System 700 711 output module clone-ish

I’ve had this board hanging around for…about three years? That’s how excited I am by it. This is an old photo, ‘cos it currently has about an inch of dust on it.

It’s all a bit kind of just OK – the phase shifter is alright, the spring reverb is nothing special (nowhere near as nice as the Tombola spring board) and the test oscillator is my own version and that sounds… acceptable, as far as a test oscillator goes.

For the spring, I replaced the TA7136AP with a stripboard adaptor using a TL071 and kept everything else the same, as far as possible.

There’s no specification for the reverb tank as far as I can see, so I can only guess Roland used the Z-3F tank they used in the Space Echo and System 100 103 mixer. Somewhere I’d seen suggested that the Accutronics 8AB2D1A would do the trick, so that’s what I’m using.

I did some underwhelming demos at the time – here’s a familiar-sounding bassline going through the spring:

And a blippy-ish loop, starting from dry:

For the phaser I roughly matched the 2SK30A FETs as far as I was able to using the method outlined by RG Keen in JFET Matching for Effects. They’re not super-cheap, so it’s expensive to buy loads just to match eight.

These demos might be an even greater test of your patience – hold on: here’s some twiddling with white noise:

And here’s an annoying loopy bassline, first with the resonance turned down, then turned up:

For the 1KHz and the A octave test oscillators I couldn’t find any of the large variable inductors, so I went with a couple of phase shift oscillators with a bit of extra simple RC filtering afterwards.

The octave divider chip is an LM3216 – at the time I designed the board, this was fairly rare (£12 from Little Diode), so to avoid using a sought-after IC for such an unexciting purpose I designed the octave divider around the CD4024.

I say “designed”, I probably nicked it from somewhere.

Here’s a sample of the 1KHz test tone – three seconds is as much as I can take

Looking at the spectrum analysis the odd harmonics are accentuated, so I guess it’s a bit squarer than it should be, but it’s OK.

The board still needs a front-panel, and I’ve spent way too long trying to work out whether it’s worth doing a PCB or just a stripboard for the mixer section.

Either way, it’s the summer and while it’s not piddling down or throwing a gale I’ll be out riding my bike.

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Roland System 100M noise/S&H/ring modulator

100M 150 noise/s+h/ring mod stripboard

Out of all the various dodgy looking stripboards in my 100M clone, this one turned out the best (let’s just not mention the LFOs, they were a pain in the arse).

Determined to get it going first time, I made sure I’d done all the cuts, checked for shorts between tracks, powered up the board without ICs – was generally super careful, and then only later found that I’d missed out a couple of capacitors. Silly.

I made a daft mistake with the hold in the sample and hold. It worked, but the held voltage was drifting downwards rather quickly. Compared it to my System 700 board and realised my mistake – I’d used a 2.2nF (222) capacitor rather than the specified 22nF (223).

(Actually I was tempted to use System 700 boards rather than faffing with stripboard, but they’re so lazily massive that they didn’t fit in the panel space I’d designed).

I compared the white noise to the pink, and the white noise just sounded really quiet. Which is weird because it’s coming out of the same place, it’s just being filtered differently. Here’s the relevant bit of the schematic.

Roland System 100m noise circuit

I compared the outputs on the oscilloscope – didn’t take a photo, but the white noise was chopped off at 0V, whilst the pink danced around both sides of the ground point as you’d expect.

Anyway, it’s pretty obvious from looking at the schematic that the R31 (attached to the transistor output buffer, Q4) should be connected to -15V, and the track layout bears that out.

100M noise track layout

The ring mod is based on the LM1496 like the rest of the Rolands, and you’ve probably got three of those already, but anyway.

Here’s a tiny demo of clanking and white noise twiddling. The ring mod was in better calibration when I put it together, it’s bleeding a bit from one side at the moment.

There would be a demo of the sample and hold, but I’m presuming the lag pot has disconnected itself behind the panel, as it’s verrrrrrry smoooothed ouuut, barely even recognisable as a sample and hold right now.

Here’s the layout, and wonky BOM.

Roland System 100M 150 noise/S&H/ring mod stripboard layout

It includes the indicator for the clock out, which has separate ground and +V power supply connections, presumably in an attempt to keep the audio path clear of any clicks from switching the LEDs. On the original (and on mine) this is powered by 22V, but it should work off 15V.

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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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