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.

No Comments

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.).

1 Comment

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 the 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.

1 Comment