Roland System 700 716 mixer clone

Roland System 700 716 mixer clone front panel

It looks good, but it’s not very good.

Don’t bother trying to make a PCB of this one, you could stripboard it in half-an-hour or less, I’d imagine. As on the original it’s tacked onto the end of the sample and hold PCB.

Notice no screws for the slide potentiometers. The slide potentiometers are bunged on a bit of veroboard (at a jaunty angle to the strips), with acrylic spacers screwed to the board and glued to the front panel using JBWeld, which is as shit as it sounds.

I had a couple of failures before I got it to stick. I’ve also tried using some special/horrific acrylic cement, which totally failed. There would be a photo of the back of it here but it’s just embarrassing.

Since then I’ve reverted to making PCBs for the slide pots, with screws in the middle of the pot throw, which works much better, and helps reinforce the front panel.


i’d rather multiple jack

710 multiple clone

OK I know, but it’s a start.

3mm acrylic is bendy, so I reinforced the back with 1.5mm aluminium to make it much stiffer, but it’s still not as solid as I’d like it.

Clone System 700 multiple from the back, showing the metal reinforcement

I should have really made the metal plate wider than I needed on one side, and bent it up to form an L-shape to totally stop the bending.

No chance for recessed jack sockets like on the original, my metal working just isn’t that good. 4.5mm panel depth is really the limit for these jack sockets, and it’s borderline for rotary pots.

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Roland System 700 705 envelope clone

705 envelope front panel

Stare lovingly, desperately at the service manual, then wake up and overlay the parts on the tracks.

Roland System 700 705 parts overlaid on traces

Draw out the circuit in Kicad from the publicly available schematics. It might be right this time, who knows.

Drawing out the schematic in Kicad

Export the net list in Orcad2 format then convert with a homebrew Java program to OsmondPCB format.

Grep out the list of parts from the Orcad2 net list and choose footprints for each part (“DIP8”, “RCR7”, “TO-92” etc) and then import all that into OsmondPCB to lay it out, using the service manual track diagram as a template:

Laying out the circuit in Osmond PCB

Use the track diagram to trace from to help eliminate any errors

Check there’s no expensive mistakes being made in the Gerber files using a handy online web tool.

Previewing Gerber files in Mayhew - front

Previewing Gerber files in Mayhew - tracks

…looks passable, anyway (shoulda annotated all the pins) – send it off to China, and then two or three weeks later –

705 boards arrive

and then nine months later, when I’ve finished doing all the not-so important things, like moving house

Roland System 700 705 ADSR envelope testing

And it worked, first time. Scarcely believable.

The published schematic actually is correct, although only one of the two envelopes is drawn out. It uses an N13T1 programmable unijunction transistor, like the System 100 and SH-5, although I reckon the 2N6027 could be used instead.

The timing capacitor is specified as a 0.33uF tantalum with a 3.3uF cap hanging off a switch for longer times, and it does get pretty clicky and tight – here’s everything set to a minimum, rise time of about 600µs.


Shorting out R101 gets us even faster, but I don’t think there’s much point:


and it all completes in just over 2ms:


Here’s a dodgy demo with some mistakenly applied Quadraverb, all System 100 with the 705 clone envelope:

And it sounds ok, yunno, although I don’t think it’s quite as good as the 100m, but that’s only going by memories ‘cos my stripboard version is buried in the loft somewhere. I’ll dig it out soon and compare – now I’ve got an oscilloscope I’m interested to try and work out why the 100m envelope is so nice.

Either way, another one off the list. I’ve put a big, possibly too optimistic order in with the ever-reliable Futurlec for a load of 30mm slide pots in the hope of recreating the 700 panels, and then hopefully I can stop dragging crocodile clips across my desktop to test a board or two at a time.