ba662 tall clown

pile of clowns

Here are the Gerber files for my version of the Open Music Labs BA662 replica.

I’ve called it the tall clown ‘cos it uses BCM847DS and BCM857DS dual transistors, rather than the tiny PMP4201/5201 in the OML version. It’s a bit easier to hand-solder than the OML original, but not much.

I’ve tested these in my System 100M clone and they seem to work, but ymmv.

The filenames follow the iTead naming convention, and the board size is 22.0 x 12.1 mm.

If you prefer, here’s a link to the (untested) project on Oshpark – three boards will cost $2.05.

clown full frontal

Thanks to Open Music Labs for doing all the hard work on reverse engineering the circuit. This particular layout is my fault, so blame me for that.

Here’s a handy map of where things go – it’s from rev A, but the components haven’t changed position. The resistors are both 0805 sized.

ba662 tall clown map

If you can’t be arsed with soldering such tiny components, the OML versions are distributed through Synthcube, try them instead.

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Flashing lights of the 100M

Continuing with some stuff from my ongoing silly giant-sized clone 100M – here is the flashing lights bit from the VCA and VCF circuits in action.

It’s unlikely it’ll be of any use to anyone, ‘cos it uses a (possibly unregulated) 22V power line from the 100M PSU, but, just in case – here’s the layout:

Roland System 100M level indicator stripboard

The lights on the 100M are meant to be useful, telling you when signal is coming out of the output, and if you’re pushing the level too hard. In practice, the overdriving seems to kick in slightly before the red light comes on.

It’s lot of effort for some pretty lights, but the whole thing has been a ridiculous endeavour so far anyway; so in for a penny, in for a pound.

The 100M level detector works more reliably than I’ve so far managed with the System 700 equivalent, which seemed to need very specific transistors, and even then occasionally gets stuck.


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.

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