Sheriff JW brought his Akai X7000 boat-anchor/sampler round for a bit of attention. He’d replaced the long dead 2.8″ QuickDisk drive, and that bit worked nicely, but he said that the output had gone really, really quiet.

He wasn’t kidding – It was so quiet, we couldn’t hear anything out of the line out at all, and only some very faint sounds out of the headphone output.

Before getting my hands on it I thought that there was a possibility that the main output opamp was dead, but after having a poke around on the voice board, I found that couldn’t measure much of any sort of a signal, with only the headphone output having anything measurable at about 10mV.

The user interface itself worked happily, I could navigate around, select programs, twiddle the values for things like the filter, and load samples from the QuickDisk replacement drive. But it was just really hard to hear anything.

Finally I realised that I should just check the power rails, because that’s what you should always do first (…yeah), and the +V on IC4 on the output was 3.8V or thereabouts. The -V was less than a volt.

The service manual says that the voice board gets +/-15V and +/-5V, so this seemed badly wrong. I disconnected the cable to the voice board, and measured the voltages on the PSU board directly, and got 0V.

…and then, only then – I noticed the fuses.

I didn’t take a photo of the insides (this is rare for me, I love this sort of thing) but they’re really obvious on the PSU board at the bottom right, just a couple of T500mA glass fuses. And they measured open.

I replaced those and ta-daaa, finally we got samples played at full volume in glorious 12-bit.

The samples from the Akai sound library that were included with the solid state QD-replacement drive were pretty nice (if you like that sort of thing), lots of nicely looped stuff. Shame there couldn’t have been an easier way to have the disk drive screen on the top, as it’s otherwise pretty convenient to use this for selecting presets.

Anyway I managed to get a chopped up “Hot Pants” loop going round, then sampled a bit of Whitney’s “So Emotional” as is traditional, but then it had to go back with its owner.

“Hot Pants” just seems to sound really nicely rough in that aggressive sort of way in the X7000 when sampled at slightly too low a bandwidth, it has such a nice hard texture to it. None of my DIY drum loops ever quite come through in that same rough way.

All my samplers are just rack units, but actually having one with such a wide keyboard built-in is quite nice, makes it very immediate. But it’s too big, and I’ve long since ran out of room.

Anyone with any sense would just buy Tubbutec’s apparently excellent Juno-66 mod and be happy, but just for the freaks I’ve finally fixed my Juno-6 DCB interface layout so it’s now ready for sharing.

Here are the Gerbers, zipped up ready for the likes of JLCPCB:

juno-6-dcb-rev-b.zip

…and here’s the BOM.

Basically it’s this bit of the Juno-60 schematic broken out into a separate board.

Now it’s the 21st century all this could probably be replaced with some sort of microcontroller rather than having to go through all this faff, but here we are anyway. And this keeps it authentically 1982, if that matters to anyone.

Here’s the layout, featuring my usual drunken wobbly routing:

Note the annoying mixed orientation of the ICs (U1 and U4 pointing downwards, U2 and U2 upwards), yeah, I know.

The connectors on the left are all labelled and they’re in the right order to connect to the pins on the right of the Juno’s main board, which are also all labelled up. DB1 is just labelled “1”, as I wasn’t able to squeeze the rest of the letters into that bit of the PCB.

It’s powered off 5V, and there’s a header on the Juno main board for the gate outputs which includes a ground and 5V line, which is where I ended up taking the power for this board.

Just for completeness, here’s my schematic as a screenshot (and here’s the strangely massive PDF):

Given all that and you’re daft enough to still want to give a go, when I bought my boards from JLCPCB in early April, they came out as £4.89 (including postage to the UK, as an example) for 5 boards on the cheapest settings.

This is probably one of those mini-projects where you have to be very confident about opening up synths and messing around. Juno-6s are now worth a fair amount, and I’d hate anyone to kill theirs as a result of trying this board out.

I would really recommend testing the PCB outside of the Juno first; check to make sure 5V and ground aren’t shorted, and power it up from an external test power supply, and check that the outputs aren’t putting out strange voltage levels.

The original connectors were Amphenol DDK types, and are obsolete as far as I can tell. As I don’t have any original Roland DCB gear to play with (and my urge to buy an MSQ-700 has faded now the prices have gone crazy), I used a DIN connector, which is a special kind of pain in itself – I’ve never liked wiring them up.

Eventually I’ll get round to writing up the CV/gate/MIDI to DCB box as well, here’s the mildly shoddy (but practical!) box for that:

A few months back the octave switch on the first oscillator of my Irish theme pub synth, the Sequential Circuits Pro-One, started to miss out certain octaves when switching. It’s the switch with a black base and and manky off-white stalk towards the top in this photo:

I had a look at the schematic and hoped it might be a dead logic IC or something, as I wasn’t sure if the switch would be available forty years later. Also, what kind of switch is this?

I poked around with my multimeter, and boo, it was the switch. It wasn’t making the connection on particular footage settings.

I had a search around and it turns out it’s a double pole, four position rotary slide switch, and according to the excellent A to Synth blog, it’s actually still available in the form of the C&K R20407RN02Q from Farnell or Mouser for about £6 or so.

Although I say that now, I didn’t find out it was still generally available until after I’d ordered a replacement on eBay from a seller in Spain for twenty quid. Curses – but a grudging hats off to the guy in Spain for marketing his listing well, I guess.

I wanted to desolder the original switch cleanly in case I could take it to bits and fix it but it…disassembled itself.

Whups. This was due to a bit of mild violence when trying to get it off the board. At least we can get an idea of how it works – those silver discs slide into cutout sections either side of the base of the shaft, and connect adjacent pins.

It looks almost as if I should be able to rebuild it, but I think I’ve trashed the tiny plastic clips that hold the black top of the switch in.

It took me far too long to get it off the board, despite my desoldering tool.  More as a reminder to myself; the tactics should be:

• add some fresh solder to the pin
• press the tool over the pin
• wait until it obviously melts
• press the button, waggle the tool over the pin,  and suck all the solder out for longer than you think
• check that the pin is no longer attached to the hole, but pushing the pin the edge of a screwdriver or something to see if the pin moves, and therefore is no longer attached to the edge of the hole
• add some fresh solder if it’s still attached, and try desoldering again
• once you’ve finished, clean all the old solder out of the solder sucker

Here are the desoldered holes:

And here’s the newly soldered switch – being careful to align pin 1 on the switch with pin 1 on the board:

And it works.

I mean I am glad, it’s just kind of a bit boring.

Time to put it back together. Thanks for checking it over Wendy:

To finish off I gave it a bit of a clean-up, and reglued some of the previously-Araldited panel standoffs that had broken, and now it works nicely and looks good again, despite the lack of side panels. I could get some replacements but it wouldn’t fit in the space next to my MC-4, so it stays like this for now.