Roland System 700 707 amplifier/integrator/envelope follower clone
Argh, PCB is dated Dec 2015, it’s been a while… three simple circuits for the price of one on this board, which you should easily be able to stripboard. Here’s my version of the schematic – R3 has no value specified on the schematic, but the board overview in the service manual (and Yves Usson’s photo of the board) has it as 1K.
Here’s a video demo of the envelope follower, using the drum loop from “being boiled” as the followed signal, with the env follower output going to the System 100 envelope input socket. See how the red light goes on and off!
I’ve never found much use for envelope followers but maybe I’m not just creative enough with them. If the signal volume on the input gets boosted enough it bleeds through to the output, but at a normal sort of level there’s no problem.
The integrator works fine, but with the specified values when using it as a CV slew for a VCO it needs a fine touch to dial in the right amount. I used a CA3140 instead of the specified (ICL?) 8007.
The amplifier does the amplification thing as you might expect, and could be really useful (although I regret not putting a switch on the panel for DC coupling).
Also made a mistake on the panel – it should be E.F. on the switched input for the integrator. Had to correct the spelling of “integrater” too, couldn’t let that stand.
…and round the back – aluminium bent up at the edges to try and stiffen the panel, though it’s not so bad at this smaller size.
I’ve got better at arranging the board-to-panel wires since I did this, it looks a bit higgledy-piggledy.