Roland System 700 707 amplifier/integrator/envelope follower clone

Roland System 700 707 preamp 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.

Roland System 700 707 clone module

…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.

Roland System 700 707 clone round the back

I’ve got better at arranging the board-to-panel wires since I did this, it looks a bit higgledy-piggledy.

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blueshift dim-c clone

Done done done. I made the holes for the switches a bit too big, might need some bigger washers.

Aion Blueshift boxed

Really boring round the back, it’s pretty tight.

Aion Blueshift inside back

Inside! it’s packed out. If I’d’ve designed this board it would’ve ended up about two feet square.

Aion Blueshift inside

If you’re going to build it, use the specified capacitors – the ones I used were too tall, although I’ve just about got away with it.

I’ve recorded some basic demos just to get an idea of what the Blueshift does to a source.

Here’s the Blueshift on DC power (hence the hum, unfortunately) having a simple polyphonic JX3P sequence shoved through it while I flip the switches at random. See if you can tell when I turn the Blueshift on:

And here’s another one on battery power, first section no effect:

It seems like it’s very shy of higher levels – I had to notch the JX3P down to its “M” output level to avoid distortion, and like I say, it seems to hum with the DC adaptors I’ve got, although I don’t necessarily trust any of them.

But I really like the way it sounds, and it can do exactly what I wanted, which is to widen a mono source without sounding too obviously swooshy and chorused.

The pedal format isn’t really ideal in my studio but I just wanted to get it done. I’ll pretend now that I could make it into a half-rack or something, but that won’t ever happen.

It’s so nice I’m tempted to have a look at making a more rack/studio-ish Dimension-D-type thing, maybe J├╝rgen Haible’s Subtle Chorus or something. But this will do for now.

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LED indicator noise in System 700

I’ve never been able to get the LED indicators to work well in any of the System 700 circuits I’d made. Even with no input, the green light would stay on and horrific screechy noise would get injected into the output.

Vowing to finally get it sorted out I connected up my 703E VCF clone, got the expected horrible noise and stuck my oscilloscope on the +14.4V LED power line. It showed that the power line was oscillating at about 32MHz, at an amplitude of about 200mV.

Then I tried some stuff like bunging different capacitors on the LED power line and different power supplies, but nothing did the trick.

Some of the schematics suggest that CD4001AE is the right version of the IC to use, although confusingly, not all of them. Also all the pictures of the boards I’d seen have AE or UBE versions of the 4001 in place. Found some old RCA AE variant chips on eBay and gave them a go:

CD4001AE in the 703E filter

DAMMIT IT WORKS.

I wasn’t keen on relying on 35+ year old CMOS chips, so I ordered a few 4001UBE, and they work too.

Mystery solved, put the kettle on.

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