DIY stripboard Roland System 100 VCA

System 100 VCA Panel

Continuing my suddenly obsessive System 100 stripboarding with a boring bit, the voltage controlled amplifier.

System 100 102 VCA schematic

I wasn’t expecting this to be amazing sounding, being not much more than a CA3080, but I thought it was worth a go as I’m trying to replicate the original as far as I can.

Here’s the original VCA, with the blue marking on the 3080 presumably to show that it has been selected for low CV feed-through. I’ve seen circuits for matching OTAs, but I’m not clear how best to select for low CV bleed. Maybe it’s just a case of trying a bunch of 3080s to see which is the least clicky.

System 100 VCA circuitboard

I wanted to keep the mix input from the 102, so I built the thing around Q337. Also not having a TA7136 SIP opamp to hand,  I just subbed in the usual (non-inverting) TL072-based CGS DC mixer on the end, which was a mistake.

As I understand it now, the System 100 VCF inverts the signal from the VCO, and the VCA inverts it again, so it’s all back the right way up. As it stands, my layout inverts it twice, so input to the VCF eventually ends up inverted.

Incidentally I can’t imagine the TA7136 will make much difference, but now I’ve just had some arrive in the post, I’ll build a version with it.

To give an idea of my general confusion, I spent an evening wondering why the output from the VCF was crazily offset by a number of volts, before realising that this would be sorted out by the capacitor C324, which is on the VCA board. Just because it seems all nice and modularised doesn’t mean that it is.

Here’s a demo with the envelope on the System 100 101 keyboard modulating the VCA cutoff.

It gets clicky like my SH-5 with the envelope on a short release and the filter cutoff low, it might be that I need to find a better 3080.

One mod that might be interesting is to boost the input to the VCA from the VCF to see how it overdrives. Maybe messing with R378 on the input to the CA3080 might do the trick.

Here’s a stripboard layout for the inverting version using a TL071, any corrections or improvements joyfully received in the comments below, taaaa.

Update 9th Feb 2023: Corrected capacitance values on decoupling capacitors on IC305 (C325 and C326) from 100nF to 10nF – thanks Mike in the comments below.

Roland System 100 102 VCA stripboard (updated Feb 2023)

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11 comments

  1. 23rd November 2018timo says:

    thanks a lot. the system 100 and 700 are prob my favorite of all time. since I don’t have the option of buying accurate system 100 clone modules for a decent price or even at, looks like walking through the Veroboard torture chamber is my only option for getting some system 100 modules.some of the components look tooo hard to find like the u726 and other u mention. I just wish there were some slightly easier layouts with new components for the few out of production components. I wonder hw much the vca contributes to the sound of the system 100 or 700??? wish you would hae done more sound clips but thanks a lot anyways. looks like a lot of effort in these layouts.

  2. 23rd November 2018ua726 says:

    Not what you asked, but if I was going to build one thing, I’d do the 100 VCF, it sounds really fruity. I’ve briefly had that running on +/-12V, and it still sounded good, although it might need some tweaking, my test was just a quick one to see if it worked.

    I imagine the rejigged-for +/-12V 100M clone PCBs you can get would probably be near enough for the rest of it, and I think they mostly use in-production components.

    I’ve never done much mixing of stuff between the 100M/700 and the 100, but one thing I did notice was that using the 100M envelope on the 100 made it hit harder (maybe partly down to the greater output level) – but at the time I thought it lost a bit of “plucky”-ness. Tbh tho I would need to go back and record demos to be sure.

  3. 28th November 2018timo says:

    yea I have listened to the 100m manytimes and it does not move me like the system 100 but I do agree that the 100m envelope maybe a little more desirable. yea I will start off with the vcf and vca you layed out. you said the vca sounds really good. I always wondered how much the vca contributes to the sound of the system 100. I was a little bummed when I realized that frequency central is offering 100m pcbs not system 100 pcbs!. unfornate for me. im scared of your system 100 vco because of its size and expo con. but it plays a pretty big role in the sound of the system 100 I do believe. I heard a rumor that the 100m and system 100 vco are almost identical. so I will say a little prayer before comparing schematics. it would be great if they were identical or close but im doubting it.

  4. 28th November 2018ua726 says:

    I wouldn’t say the VCA is particularly special – I think it’s the VCF that makes the difference. Given a chance I’ll do a demo of the System 100 through the 100M VCA, and also one of the (Curetronic-clone) System 100M VCO through the System 100, everything is set-up for a track at that moment.

  5. 30th November 2018ua726 says:

    Done some demos of my original System 100 (not the DIY version) versus my clone 100M over here : http://ua726.co.uk/2018/11/29/100-vs-100m-clone-vca-and-vco/. Although I realise now that mine are built with clone BA662s rather than whatever OTA the FC ones are built with (probably an LM13700?) so these probably aren’t that that good a test, but anyway.

  6. 20th December 2018mercury8 says:

    and this inverted version sounds pretty good. not sure what the difference between inverted and non inverted sound wise? I have a couple th vco-1 into a ms-20 vcf. would it sound good to run a ms-20 into this inverted version? and is inverted the usual? layout looks great by the way and im thinking about building it.

  7. 20th December 2018ua726 says:

    Can’t think you’d be able to tell the difference between the normal and inverted version to be honest unless you were mixing non-inverted versions after the VCA? Never tried it with the MS20, should be ok.

    I should probably flag that someone in Japan has just started doing cheap System-100 clone PCBs – here’s the VCA version: https://www.pharmasonic.jp/shop/index.php?id_product=102&controller=product

  8. 7th February 2023Maik says:

    Hello,

    I built the VCA, it works wonderfully! Thank you for your work and for publishing!
    I only have normal sound via “Mix In” and Out, this cannot be changed on the VCA, I don’t know if that’s how it should be! But about “VCF In” and “VCA Out”, everything is great!
    I’ve tried different CA3080 “the normal ones” and the ones in the “Metaldose” from RCA, all work the same! Unfortunately there is always a small sound that I can’t get rid of, do you have any idea what could be done?

    Best regards

    Mike

  9. 7th February 2023ua726 says:

    Amazing, glad you got it working!

    On my original System 100, it seems like “mix in” is for mixing in another source (like the System 100 101) so that both sources come out of one plug, if you see what I mean – so your description sort-of sounds like how it should be.

    On the small sound that you can’t get rid of, have you tweaked the DC balance and cutoff trim pots? The service manual (full recommend, lovely drawings) is worth taking a look at it, although the VCA calibration section isn’t totally clear. From memory, the DC balance trim is about making the CV in click as small as possible, and the cutoff trim pot should enable you to cut the sound off fully. If not, check values of R386 and R382, and make sure your VCA cutoff trim pot is connected to +V and -V on either side, and also that Q335 is oriented correctly.

  10. 9th February 2023Maik says:

    Hello,

    Thanks for the feedback !
    Yes, I calibrated the trimmers according to my feelings, even if they are on a minimum, I have a QUIET basic tone! Ultimately, it doesn’t bother me, the resistances were all correct for me! I think I’ll remove MIX IN and OUT and with it the TL071, I don’t know what I could use it for.
    Thanks for the “link”, I saw in the circuit diagram that you entered 100NF for the C325, the circuit board says “.01” (10NF), but I think that’s rather unimportant, isn’t it? I have an SA733P instead of Sa733Q and an SC2240GR instead of SC1000GR, but that’s rather irrelevant! I soldered a 100NF foil to the bipolar 10UF electrolytic capacitors as a bypass.
    I’m doing a nice panel design for this useful VCA.

    I think it’s great that you created Roland stripboards like this, there aren’t any other ones on the net, valuable work from you! Would love to build your Roland VCO design but you advised against it, too bad!
    Do you offer circuit boards of any kind for the Eurorack or Kosmo for sale?

    Greetings Mike

  11. 9th February 2023ua726 says:

    Fair enough for removing the mix in and out, no point having it if it’s not useful to you.

    Also thanks for the corrections, they’re really appreciated. Like you say, they’re not terribly important as C325/C326 are used for decoupling, but I’ll update the doc.

    Any of these layouts done in DIYLC (you can tell by the graphics) were built without a netlist, or any automated checking against the schematic, so there still might be errors in the layouts.

    Your substitutions sound fine – I think I managed to get hold of some 2SC945Q a while back, don’t think there was much difference. I guess you could select for lower hFE in the -P variant.

    The stripboard Sys100 VCO was such a nightmare to get going, honestly. If you want a Roland-y VCO then there’s obviously a few 100M clones out there, I don’t feel as though the mint-green-flavoured System 100 is that much different on the VCO front.

    The 100M stuff I’ve made over the last year or two is all very much Not Eurorack Size, powered off +15/-15V, straight clones of the original boards with my own wonky versions of the front panels. Haven’t got anything for sale at the moment, but maybe I’ll get round to it.

    cheers

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