Jen SX2000 clone

I was wondering if anyone here already tried to clone an SX2000 from Jen?
I had this synth a few years back and it sounded really, really good. Now, I want it back to be my diy accordion synth.
You can find all the schematics easily and there are no strange components.
I am trying to start to try to do the pcb layout but I am not really good. I plan to do one board per page of the manual (maybe ot is not ideal).

manual with schematics

When I have all the schematics in kicad I will share it here.

for now I have only made the VCO

svg file of te VCO

Any(thing) help is welcome
have a nice day :sunny:


Still on it… Here is wiser and smaller PCB for the VCO. Soon to be tested.

Any input is welcome. I can provide the files for those who would be interested. It’s a great sounding VCO, if it works :slight_smile:

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… if it works … :thinking:

I appreciate that you have taken on this synthesizer. Whenever I am through wioth all my projects I have an urge to start cloning the JEN SX1000 synthesizer. I’ve got the M110 chip lying and waiting (that’s the kbd decoder/VCO).
I will follow your work with this synth.

PS. I found a description of a DIY synth based on the M110 chip in italian magazine Nuova Elettronica.

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Thank you.

I am not a king of organisation so I must apologize in advance.
When I have the first parts working I will bring all informations here.
The SX1000 and SX2000 are very different machines. On the SX2000, the hardest parts to find would be the LM310 and my guess is that, in this circuit, it is easily replaced. Other than that it’s all 741’s and old transistors. Very old school and simple circuit.
I want to do something that can be repaired forever :slight_smile:
I am about to send the pcb to be made.
When they are populated and working my second task will be to have four oscillators in order to have 4 voice of polyphony (or maybe five?). I am meeting a geeky geek friend today to talk about how to avoid arduino or any microcontroller (please mum no computer) and how it would be possible to do that with CD4xxx component series. I would like to be able to select 1 osc per note for 4 notes polyphony, 2 osc per note with 2 notes polyphony and 4 osc mono. Like a cheap monopoly.
Next week I get a broken elka concorde for parts to have an accordion style keyboard.

Ok so, i would be somehow pretty hard to achieve it with only logic. It would take a lot of space and a lot of components. So back to the arduino route.

You might want to look at the Powertran Polysynth, it is a 4 voice or 8 voice poly with a digital (non CPU) assigner.

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Oh Yeah, thank you.
That would be so great… And so big. For now I am going to try with a microcontroller mostly for the time, the flexibility and the space it permits to save as I would like it to be as compact as possible. I had too much to dream :grinning: with this starting project but I will do it, just not now. I fear it is far beyond my skills. Nevertheless it is my goal. As soon as the other boards are tested and running I am on it. I could even find some people interested around me. And it could even be a useful pcb to share.

I ran into EM&M’s Voice Board that is intended to work as single board synthesizer but also in a polysyth. Just wonder if anyone knows if such a machine has ever been made.

I think this was part of the Digisound 80 modular design. They also made a polyphonic controller, so in theory you could have made a Polysynth with the alphadac polyphonic controller and several voice cards, but I don’t think it was a popular option.

Yeah, I recall the CPU-based controller … Read somewhere that there was vital info lacking, but anyhow - NO COMPUTERY!

Just a crazy idea, could MFOS Soundlab or even Noise Toaster accordingly adopted been used for a polysynth?

Any complete voice card can be part of a Polysynth, the only common part really in a Polysynth is the LFO(s). It’s what some people do with Behringer mono synths, chain them into a poly. Same with things like the Oberheim 2, 4 and 8 voices, based on a SEM voice box but they tried to make it more usable with a programmer. What’s in an Oberheim OB8, 8 voice cards on a motherboard with a common LFO and a programmer.

I didn’t know the alphadac.
I should receive the polykit voices soon for the left hand of my accordion (is that you @craigyb?), the ones I have made from the jen for the right hand.
I have never made a keyboard synth from scratch, only modular. Now I realize that all that is important is finally What do I want on the frontpanel?
4 pots and a screen or a lot of pots? Do I take one vco to be the LFO? digital LFO? And how do I fit everything in the tiniest space.
Any ways still wainting for the boards and working on the motherboard to control them. I wat to keep the jen spirit : no midi no sequencer only an instrument who needs a hand :love_you_gesture:

I’m not PolyKit, although I have made extensive use of some of his designs and modded them to my requirements. I’m a big fan of a knob/button per function but like you said, real estate is tricky to manage. I also have an 8 screen 16 encoders design for editing but I don’t like that at all. Here are some of my front panels.


Thanks. These are beautiful machines. I guess the 8 screen has lost a bit of his soul compared to the others.
I have seen that you use DCO1 DCO2, I have seen this on other synths too. What does it mean considering the 6 voices?

The 8 screen synth is actually an incredibly powerful synth, 4 DCOs, dual filters, 4 envelopes, dual LFOs, multi effects etc with an arpeggiator and a sequencer, 32 note polyphonic and there are 2 of them in that box for dual and split sounds. But you are right, it’s a little soul less to program. I tried to make a knob per function but there are nearly 500 controls to use.

Basically 2 DCOs per voice can give you a thicker detuned sound, budget synths use 1 DCO or VCO per voice and compensate with a chorus unit. Most flagship synths are dual VCO or DCO per vouce, so 6 or 8 voices with two sound sources per voice. You can Detune one against the other for a pleasing sound. Some use dual VCOs or DCOs and still have a chorus, like my designs. Just think of a voice card with one extra oscillator at the front. Some even have 3 like the memory moog and the new Sequential circuits Tarragon or whatever it’s called.

A DCO design is inherently more stable and doesn’t suffer from pitch drift like analogue VCOs do. I noticed on polykits voice board if you combine them to make a Polysynth, how do you tune them and keep them in tune. Most analogue poly synths have an autotune routine to return drift out if the synth due to temperature etc.

I actually abandoned my VCO design due to the lack of autotune and replaced the oscillators with voltage controlled DCOs for stability. When I get a chance I would like to build an autotune routine into my polyphonic controller.

I have to say that I love your designs.


me too :slight_smile:

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Check out the schematic for the EDP WASP Synth all of the digital stuff was done with 4000B chips
, no CPU

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sorry I have not responded sooner.
I dug into CMOS science and this is really not for me. There is too much computation. And I am not going to take that road AT ALL.
Now the project is on hold. I had to pack all my stuff to move in a new house. I have to fix a lot of things in this house so electronics are in a box. BUT

I bought a broken SX2000, that i repaired and I want to add a reverb inside it.
Ideally I would to be able to switch between two modes :

  • the reverb is at the oupout (this works)
  • the reverb is before the VCA and takes the sound directly from the VCO (still testing, no good results for now)

after that I restart the cloning process.

anyways thanks