Transcendent T2000 Clone

The Transcendent T2000 synthesizer was a DIY synth, presented in a few issues of ETI in July and August 1978. The designer was Tim Orr and a complete kit was sold by Powertran.
It could be considered as the smallest siblings among the ETI synthesizers like the 3600, 4600 and big brother/sister 5600, but wasn’t really accepted into that range.
Well, others are better at telling the history so I tell mine.

The T2000 has ONE VCO, a VCF, VCA, Noise source, LFO and one AR for the VCF and a ADSR for the VCA. It also has a 37-key keyboard.
It is small portable and (spoiler alert) it makes great sounds … and it is simpel.

Actually I started looking into this one (and Radio Shacks Concertmate MG-1) four years ago as they both looked easy enuff to clone, but I brought home an MG-1 from USA a few years ago leaving the T2000 in the “tube”.
When we add a new project plan to our list we “put it in a tube” … a Swedish saying, at least.

First of all - I had a pretty good collection of various semiconductors requiring nothing (except the CD4006) for this one (I’ve got pretty much all semiconductors for the MG-1 as well) and I have nice program for making PCB layouts (Sprint-Layout 6.0). It’s an easy-to-use program where you can have a back-drop (a bitmap image of a PCB you want to clone). It is also a very basic program, but for simple projects it is absolutely perfect.

Some short notes on the process and my progress.
I did start layouting the … layout a few times but ran into some problems as I had to (digitally) glue together pieces of the original board and somewhere was half an inch missing. Also the switches were not to be found anywhere and trying to fit an ordinary 2-pole 3-way toggle switch became a problem for me. So I made some attempts, lost interest, probably deleted half-finished work.

The final attack on the summit started early this Fall and with help from nice fellas, among them Telefunkian who has made a series of Youtube-videos, I could fill in the missing pieces, reach the peak and plant a Swedish flag on the top of Tarakoram-2000.
I even did check the PCB for errors several times before shipping the gerber-files to JLCPCB.

Normally when I loose my head, I start out grandiously, presenting a MEGA-project and then I sort of loose steam pressure and stall and leave yet another great but unfinished project behind me. This time I will try to get myself together and see if I can finish this one through, sharing experiences, photos and frustration (and noise) with you.

Have to fix me something to eat, but here’s the ETI articles on the machine: Transcendent T2000.pdf.

OK! OK! OK! Here’s a picture …

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Have to wait a few minutes more for the potatoes so …

My modififications:
The original PCB was some 10-15 mm too long for my program so I had to squeeze it a bit (no problem doing that).
Made the board 2-sided.
As I couldn’t find any slide switches I went for the type used in the MG-1 (ordered a pack from AliExpress … two packs). That meant a slide change in footprint.
remade the board för transistors 2N3904/06 instead of BC182/212.
Swapped the skeleton trimmers to multiturn.
Also swapped the Cu-wire resistors to (modern) 1K PTC resistors and placing them as close to the CA3046s as I could.
Else tried to make marks and notes to the PCB to simplify things.

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And there’s already a tiny little problem. Look at the first photo. The potentiometer axle is too short :roll_eyes:.
I have for another project an aluminium tube, outer dia 6mm. It is possible to joint the axles with short pieces of the tube.

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I forgot the links to the switchjes I picked for this project. These are the ones I bought from the shop in the links below. There are of course other shops on AliX that sells that kind of switches but beware as there are similar switches aimed as spareparts for various Pioneer or Sansui recievers, selling for $10 or more A PIECE. Those listed below are at around $6 for 10 switches (VAT and shipping extra).

The 2-pole 2-way switch
The 2-pole 3-way switch

Here’s a photo of a section of the MG-1 with the same switches mounted. My only objection is that the switches flips at a slightly too large angle.

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so your building a clone T2000?

how you planning on doing the keybed?

Keybed … ??? DO I NEED KEYS??? :cold_face: :cold_face: :cold_face:

OUCH!!!

Cereasly, I need some coffe and then I will tell you a little about my plans, problems and solutions.

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I got two keyboards salvaged from an old organ. The one I plan to use has 41 keys and will fit my project pretty good:

I was a bit worried about the 41 keys I have to the 37 keys in the original. What values for the resistors in between key contacts to use? How to calculate currents and voltages and then I realised that I have no problem at all. This should work out fine, I believe:

The original BOM says 37 resistors, but they only go to 36 places. My values will maybe have to be changed 25 Ohms.

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From the article the resistors are 27.4R, not 24.7R.

In the original you have +12 V going into an inverting amplifier whose gain is (680+27.4n)/4750, where n is from 0 to 36, so the change in output from n to n+1 is 12*27.4/4750 = 69.2 mV. That corresponds to 0.83 V/oct and I don’t see where it gets rescaled to 1 V/oct. … ??

The output voltage ranges from 12*680/4750 = 1.7179 V to 12*(680+36*27.4)/4750 = 4.2099 V.

For 41 keys I’d think you could keep the resistances the same and just get a range of 1.7179 V to 12*(680+40*27.4) = 4.4867 V. Or you could reduce the 680 by 4*27.4 to 570.4 and get a range from 1.441 V to 4.2099 V. Either way still 0.83 V/oct.

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My bad. And I haven’t ordered these resistors yet.

I think it is mentioned (have read these papers many times over) about the non 1V/oct. Also the CV input is according to the T2000 “standard”. And I read that using external CV isn’t that simple either, but that’s another story.

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Got most of the components for the VCO in place this morning. Has to reorder a few resistor values and will quadruppel check the FETs. Haven’t got the originals but a bunch that ought to work as equivalents, like MPF102, PN4391, 2N5457, 2N7000 etc.
Switch and potentiometers attached for the photo. Note the use of silver-solder!

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