100 vs 100M (clone) VCA and VCO

system 100 vs 100m clone fite

Prompted by a comment on my System 100 VCA stripboard post, for as much use as it is here’s a very quick comparison of the original System 100 VCA and a clone System 100M VCA, built on stripboard with a BA662 clone for the OTA.

No envelope tweaking, just a bit of VCF variation from CV2 on the MC-4, and then full-gas into whichever VCA.

Here’s the stripboard clone 100M VCA, behold:

100M clone stripboard VCA

This is the (non-clone) System 100-only demo:

And this is the System 100 played through the clone 100M VCA (set on linear response), using the System 100 envelope as a CV source.

The System 100 has a lower output envelope than the 100M, so the 100M VCA is super-quiet when triggered from the 100 when set to exponential response. Flipping the VCA to linear gives you a usable audio level to play with.

The VCOs in my 100M clone are a couple of Curetronic boards, both using a heated CA3046 in place of the ua726. I’m not convinced the scaling is totally right on either VCO, so try and ignore that. Here’s a quick test of the VCO waveforms played through the System 100 VCF and VCA. You’ll hear:

  1. System 100 square, low VCF, mid res
  2. 100M square, low VCF, mid res
  3. System 100 sawtooth, low VCF, mid res
  4. 100M sawtooth, low VCF, mid res
  5. System 100 PWM’d square, open VCF
  6. 100M square, open VCF
  7. System 100 sawtooth, open VCF
  8. 100M sawtooth, open VCF

and if you can take it, here are some sweeps, 100 then 100m, in the order

  1. sawtooth
  2. square
  3. PWM square
  4. triangle wave

That’s too much excitement for now, I’m going for a lie down.

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System 100 VCF mystery solved

Alright, not much of a mystery, but have been drawing up some new PCBs over Christmas and wanted to check something on the System 100 (not M) VCF – the original schematic specified a dual 100KA for the resonance potentiometer, but I always suspected it suited a reverse audio pot better.

Here’s a picture from my 102, with the panel flipped down in front of me (so top here is bottom of the panel, just to make it confusing)

System 100 VCF pot orientation

Check the orientation of the embossed numbers on the back of the pots, and compare the (upside down) resonance and HPF pots against the right-way up mixer section (RM, VCO and Ext.).

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Roland System 100 brochure

Roland System 100 brochure

Ages ago I’d read that there were originally going to be more modules in the original Roland System 100 series, but nothing further was released (probably in Gordon Reid’s excellent History of Roland)

I hadn’t seen anything more about this until I spotted this brochure on eBay (long gone now) for the original units, with the following:

Also planned for the near future are: Audio Delay unit, Stereo Phaser, VCO bank, and other units.

…so maybe, 105 Audio Delay, 106 Stereo Phaser and 107 VCO Bank?

I could imagine the delay and the phaser being similar circuits to the equivalents in the 700, but I can’t think how they would have been designed to stack up on the System 100 – the top of the 102 isn’t particularly deep. Maybe this was part of the reasoning that led them to design the 100m?

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