After a couple of decades of stagnation, analog DIY synth making is showing a lot of life again. A lot of the classic cicruit designs are no longer encumbered by patents, and many designers who have moved out from commercial production are happy that their designs still attract interest and fans. The late baby-boomers who grew up with synth envy as teenagers are now at the ripe hobbyist age. I guess there is an element, too, of coming full circle: there are great VSTs (many free) for virtual synthesizers and samplers on PCs and Macs, and programs such as Audio Mulch and SynthEdit to let us make all sorts of synthesizers, but these make us appreciate analog sound even more.
But the biggest reason for the resurgence is the strength of open-source: a lot of skilled and mad hobbyists have spent a lot of time passing around designs, schematics, PCBs, improving them and republishing on the web. It is not uncommon to be able to trace a circuit from, say, an Electronotes article in the 60s or 70s through hobbyist improvers or kit suppliers and then through successive improvements by people using the PCBs or kits; eight or more iterations of designs is common. One result of all this is that while in the past the hobbyist designs were often dodgy, nowadays there are far more excellent designs and more variation what is available: in VCFs for example there are multiple versions of the Moog ladder filter in diode and transistor variants, Korg, Steiner Synthacon, EMS, Oberheim, even some attempts at Yamaha and Arp filters. Indeed, many commercial manufacturers of modular synthesizer modules are taking advantage of the open source designs and offer their own versions of circuits that get a good buzz.
I've been looking at suppliers of kits and PCBs recently. For about 25 years, I've had an 80% finished ETI 4600 in storage on my parent's farm. I never finished it because the house I was staying in at the time had previously been occupied by punks (this was the late 70s, when punks were dangerous) who had a demolition party and destroyed every internal wall in the house. The owner rebuilt badly, and one night the ceiling collapsed, fortunately missing me but unfortunately smashing the ETI case and its keyboard. I lost heart in the project, and the new generation of polyphonic instruments with memory had made it a white elephant.
It is a lovely big old thing, four VCOs, five mixers, three envelope generators, two VCFs, built like a tank but far from state-of-the-art now.
But recently I've been thinking about resurrecting the ETI 4600 again. Throw out the dodgy circuitry but use the panel and patch bay, which are both things I like. I've got two choices, I guess.
The first is whether to just use the panel as a MIDI control surface: attach the pots to a MIDI digital interface and use it to drive an ETI 4600 simulation that I would then construct using SynthEdit VST on my notebook. The trouble is that the thing has over 90 knobs and a 22x22 matrix switch.
The second choice is to replace the circuitry with something more modern. The leading contender seems to be the ASM-2 single board modular synth, which pretty well matches the ETI 4600 spec. I could add a MIDI controller or fix up the keyboard controller, or even add a ribbon controller I guess (halfway to a Mixturtrautonium!).
Sniffing around, it seems that two of the leading lights in PCBs or kit design and supply for analogue* synths are neighbours of mine: Elby Designs near Woy Woy, and miniature horse lover Ken Stone, in Victoria. Ken also started off with an ETI 4600 too!
The other sites that filled in important blanks for me (not that I have decided to go ahead with it!) are
What a great world this is! If I want to, all these resources are readily available. And I can prototype many circuit ideas in SynthEdit (for example, today I had a great idea for a simple circuit that would give resonant filter bank effects using much simpler component, and was able to try it out with SynthEdit...so I could work out the spec without even touching a soldering iron.), and get the building bug out of my system without even spending a buck! Err, there's the rub...the virtual synths are whetting my appetite for real construction as much as they are assuaging it.
Finally, I need to mention a hilarious fan site for synths: MatrixSynth's blog.
* Aussie spelling!
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Comments (19)
Read More Entries by Rick Jelliffe.
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hello all,
very impressed with this webpage, it is the most informative on the eti 4600 i've seen. i am seriously thinking of building one of these but i am not sure how worthwhile it would be with only the 12db multimode filters. anybody have the documentation for the revised 24db one? who likes the originals?
Whoop John: I'd love to get more details. I have the PDF for the 4600 in the UK edition as supplied by Maplin, and I am still trying to locate my Australian original 4600 book. But I would really like the 5600 PDF if it is available, because it has some features (sync?) I'd like.
Hi Rick, Whoop John here. Just stumbled back to see how you are getting on with the 4600. There is not much I don't know about these machines. I also built a 5600 at one time.
I rewired the 4600 so that all the leads were screened and attached to earth at the patchboard only on a metal rail around it. This got rid of a lot of the beehiving.
I think you should build a set of new modules with a mixer input on each one. Although you have 5 mixers on the 4600 it's never enough for what you might be able to do if you had one on each input with a bunch of sockets.
I have the original ETI magazine articles and the black and white PCB layouts for the 4600 modules. I have the PDF but you have that already. Do you have the 5600 manual? I can send.
I am having a lot of success home etching PCBs, so that is an avenue to go down. The boards are not that complicated and single-sided.
jukenutatbueyonderdotcodotuk
I have been thinking about what it would take to make a modern version of the 4600. Here's a stab:
1) ASM-2 board (2VCO, 2LFO, 2 VCF, 2 ADSR, 2 VCA, Noise, S&H, lag). This is rather than the 4 VCO and it is expo controls not linear for the VCO.
2) CGS mixer. This is 5 channel so it would squeeze the layout a little, or split off the extra 2 channels and follow the old panel design. Or vary the design and use a Ray Wilson stereo mix and get the headphone amp that way.
3) Midi-CV interface (Paia?) with portamento
4) Accutronics reverb
5) 5 channel EQ (any kit)
6) Headphone amp (any kit)
7) Input buffer and output buffer (any simple op-amp design)
8) Get original EG board plus extra VCA board from RCS and made up a complex generator as in the original
9) 22pin matrix board; still available from the Swiss firm.
Probably for the cabinet you would use two side-by side 6U rack modules, nowadays. So the total cost would be between $1500 and $2500, depending on how much you spend on cabinetry and panels.
The more I look at the layout or the 4600 the more it like it is intended as a kind of midpoint between the EMS VCS3 and the Synthi-100: a VCS-3 plus one more of everything.
I'm trying to get hold of some of the Cliff K2 knobs, to see if they make the thing look more Synthi-100 like! :-) And I think the Synthi-100's design aesthetic is drawn from IBM System/360 design, with horizontal rows of switches on a spacy white background.
I've just had delivery of a Paia MIDI kit and their dual Accutronic based reverb units. That will help supply the most important missing pieces. Unfortunately, their Hz/V converter is unavailable now: they told me it may be available later in the year.
Paul: If you want to scan the extra 3600 info, that would be great! It all helps.
In other 4600 news, there have been two 4600s sold on Ebay in Australia in the last couple of months, and one Maplin 4600 in England. The ones here were not completely working, but one was a little exotic with two keyboards and sold for about AU$1500 if I recall correctly. The other (black face) only made about AU$750 which is very low: a real bargain actually. I would love to get another, or even just another panel/matrix because I have quite a few non-4600 modules semi-built that need a home.
Well done, I built, and still have an ETI3600 with a few bells and wistles, the next thing is to add a MIDI input to it, should be trivial as the keyboard controller is allready digital.....famous last words !
I believe I have the extra info for the costruction notes on the 3600, I can get it scanned if you like.
Cheers
Lex - BTW your photos show your filters have LP/BP/HP switch, indicating they are the earlier 12db/octave filters. There was a later rethink of the filters (see PDF under the 3600 filter) changing them to 24db/octave but LP only. The sharper cutoff slope is good, but you lose the bandpass & highpass modes.
- cheers, Brian
Hi Lex,
only just noticed your question.
I've emailed you the 4600 manual PDF directly & will soon post it on my site.
I found the manual online but no longer remember where I found it.
Anyway I've started a collection of info for anyone mad enough to be restoring a 4600 and will soon add the PDF & other info to the site.
Check these occassionally for fresh updates re the 4600 ...
http://www.futuresoftware.com.au/synthesis.htm
http://www.futuresoftware.com.au/synthETI4600.htm
Rick & I are both in Sydney (inner west), whereabouts are you ?
I'm thinking of starting an Analogues Anonymous group :)
Good luck with your repairs. If theres been physical damage, I suggest unplug all modules from the power & bring them up 1 by 1, checking the power voltages each time. Otherwise 1 faulty module can shutdown some of the power rails as the PS goes into selfprotection mode, causing other good modules to appear faulty spuriosly. Other 2 cents worth - always suspect old tantalum capacitors of being leaky or shorted, and reseat all socketed IC's. Contrary to Old Crows (excellent) advice, I've had little problems with old 4000 series CMOS, but he is totally spot on about old tantalums.
cheers, brian(at)future(dot)software(dot)com(dot)au
I have a 4600, when I got it the power supply was burned out. I got his fixed and was rewarded with a fully functioning synth.
Great oscillators, crappy filters!
The synth was on a shelf that came off the wall resulting in the synth falling 3 feet. Since this incident only 2 of my oscillators work, I've been looking for a manual for ages, can the person who mentioned that had a pdf please send me a copy?
thanks, alexiscousins(at)hotmail(dot)com
I dusted off the mighty 4600 and powered it up tonight, following Bruan's procedure.
First, the good news.
* case looks better than I remembered
* no smoke
* power on all supplies: it seems about 10% shy of what it is supposed to be however...I'll try another meter but maybe I need to replace some caps in the power supply
* output module produces headphone output OK
* 3 oscillators work
* mixed works
Now the bad news:
* 2 VCA/Ring Mod don't work
* 2 VCF don't work (one has a torn-off power cable so I didn't try it)
* almost all the pots are really scratchy and will need replacing: that's almost 100 pots
* I really don't like the wiring to the matrix, I think I'll start it again
* need to get the thing properly grounded
Incomplete (need ICs populating or keyboard) and untested
* keyboard controller
* noise/exponential
* 1 x VCO
* 3 x EG
* 1 x VCA (on the EG)
* External input
* EQ/Reverb
* Joystick
Wow, I had no idea the boards were still available (or, at least, on the catalog)1 Boards from 1973: that must be some kind of record! The URL had changed, to http://www.rcsradio.com.au/ then look up Master list and find string "music syn"
Thanks so much, Brian
Rick,
VCF - PCB "ETI 601 H" is the original LP/HP/BP 12db/octave VCF for the 4600. I think Ken's comments re a missing link or wrong trace apply only to this board (???). "ETI 601 R" is the revised LP only 24db/octave VCF with resonance control intended for the 3600. The 2 units are interchangeable apart from front panel labels, both are based around high freq chopping of a fixed cap in/out of circuit, with VC controlling the duty ratio of the chopping to simulate a VC capacitor. From there the filter design is like any other simple RC filter network. The steeper cutoff gives better sound, and LP is more commonly needed than HP or BP at least in subtractive synth. The chopping circuit can be cantankerous & can intrude audibly if below 20kHz. This module is fussier about specific chip performance & wiring layout than others. Mine used to work & will again :)
The original ETI kbd ctrlr had many problems, with various add-on boards kludged on like band-aids. I've only had the Fairlight replacement board (KM-576, NG-576) which digitally scans the key matrix, and latches the key number. There are 2 distinct sections, and the latched key number is fed into what is basically an exponential DAC, the binary key id is demuxed to a choose-1 analogue switch, which selects the relevant multiturn trimpot voltage. It's very stable once calibrated. This was a premanufactured module from Jaycar in the late 70's, though ironically it had more capacitor failures and trimpot failures than my hand wired ones. It lends itself to separation of the DAC from the scanner, as a means of interfacing MIDI note numbers without depending on a separate exponential convertor.
Some boards are still availabe from RCS Radio
www.cia.com.au/rcsradio
I have the 4600 manual as a PDF, cannot remember where I found it online, but will email it to you. The ETI 4600 became the Maplin 5600 in UK with some mods, google will show lots of refs.
Hi Brian, thanks for the info, I'll follow the approach you suggest. According to Ken Stone's web pages, the filters had incorrect PCB, so I certainly would be interested in knowing any fixes! I am checking my old chest tomorrow (which has migrated to a different city), where I think the circuit diagram book was, but it would be great if you know of any alternative source of scans! (My email is r followed by jelliffe over a allette.com.au)
I have the old keyboard controller circuitry, but I really don't think I'll resurrect it: not much point when velocity sensitive MIDI is available. The Fairlight option sounds fun, if only because I actually was offered a job with Fairlight in the late 80s to work on their hard disk audio recorder (I ended up going to Japan instead, but two of my workmates there were ex-Fairlight engineers...small world!)
Hi Rick,
I'm also restoring an old ETI4600 that I partly built long ago, fixing things + adding stuff.
Ken Stone was a big help with some spare boards he didn't want, plus his own circuits are good food for thought and have many improvements and unique ideas. Thanks Ken.
If you proceed with restoring your 4600 I'd be happy to swap notes or help debug problems. Alternatively if you ever want to part with it let me know.
Some quick thoughts for your first time power up :
1 - unplug all modules from the power supply
2 - fire up the power supply only, check all voltage levels +/- 14, +/- 7, +5, check for heat, smoke, blown caps etc. Ideally, after 30 years, replace all power supply caps, especially the tantalums. Of course on the 4600 power supply this requires removing the heatsink backplate & is tedious.
3 - when all is well, plug in 1 module at a time, checking all power rails voltages each time. If the rails drop voltage, it;s due to overcurrent limiting, and probably caused by leaky tantalum decoupling caps on the module. Cutting suspect caps in 1 lead will identify which it is, or you can just replace all tantalums (as Old Crow advises).
4 - bring up say 1 VCO, mixer, Kbd ctlr, output, envelope, as a basic operational system.
5 - get that much stable & recalibrated, then bring on the rest, one module at a time.
Servisol brand "Electrical Clean & Lube" spray can works wonders on scratchy pots. (NOT WD40)
Most problems I've had have been failed, shorted, or leaky tantalum caps, as Old Crow advises. Replace all tantalums with modern electrolytics.
While Old Crow says the 4000 series CMOS chips will give trouble, in practice I found they are mostly still working fine.
Do you have the original flaky ETI keyboard controller, or the digital scanning Fairlight designed replacement ? I can post a calibration procedure for the Fairlight if wanted + some corrections to their layout.
The original VCF was lp/hp/bandpass selectable 12db/octave, the improved VCF was lp only, 24db/octave, with resonance control.
Good luck
Whoop John: thanks! Your MIDI controller info confirms what I thought. (I see Kenton has a kit for MIDI-ing up the Roland SH-3A...hmmm, maybe that is a nice project too...except the schematics for the 3A floating around are incomplete in the area of the wave generation sliders)
I already had put in the sync mod, and added a peak control for the ADSR, and the dedicated PWM LFOs is a good idea. I was thinking of adding overload into the mixers too. I have still never knowingly heard a sample of the 4600 VCF (which Ken Stone likes for some uses) let alone the 5600 VCF. Any chance of an MP3 sample?
Actually, I am not sure what is going on with the VCFs: the front panel has the top row knob labelled resonance, but the module actually has a switch which seems to be HP/BP/LP.
In any case, ultimately it would be trivial to have a switch with a lot of different VCFs: the designs for Moog, Arp, EMS, Steiner, Roland/Polyfusion, Buchla, Korg and so on are all available now that patents have expired: hobbyists have made versions with modern components for most of them too.
The only ones I'd like to see but I cannot find buildable schematrics for are the Yamaha GX and CS filters: Old Crow sells the filters (through MOTM from memory) and put an amazing amount of effort into reverse-engineering (organic solvents to disolve the pack) so I don't suppose that would happen soon.
I looked at the circuits again, and I found that actually the electronics are about 95% built. I will power it up over Christmas and see what smokes, but I think I'll try to get it going rather than use it as a MIDI control surface.
(On the subject of control surfaces, that's what I've been playing with: I took a Velleman USB DAC/ADC kit and made a box, and made my own stereo pressure/ribbon controllers using dual gang linear pots and conductive foam. It should be finished this week, and I'll blog on it, but I found I can use the pressure pads underneath a free standing MIDI controller to give (channel) pressure sensitivity. DIY is fun!)
Sage brooks: you should contact Tom at EFM, or the sdiy list for construction issues.
problems with efm wildcat rev2 components help
I have a 4600. I rebuilt it a few years ago. I used a Kenton Pro Solo with it and later a Pro 2000 MIDI interface, both recommended, and this overcame the huge problem of tuning the 4600's keboard controller.
I also recommend building the LP filter from the 5600 and replacing one of the 4600 filters with it. Also do the VCO sync mod from the 5600 and add pulse width mod to the square wave on the VCOs. I added a couple of simple LFOs just for this purpose.
whoopatblueyonderdotcodotuk