Digisound 80 refurbishment

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bennelong.bicyclist
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Digisound 80 refurbishment

Post by bennelong.bicyclist » Tue Jul 16, 2013 5:17 pm

In this thread I'll document the refurbishment of the Digisound 80 modular that I built in about 1982 from kits by Charles Blakeley's Digisound company in Blackpool, UK (um, the kits were built in Sydney, Australia, which is where the synth and I still live).

I built the thing, but then became busy with other things, and it has been stored in various (often damp) sheds, garages and lofts for over thirty years. Time to rehabilitate it.

The modules are all housed in a custom self-made case made from L and T section alumunium beams and aluminium sheets (both easy to cut and drill), just bolted together. The panels were covered with self-adhesive blue kitchen drawer vinyl.

It has 22 modules: 4 x VCO, 1 x VCLFO, 1 x Dual Resonant Filter, 1 x State Variable VCF, 2 x lowpass VCF, 2 x dual VCA, 1 x VC mixer, 1 x dual Ring Mod, 1 x Noise/S&H, 2 x VCEG, 1 x dual EG, 3 x voltage processors, 1 x external input/envelope follower, and 1 x BBD analogue reverb.

Here it is after I removed a few of the modules (and with back panel of case removed):

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Post by bennelong.bicyclist » Tue Jul 16, 2013 5:29 pm

A few of the modules. Yes, the one at the top left has the PCB mounted on the panel the wrong way around - it was the first one I built... but after it was wired, there was no way I was going to redo it. No functional deficit.

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Close-up of my slightly idiosyncratic wiring style.

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Post by bennelong.bicyclist » Tue Jul 16, 2013 5:34 pm

The weird white crystals growing on some of the trimpots (but on nothing else) (previously posted). Seems like it hasn't affected them (but I have yet to re-calibrate any of the modules).

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More modules removed from the case:

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Post by bennelong.bicyclist » Tue Jul 16, 2013 5:44 pm

View from the rear of the case:

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The power supply (+/15v at 1A). Heatsink for power transistors bolted to the aluminium case frame, ventilation hole covered with flyscreen mesh beneath transformer:

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In retrospect, the safety of the mains wiring left a lot to be desired (don't worry, I will be attending to that as part of the restoration):

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Hmmm... And yes, that is a dead gumtree leave at the bottom of the case - needs a good clean and vacuum:

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Post by bennelong.bicyclist » Tue Jul 16, 2013 6:21 pm

The very nice Blacet PSU which will replace the Digisound PSU (one rail of which is dead, and too much trouble to fix it):

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The original power distribution bus:

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Detail of the original power distribution bus:

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dougt
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Post by dougt » Wed Jul 17, 2013 1:03 am

Cool! Good luck with it. I also have a Digisound I've mostly restored...

I got this system about 12 years ago (plus a box with some extra modules and parts) -

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I wonder how many others on here have these... I've actually never seen another one in the US...

Have you found a source for the Chiri power connectors?

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Post by construct09 » Wed Jul 17, 2013 3:20 am

Thanks for this thread :tu:

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Post by Morley » Wed Jul 17, 2013 5:45 am

Nice
I had a system for a while. Always liked the design.

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bennelong.bicyclist
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Post by bennelong.bicyclist » Wed Jul 17, 2013 5:00 pm

dougt wrote:Cool! Good luck with it. I also have a Digisound I've mostly restored...

I got this system about 12 years ago (plus a box with some extra modules and parts) -

I wonder how many others on here have these... I've actually never seen another one in the US...

Have you found a source for the Chiri power connectors?
Oooh, nice system! A google search reveals one or two ancient web pages with details of systems that look like they are, or were in the US. Not common here in Oz either. I suspect that there are quite a few squirrelled away in lofts in the UK.

I have just enough Chiri connectors for the modules I have - I just hope none of them break. I spent several hours googling for more - no luck. If they do break, I'll have to just solder the power leads to the PCB, which is OK for (bedroom) studio use (my dreams of live gigging have faded...).

BTW I received the CEM VCO and CA3080 chips you sent, many thanks. I want to complete the PSU work first before trying them. I may need one or two CEM dual VCA chips for the VC mixer modules, pending further testing.

If your additional Digisound modules are ever surplus to requirements, let me know - I still have two spots left in my case.

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Post by bennelong.bicyclist » Wed Jul 17, 2013 5:05 pm

Morley wrote:Nice
I had a system for a while. Always liked the design.
Any photos of it you could dig up?

No, on second thoughts, don't bother. Collecting vintage Blackpool synth modules is one thing, collecting photos of them is quite another, and a step too far.

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Post by Morley » Wed Jul 17, 2013 5:10 pm

bennelong.bicyclist wrote:
Morley wrote:Nice
I had a system for a while. Always liked the design.
Any photos of it you could dig up?

No, on second thoughts, don't bother. Collecting vintage Blackpool synth modules is one thing, collecting photos of them is quite another, and a step too far.
:hihi:
Not sure I do but will look anyway. The (custom) front panels were green!

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Post by bennelong.bicyclist » Sat Aug 10, 2013 3:58 am

A bit more progress: the Blacet power supply has been installed, the mains wiring replaced and made safe (but I'll still use a RCD on the mains line), new power distribution wiring loom, and now all 4 VCOs are operational, thanks to two new CEM 3340 chips from Doug at synthparts.com. One of the VCO modules was very wibbly-wobbly at first, but replacing the CA3080 OTA chips fixed that too. Now all four are completely stable, and sound great (the soft sync on the Curtis chips is still awesome).

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Next step: calibrate all four VCOs (and the LFO, also CEM 3340-based, same PCB as the VCOs).[/img]

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Post by Dcramer » Mon Aug 12, 2013 10:35 am

Amazing system! I can't believe the patience and skill you DIY's have! :party:

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Post by krisp14u » Mon Aug 12, 2013 11:59 am

I overhauled my Digisound last year replacing every pot and jack socket with the intention to sell it on
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Its now my pride and joy and I hope I never have to sell her

good luck on the restoration keep posting pics

dougt wrote: Have you found a source for the Chiri power connectors?
http://www.rapidonline.com/Cables-Conne ... ors-200054
Cheers :guinness:

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Post by bennelong.bicyclist » Sat Aug 17, 2013 12:07 am

krisp14u wrote:I overhauled my Digisound last year replacing every pot and jack socket with the intention to sell it on

Its now my pride and joy and I hope I never have to sell her

good luck on the restoration keep posting pics
Awesome! I wouldn't sell that, either. My sons keep asking me "How much is it worth?" and "Are you going to sell it?" My answers: "Priceless, because I built it myself when I was only a few years older than you." and "Never."

That said, I've stopped pining after any more Digisound modules to complete my cabinet (I've got two spare spaces). What I really need is an affordable DIY multi-channel MIDI-to-CV controller. I was going to go down the Expert Sleepers route, on the assumption that the tuning and stability of the VCOs would be all over the place, but since replacing the power supply with the Blacet PS505, and replacing all the OTAs and op amps (and two fresh CEM chips), all four seem rock solid and are keeping their tune perfectly, once it warms up for 10 minutes. And besides, I have soldering iron fever again.

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Post by bennelong.bicyclist » Sat Aug 17, 2013 12:10 am

krisp14u wrote:
dougt wrote: Have you found a source for the Chiri power connectors?
http://www.rapidonline.com/Cables-Conne ... ors-200054
Yup, those are the CHIRI connectors specified for the Digisound. I should order a few dozen as spares. Thanks! Doug T at SynthParts, please note.

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Post by bennelong.bicyclist » Sat Sep 07, 2013 2:00 pm

A Digisound 80 module! A VCDO in fact.

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Post by construct09 » Sat Sep 07, 2013 11:32 pm

...and a Joy Division synth :hail:

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Update on refurbishment

Post by bennelong.bicyclist » Mon Sep 30, 2013 5:42 pm

Proceeding slowly. Borrowed an old analogue oscilloscope from a friend to assist with the calibration - not re-calibration because I never got around to calibrating it 30-odd years ago after I built it. So far, so good. Oscilloscope essential for adjusting the sine wave shape and p-p voltage of the VCOs. Found two of the multi-turn cermet trimpots were dead - replaced those. Using an iPhone app called n-Track to measure frequency (just through a speaker and the phone microphone). Reference voltage for tracking/tuning from a Doepfer Dark Link USB/Midi-to-CV convertor. It only uses an 8-bit DAC but seems fairly accurate. Wrote a Python script to emit MIDI to the Dark Link to step through octaves while I tweak the trimpots on each VCO. So far I seem to be able to achieve +/- 2 cents tracking accuracy on each VCO over 5 octaves (which is the range of the Dark Link) - which seems pretty good to me, given that the minimally- detectable difference in pitch is supposed to be 6 cents. Pitch starts off about 10 cents off until the VCOs warm up, but the tracking seems stable. Is that sort of tracking accuracy good enough? Of course, the residual inaccuracies may lie in the Dark Link. I'm hoping to acquire a Kenton MIDI-to-CV convertor, which uses a 16-bit DAC and should be far more accurate. Lots of fun demonstrating waveforms etc on the scope to my 11 yr old.

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Post by leeski » Sun Oct 20, 2013 12:44 pm

Wow this is rather good read, :tu: :yay:

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Post by bennelong.bicyclist » Fri Oct 25, 2013 10:25 pm

More progress! I was fretting because the VC Mixer module wasn't working, due to two dead CEM3330 dual VCA chips (the modules uses 3 of them). Doug at synthparts.com (highly recommended purveyor of CEM and other hard-to-get synth chips and parts) didn't have any in stock (at least, not when I enquired - he subsequently got hold of some, I think). But I managed to track down three used CEM3330s at reasonable prices by scouring eBay for expired auctions of CEM chips and then emailing the vendor asking if they had any more. Found two CEM3330s in the Netherlands and one in Germany, which I bought directly (not via an eBay auction). They duly arrived here in Oz. The two chips from the Netherlands looked a bit worse for wear and had several bent legs, but after some judicious bending they slotted into the sockets OK, The chip from Germany was pristine. And, somewhat to my surprise, they all worked! So now I have a fully functional Digisound 80-4 VC Mixer module, and a spare working CEM3330. In fact, now all 22 of the modules which I built 30-odd years ago are working again, and all are fully calibrated. Next step is to replace a few dodgy jack sockets and about a dozen panel pots that are just too scratchy to tolerate. Refurbishment should be complete by Xmas. I have asked Santa for some new patch cables...

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Post by snufkin » Sat Oct 26, 2013 10:46 am

I think you should try and track down some nos kits to fill the gaps >:)
WTB: any Digisound80 / Digisound 80 faceplates/pcbs/kits.

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Post by NYMo » Sat Oct 26, 2013 12:53 pm

Nice work...hopefully it will last for another 30 years :hihi:

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Post by fireclown » Sat Oct 26, 2013 2:23 pm

what is the architecture of the dual resonant vcf?
Pair of 3320's?
just curious.
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Post by Morley » Sat Oct 26, 2013 3:19 pm

Some lovely systems guys!
Krisp1 Yours has a great balance of modules.
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