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Musical Technology

Yamaha DX7S repair notes

Posted under Musical Technology at .
Tags:DX7S, hardware, instrument, repair, synthesiser, Yamaha

Shall I say that DX7s need no introduction? Well there are more web pages than I’d try to count about them, so if you need an introduction, go get it.

The original DX7 to me was that sleek thing with membrane keys which, in 1984, someone I knew got hold of, praised the capabilities of effusively, and left me with unattended for a few minutes. Being sort of used to simple analogue synths, I thought, well, let’s see? And pressed a few membranes, managing to change what it was doing out of all recognition in a few short seconds, with no idea how to change it back. Up DX7 creek without a manual, nor any clue how I got there. I thought it would be best to just leave it rather than make things worse. Leave it at speed, before its owner returned. I never saw it again.

Clearly this memory has stayed with me. In fact it’s probably the exact reason why I prefer proper synthesisers, i.e. ones with a control for each parameter, that you can see, adjust, and then put back where you found it. Nevertheless, I’ve always thought that one day I would like to find out how to use the thing. One of my own, without the risk of wrecking someone else’s setup again.

So, here we have one of the DX7 updates, a DX7S, from 1987 I think, and in need of some attention. I’m not sure what’s wrong with it, but battery replacement is apparently wanted. Hopefully not much more than that.

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A Spotter’s Guide to HIPs and Strings

Posted under Musical Technology at . Last updated 2022-05-05 17:11.
Tags:artwork, ELEX, ELKA, Hohner, Logan, piano, reference, string machine

A summary of investigations into Hohner analogue electronic pianos and string machines. (To date. Not planning any updates at this point, but you never know.)

Not long after the technology became reasonably affordable, Matth. Hohner AG sold several electronic piano and string machine models under their Hohner International brand, apparently aiming at cheapness and portability compared with their acoustic and electromechanical keyboards. Most of these were either rebadged ELEX (Excelsior) products or perhaps Hohner-inspired modifications of them. Some were rebadged ELKA and Logan instruments, and they produced a couple of their own designs. [1] (Hohner did also produce organs, bass keyboards and pedalboards, acoustic and electromechanical piano-like instruments amongst others, but that’s not today’s topic.)

The plethora of these instruments from different manufacturers, some sold as Hohner, some not, some easily distinguished, some not, some modified either inside or out over their production span, has led to a certain amount of confusion in the years since, and poses a puzzle for people interested in obtaining and/or repairing them. But perhaps it’s possible to construct a comprehensive overview which will allow them to be identified and distinguished?


HIPs and Strings

Ephemeral photos of most of these instruments turn up occasionally in online sales; longer-term linkable references are given below. Different branding seems to have been used by Hohner in different national markets, however, so even if this list is comprehensive technically (which I can’t guarantee), there may be alternative names in some parts.

Drawings below are sketches intended to highlight the distinguishing characteristics of the instruments, rather than be exhaustively accurate. Or get the perspective right or anything. Slider caps in particular may vary even in the same model; so I’m not trying too hard to represent the exact types found — where they haven’t all vanished or been replaced.

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Korg SD pictures

Posted under Musical Technology at .
Tags:BBD, Korg, musical equipment, photographs, SD‑200, SD‑400

Side by side shots of the Korg SD delays, the -200 opened for comparison while I convert the -400 for 240V.

Korg SD-400 and SD-200 front panels

The SD-400 (brown) has the bypass, short/long delay option, swell, and ADT settings, but no tone control. I haven’t quite worked out which I prefer; the -400 seems to have a fixed filter; it’s smoother than the SD-200 (silver) on simple delays, unless you turn the -200 tone down. Maybe the -200 is better for harsher delays. The only online technical information I’ve found for them suggests they have roughly the same range of 30–400ms for the -200 and 25–400ms for the -400. Presumably the -400 should go lower on its Short setting, but it’s the same as the -200 on its Long setting. In practice, comparing these two, the -400 gets up to around 10% longer delay, but that could just be a calibration thing on one of them.

Korg SD 200 and 400 open

Vermona Synth Question

Posted under Musical Technology at .
Tags:hardware, instrument, KHW, questions & answers, synthesiser, Vermona, Synthesizer

Message Received

Flavio, 2016-06-06

Hi there!

Thanks for your articles on the Vermona Synthesizer - I read entirely through the first part, went a bit too techy in the second article but still very interesting.

I got my Vermona Synthesizer a couple of days ago and I’m now facing two issue, which I hope you can help/suggest how to solve them.

First of all: for VCO 2 the register buttons don’t remain pressed (none of them). I opened up the synth and I found out that the mechanism is somehow stuck in the open position (the position in which nothing gets blocked).


Second issue is the keyboard: as some keys were having double triggers or didn’t trigger immediately, I took an eraser and tried to clean up what was accessible without removing any keys at all. I also moved the plated bars slightly a bit more left and then back right . . . now I got the lower 4-5 keys which play the same note (???) and all the others play ok but some of them are still not clean enough. What is your suggestion for this issue?

Thanks in advance and kind regards,



Well, sometimes I am a bit too techy. Until it’s the too techy bit you want. Ignore the rest and let the search engines read it. (happy emoticon)

(I’m writing these articles because I find it useful to record all the information I discover — less or more techy; and the interesting or entertaining thoughts that happen while looking; I’m publishing them specifically because I usually can’t find the exact techy bit I want online, or anywhere else . . . )


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Vermona Synth Boards

Posted under Musical Technology at . Last updated 2019-09-10 00:00.
Tags:artwork, hardware, instrument, KHW, synthesiser, Vermona, Synthesizer

In spite of the apparent quietness of the last few months, I’ve been working on synths in between other things; in particular on the Vermona. After the initial post, in the absence of any written technical information, I was planning to draw my own circuit diagrams. Actually I did some board drawings, because that’s easier when all you have are last year’s photos and enough space to sit. (happy emoticon)[1] A couple of weeks ago, this was complicated by my discovery of a new (I think) and rather great old manuals page at, which includes circuit schematics [2] for both versions of the Synth. The full update I was slowly working on will be rewritten in the light of the new information . . . but it will be better. For now, here are my drawings — with the component numbering brought into line with the schematics, as far as possible. (My earlier numbering was entirely arbitrary as there is no screening on the boards.)

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Korg MS-10 Notes

Posted under Musical Technology at . Last updated 2022-06-02 06:39.
Tags:instrument, Korg, MS-10, synthesiser

MS-10s need no introduction, so — here’s one. Probably from about 1980 but I haven’t got it far enough apart to look for component dates.

front (on arrival)

This arrived in a purportedly Pro-Serviced state. In contrast to my many other gripes on the topic, I must note that it was well-packed, and arrived faster than the estimated earliest date. Also in near-perfect physical condition, which for me is a first, for a synth without a case. So would buy again? Maybe. It doesn’t even smell bad. No rotting food or wildlife, no decaying components, no decades of garage-storage and no undead tobacco. [1]

But I’d like to know what Pro-Serviced means. Perhaps that this time I’m paying someone to do the things I would normally do myself? This clearly doesn’t include cleaning, past a cursory wipe; there’s a lot of dust ingrained on the modwheel and at the back of the keys.

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