ba662 tall clown arrives

clown comparison

Having given up trying to hand solder the SOT-363 bits on the OpenMusicLabs BA662 clone/clown, here’s a version with BCM847DS/BCM857DS transistors instead of the dust-like PMP4201/5201.

No idea if it’ll work. The specs look almost identical, apart from a tighter hfe tolerance on the smaller device which I don’t think will matter anyway.


703e VCF with LM13700s

Someone asked on electro-music about subbing a LM13700 for a couple of CA3080s in a Roland-style filter, so I thought I’d have a go. I levered out the 3080s in my 703e clone and wired up three LM13700s (two for the four poles, one-half for the resonance control) and to no-one’s great surprise, it works.

Here is some quick fiddling with an out-of-tune clone 700 oscillator into the 703e VCF.

It sounds a bit overdriven to me – I was trying to avoid any red lights, but being in a hurry to get something down it’s possible I got something wrong along the way.

Now I think about it, it could be that I didn’t recalibrate the DC offset trimmers from when it was set up with the 3080s.

The wires strewn all over the board probably aren’t helping either, so I’m tempted to build up another 703e and make some LM13700-to-CA3080 adaptors to test this further.


System 100 LFO fixing

System 100 102 module VCF/VCA board

While making a godawful racket with the System 100 on Saturday, I switched to PWM on the 102 VCO and the pulse width stayed unmodulated. The LFO light didn’t light, no matter how much I waggled the slider. Hmph.

Should be easy to sort out a broken LFO, right? I’ve built all the bits of a 102 on stripboard, so surely I should be able to fix it?

Fretting that it wouldn’t be as easy as all that, I peered at the schematic.

102 LFO schematic

None of the outputs were working, so I reckoned the problem was in the tri-core, either the capacitor or the op-amp. Just to check, I measured the output of IC301, and it was pinned high.

At this point feeling strangely optimistic, I enlisted the help of my son, who was bored enough to come and watch/help/encourage/take the piss as appropriate. Is dad gonna be able to fix this thing?

I yanked out the CA1458G in IC301 with a desoldering gun:

Dead CA1458

I bunged a socket in, and replaced it with an MC1458 I had in the bits box. So far, so good.

Replacement MC1458 in place

Switched it on, and…

…it worked straight-away. WHOOOP.

I probably should have measured all the voltages and given it a bit of a once-over before I put it all back together, but my son was keen to start making some horrible noises, so I just had time for a couple of slightly wobbly bonus photos: here’s the VCO board – see all the keyboard specific components left unpopulated:

System 100 102 VCO board

and here’s the ring-mod/S&H board

System 100 102 ring mod board

It’s missing the circuit board annotations that my 101 keyboard has, and the soldering on the back is without solder resist (more like earlier System 700s, or my SH-5). The serial number starts with 46, so according to that Boss serial number lookup chart, it was made in May 1976. My 101 keyboard serial is 60xxxx, which works out to be July 1977.

Here’s my Sys101 VCF/VCA for comparison.

System 100 101 keyboard VCF/VCA board

I’ve not gone over the board to see if there are any differences in terms of components; there’s nothing extra soldered on to the back of the 102 VCF/VCA board, which suggests probably not. I pulled out the circuit board for my 104 sequencer recently, and it has a different circuit board layout to the one in the manual, with a load of bodged extra capacitors soldered to the back.

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