I had a couple of guitar pedal PCBs for Christmas, and I’ve had a good time building them up.

This one is my attempt at Jed’s Peds Leadbanger – which is a take on the Boss HM-2. I know that the enclosure is the wrong colour as a match for the original, but it’s really lovely anyway.

I didn’t have a 2N5457 to hand, so I plonked in a BF245A. Also I didn’t have a 250KC pot for the distortion knob, so I just used a linear version, which probably doesn’t help the range of the pot, as it goes from not-much-distortion to angle-grinder-robot-massacre in the tiniest tweak. Reading around, t seems like this is a general problem for the HM-2.

Here’s a bit of typical squeezy funk from my TT-303 – dry at the start, and then you can tell when I flip the switch:

…which sounds pretty good. It’s powered off a 9V battery in these examples, because the random old unregulated Korg Electribe power supplies I’ve got hanging around make it hum like an electricity pylon.

I haven’t quite yet worn my TR-606 out – although you might disagree – here’s a bit of it shoved through the Leadbanger, tweaking things here and there.

When the treble pot get to the end of its travel it gets rather too pinched. It’d be handy to be able to sweep the frequencies of the treble and bass settings, but then that would make it all rather more complicated.

Also for a guitar pedal it puts out loads of bass – some of the other pedals I’ve had haven’t been so good in that regard.

I have to say I really enjoying building it, even as badly as I’ve done with the wonky pots and haphazard enclosure drilling. After having started and not finished so many long-winded, daft synthesiser projects, it’s a treat to build something as self-contained as a pedal.

Also it just feels really good in the hand, sort of satisfyingly chunky. And it’s bright yellow!

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: