks to fix obvious flaws in the original designs and to take advantage of newer technology, but they’re pin-for-pin compatible and sound as good or better than the originals.
These folks are the ones to watch! They’re turning up with new (old!) stuff at an impressive rate, and the chips seem excellent. Electric Druid have a good relationship wth the company, and we’re going to keep a close eye on what they come up with next.
V3340 oscillator, clone of the CEM3340.
V3320 filter, clone of the CEM3320
V2164, clone of the SSM2164 quad VCA
V13700, clone of the LM13700 dual OTA
CoolAudio have been cloning a lot of other old stuff for ages – BBD delay lines (V3207, V3208) and companders (V571) for example.
So what happened?
Well, I’m not sure, but I’ve been following the story and I can fill you in on some of that. In 2016, Uli Behringer announced that they were thinking of recreating some of the original synth chip designs, and that the CEM3340 oscillator was likely to be the first. Behringer’s semiconductor production is set up as a separate company, CoolAudio Semiconductor, so the new chip would be a CoolAudio product. Curtis Electromusic (CEM) had been having similar thoughts themselves, and the possibility of being beaten to market by a clone spurred them on to get on with it and the CEM3340 Rev. G was the first of the new wave of analog chips to hit the market. This was followed shortly after by CoolAudio’s V3340. This was the first crack in the dam. The next to appear was a collaboration between Erica Synths in Latvia and Alfa Rpar, a local chip fabricator based in Riga. They turned up with the AS3320, a clone of the CEM3320 filter featured in the Sequential Pro-One amongst many other classic synths. By this point the floodgates are open! We’ve had recent announcements that Solid State Music (SSM) are being reformed as “Sound Semiconductor” and their first product is an improved version of the classic SSM2044 filter now known as the SSI2144. I was pleased to note that they’re aiming for an improved product not a perfect clone. The resonance response on the original was far from ideal, and the control feedthrough could definitely use improvement – both of these issues have been addressed to some extent. I haven’t got hold of the chips for testing in the workshop yet, so I can’t report on how well they’ve done, but “better than the original” sounds like an excellent chip to me. They’re also thinking of producing a version of the SSM2164, the SSI2164. I await developments there with interest, and I hear that they’ve fixed a problem in the original chip which causes it to self-destruct if the negative supply is removed. That’s not a big thing, but it’s a welcome improvement.
Meanwhile, back in Latvia, no-one sleeps apparently since they must have been working flat out, and have turned up with versions of the CEM3310 envelope generator (AS3310) and their own take on the CEM3340, the AS3340. The AS3360 dual lin/log VCA was the most recent chip, but the more versatile AS3330 dual lin/log VCa is also in the pipeline. Like Sound Semiconductor, Alfa have made one or two tweaks to the designs to improve minor technical issues or other problems. However, currently Alfa are the only company who can provide a full set of synth chips (VCOs, VCFs, VCAs, and ADSRs). The others have some catching up to do!
Who’d have thought a few years ago that by 2017 we’d be in a situation were there was not one but three different sources for the 3340 VCO chip?! It’s extraordinary! Doug Curtis is either rolling in his grave or whooping and hollering at his post-mortem success! Either way, his impressive legacy is in no danger for the time being.
Cool, can I grab a few?
Absolutely! Knock yourself out! If you’re like me, you’re a kid in the synth candy store! Currently we have the following chips in stock:
- Curtis Electromusic CEM3340 Rev. G oscillator
- Alfa AS3310 envelope generator
- Alfa AS3320 filter
- Alfa AS3340 oscillator
- Alfa AS3360 dual log/lin VCA
- CoolAudio V3340 oscillator
- CoolAudio V2164 quad VCA
- CoolAudio V571 Compander
These are all 0.1″ DIP format chips, which makes for easy breadboarding and experimenting. Enjoy!
Update January 2018
This article was originally posted in October 2017, but I’ve kept updating it to include new chips as they’re released, and I’ll continue to do this when something relevant happens. If anyone has any experiences to share using these new chips, I’d be fascinated to hear – please make a comment below.