Bell Tone Synth Works

How Sound Selection works in the Yamaha CS-80

One of the things that has been the most helpful for me over the years in sort of syncing up my general understanding of electronics theory with understanding how synthesizers are actually designed is reading circuit descriptions in service manuals. A lot of the American companies especially wrote really great, detailed explanations of how their instruments worked, and reading them has helped me to both understand the specific circuits they discussed, and understand more broadly how different objectives in synth design can be achieved… and more quickly recognize what’s going on in an unfamiliar circuit.

Because I’m a nerd I guess, I thought it might be fun to make some step-by-step “circuit descriptions” like that for synth circuits that don’t have them. My first featured circuit –the system through which the Yamaha CS-80 handles preset, panel and memory switching– is sprawling, but actually fairly simple, much like the synth that it comes from. Continue reading “How Sound Selection works in the Yamaha CS-80”

Restoring the Saddest Minimoog in the World

When this Minimoog Model D arrived a couple of years ago, it was probably the absolute most thoroughly wrecked synth I had ever agreed to work on. I made a deal to do it for a flat fee, even though I knew it wouldn’t be technically “profitable,” under the condition that I could take my time on it, kind of as an absurd challenge to myself and because I knew it would be really satisfying when I finally finished it. Since it is finally done and restoring it was such an insane gauntlet of tasks, I thought it might be worth reviving the long-neglected Shop Blog with a post about it! Continue reading “Restoring the Saddest Minimoog in the World”

Double Sequential Circuits Prophet 10 Restoration

While we’re working from home due to the virus and have all of the synths and all our recording gear in the same place, we took the opportunity to make this video about the restoration of two Prophet 10s we’ve restored recently. One of them proved to be one of the most arduous restorations we’ve ever done due to massive damage to its microprocessor system. It was a long road to get it working, but when it was done, we celebrated by MIDI chaining the two of them (which we had also both retrofitted with MIDI) and making some fantastic and massive PROPHET 20 sounds! Check out this video for a recap of the restoration process and some demos of the synths’ powerful sound.

The MemoryMoog (Plus): American Monster Polysynth

The development and release of the Moog MemoryMoog (and MemoryMoog Plus) was the last gasp of the Moog company in the 80s. Around 1980, the two younger American synth companies, Sequential Circuits and Oberheim, were thriving, putting out one new synth after another. By the time the Memorymoog came out, SCI and Oberheim had already released multiple true polysynths. The Japanese companies were cranking out one new polysynth after another. The two remaining from the old guard of major American synth companies, ARP and Moog, were acutely aware of the serious market pressure to put out polysynths of their own. Each had already barfed out a big, cumbersome, paraphonic psuedo-poly (the ARP Quadra and the Polymoog, respectively) but it was REALLY time for them to get their act together, hire some programmers and design a true polysynth with digital voice assignment and control.

Continue reading “The MemoryMoog (Plus): American Monster Polysynth”

EML 101 and 100 1 V/Octave Mod PCBs and Kits now available

EML-101/100 1 V/Octave Mod kit installed

PCBs and kits are now available for the circuit we use to add 1V/Octave scaled input to the ElectroComp EML-100 and EML-101 synthesizers!

The EMLs use between 1.2 V/Octave and 1.4 V/Octave (varying from one unit to another) with an offset of between 4.2V and 4.6V. Our board allows you to feed in conventional one volt per octave control voltage from another synth, controller keyboard, sequencer, etc. and scales it up so that the EML’s second-voice oscillators (Oscillators 3 and 4) can track it. Using a sequencer especially opens up amazing possibilities for this already very powerful synth!

Our original version of this circuit just performed the summing and amplification and required the installation of a new external switch to turn the mod on and off. Our new version uses a multiplexer to automatically perform this switching task when a plug is inserted in the CV input jack. This means that it can be completely invisible– no hole needs to be drilled, and the synth functions 100% as original when nothing is plugged in.

The mod can be used on both versions of the EML-101. On the later version that has a “Sequencer” jack, the Sequencer jack becomes the 1V/Octave input, and on the earlier version, another jack can be selected to be the new 1V/Octave input (we use CM3).

The PCB will come with schematics, bill of materials and detailed installation and tuning instructions with lots of full-color photos. The kit will come with all of the above plus all required parts and the jack already partially wired (because this is probably the thing people are most likely to mess up!)

The PCB and kit can be ordered here!

Vox Jaguar with Missing Filter/Switch PCB

Heathkit Vox Jaguar

I don’t usually post about combo organ repairs because I don’t think they’re very interesting, but this was one of the weirdest ones we’ve ever done! The owner of this Vox Jaguar organ told us that he had had it for about 10 years and it had never made sound at all, which didn’t really faze us because that is a common complaint for a piece of equipment this old. But when he dropped it off, we opened it up and discovered the reason that it wasn’t making sound was far more serious, and far more crazy, than we had expected. The tone filter and selection board, including the switch contacts, was missing ENTIRELY. The rocker switches were all present, but connected to nothing. The signals from the oscillator/divider boards were simply not being sent anywhere at all. Continue reading “Vox Jaguar with Missing Filter/Switch PCB”

“Don’t be that guy”

Roland CSQ-600: in which the tech replaced the NiCad memory battery but installed the replacement battery in a ziploc bag ziptied to the mains wiring.

One interesting thing about restoring vintage synths is that almost every instrument that we work on has been worked on by another tech at least once before. And it seems that more often than not, those other techs were… not great. We see a lot of bad work, but my favorite examples also feature a very special element of absurdity. Here are some recent highlights:

ARP 2600

The owner of this ARP 2600 got it in an insane trade in the late 80s… in exchange for a Peavey keyboard amp and a TR-505! A lot of it had never worked in the entire 30 years he had had it.

When we do restoration of an ARP that’s in bad shape, we’ve learned that there’s really only one good way to approach it. We basically strip it down to its bones and do everything we possibly can in one fell swoop before even trying to test different systems. It ends up being so much more efficient that it actually costs less than taking a more step-by-step approach.

Rebuilding ARP PPCs

Using FSRs (force sensing resistors) to repair PPC "proportional pitch control" pads for an ARP Odyssey Mark III

Because I am now one of those people who thinks they are very busy, I am just going to share a “quick tip” today.

In one of several Odysseys that we rebuilt recently, the “Proportional Pitch Control” pads (otherwise known as PPC, those three spongy white pads that Mark III Odysseys have) were so bad that no amount of cleaning could revive them. I finally was forced to look for another solution, and tried using some FSRs (force sensing resistors) and the results were great.

Now Available – Precision Cut Slider Gaskets / Dust Protectors for Juno 106, SH-101, Juno 60, Jupiter 8 and more!

Roland Juno 106 slider gasket / dust protectors set

One thing we find in almost every 1980s Roland we work on is crumbly, dirty “dust shields” or “dust protectors” on the sliders (aka faders) of the panel board. These gaskets were cut from thin black EVA foam sheets and were meant to protect the sliders from dust. However, 35 years later, they have dried out and are falling apart, their fragments actually falling into the sliders and making their crackly and intermittent behavior much worse.

Bell Tone Synth Works now offers laser-cut replacement gasket sets for the Roland Juno 106, SH-101, Juno 60 and Juno 6, Jupiter 8, and CompuRhythm CR-78, which you can purchase online here in our Shop. These slider gaskets are made to exact specifications on a professional laser cutter out of 1.5mm stiffened and resin-bonded black acrylic felt which does not shed fibers like other forms of felt. Continue reading “Now Available – Precision Cut Slider Gaskets / Dust Protectors for Juno 106, SH-101, Juno 60, Jupiter 8 and more!”