blueshift dim-c clone

Done done done. I made the holes for the switches a bit too big, might need some bigger washers.

Aion Blueshift boxed

Really boring round the back, it’s pretty tight.

Aion Blueshift inside back

Inside! it’s packed out. If I’d’ve designed this board it would’ve ended up about two feet square.

Aion Blueshift inside

If you’re going to build it, use the specified capacitors – the ones I used were too tall, although I’ve just about got away with it.

I’ve recorded some basic demos just to get an idea of what the Blueshift does to a source.

Here’s the Blueshift on DC power (hence the hum, unfortunately) having a simple polyphonic JX3P sequence shoved through it while I flip the switches at random. See if you can tell when I turn the Blueshift on:

And here’s another one on battery power, first section no effect:

It seems like it’s very shy of higher levels – I had to notch the JX3P down to its “M” output level to avoid distortion, and like I say, it seems to hum with the DC adaptors I’ve got, although I don’t necessarily trust any of them.

But I really like the way it sounds, and it can do exactly what I wanted, which is to widen a mono source without sounding too obviously swooshy and chorused.

The pedal format isn’t really ideal in my studio but I just wanted to get it done. I’ll pretend now that I could make it into a half-rack or something, but that won’t ever happen.

It’s so nice I’m tempted to have a look at making a more rack/studio-ish Dimension-D-type thing, maybe J├╝rgen Haible’s Subtle Chorus or something. But this will do for now.

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LED indicator noise in System 700

I’ve never been able to get the LED indicators to work well in any of the System 700 circuits I’d made. Even with no input, the green light would stay on and horrific screechy noise would get injected into the output.

Vowing to finally get it sorted out I connected up my 703E VCF clone, got the expected horrible noise and stuck my oscilloscope on the +14.4V LED power line. It showed that the power line was oscillating at about 32MHz, at an amplitude of about 200mV.

Then I tried some stuff like bunging different capacitors on the LED power line and different power supplies, but nothing did the trick.

Some of the schematics suggest that CD4001AE is the right version of the IC to use, although confusingly, not all of them. Also all the pictures of the boards I’d seen have AE or UBE versions of the 4001 in place. Found some old RCA AE variant chips on eBay and gave them a go:

CD4001AE in the 703E filter

DAMMIT IT WORKS.

I wasn’t keen on relying on 35+ year old CMOS chips, so I ordered a few 4001UBE, and they work too.

Mystery solved, put the kettle on.

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JX3P keyboard fixing

After a quick attempt to fix my Midiverb II again (and failing) I pulled the JX3P out again to have an attempt at fixing the dodgy octave.

Thinking that it was possibly the keyboard decoder, I replaced IC45, which took a fair amount of time to do it cleanly with the desoldering vacuum.

JX3P - removing IC45

While I’ve got the board out…

Crinkly JX3P circuit board

not sure I really like the look of these crinkly paths on the back. Anyway onwards.

Changing IC45 made zero difference, so it wasn’t that. And anyway, I could see the signal appearing on the connector on the keyboard. It took me a while to work out what was going on, and it definitely made it easier yanking the keys out.

JX3P keyboard diodes

This is part of the dodgy section of the keyboard, and it looks a lot like my unhappy Poly61M from the same time. The rubbery circular things are pressed down by the keys – inside the dome is a carbon disc that presses down onto the board and completes the circuit.

One side of the switch connects to the top of the diode below it, with the other half connecting to the decoder IC45 via the keyboard connector at the far side. Pressing the switch should make the signal from IC45 appear on the other side of the switch (the top of the diode).

I can’t believe you’ve got this far, but aaaaanyway, the signal wasn’t coming up on the diodes for the broken section.

The soldered track on the far right here should have given the game away

JX3P keyboard connector and track fix

…essentially the track had failed for some reason. Scratching out the soldermask from either side of the break and soldering a wire across it sorted it. It wasn’t actually super-obvious where the break was from just looking at the track, it took me a couple of test scratches to work it out.

There was also one intermittent key which just needed the rubber switches refitting, and that was sorted too.

I still have lots of screws missing (in the JX, that is…), and the transformer hums like an electricity substation, but at least it all works now.

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