System 100M VCA clone

I’ve had a bunch of Curetronic 100M PCBs for ages and done nothing with them, so finally decided to start building them up as a test for Schaeffer UV-printed panels… only because I wanted to test out my version of the OpenMusicLabs clown/clone BA662, I built a single one up on stripboard.

System 100m 130 VCA stripboard photo

For stripboarding I’ve switched to Veecad, which is much less pretty than DIY Layout Creator but at least allows for verifying the layout using a netlist exported from Kicad. Here’s the Veecad layout using a BA662 as the OTA:

Roland System 100m 130VCA stripboard layout

In case you don’t have a BA662 clone or original to hand, here’s a stripboard adaptor for a BA6110. Without any other compensation it’ll be slightly quieter than the ‘662. I measured 2.68dB difference between the two, everything else being the same.

ba662 > ba6110 adaptor

If you build the VCA, don’t be tempted to socket the transistors – I ended up frying a small pile of my clone ‘662s due to dodgy connections.

Here’s my redrawing of VCA schematic.

As for the clone (…of the clone) BA662 – the OTA part of the chip seems to work OK. The 100M VCA doesn’t use the onboard buffer, so I need to check that as well.

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121 testing testing

still not convinced tbh

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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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