I was going to post schematics and scope traces here but I’m only allowed one image
But the period is running from 50ms to 15s which matches the design (0.06 to 20Hz) and the waveforms and peak-to-peak values look correct for the triangle, sine and square waves.
So I’m feeling rather chuffed. I’d appreciate feedback if I’ve made any mistakes.
Connecting it to the 2600 I notice that the outputs need to be buffered, especially at low frequencies.
I figure if I want to make this into a module then I’ll need a couple of enhancements:
The square wave outputs need to be buffered.
The sine wave output needs to be amplified to 10V (or should that 12V?).
And I’m tempted to make the sine output bypassable so I can still use a ‘true’ T2000 value (or would it make more sense to add extra attenuation the VCO input?
And on the input side I’d like to be able to add voltage control. I’m guessing that would be an extra input to IC32 pin 2? I’m watching the Moritz Klein stuff on YouTube and I think he’s covered that in the VCO build using an NPN transistor. I’ll have to research but I’ll happily take guidance on that.
My first analogue synth was a Jen sx1000 which seems very similar to this. (Are they related?)
I’m tempted to build the whole 2000; keys, knobs and a mono out. Something you can abuse/play without a screen or menu.
And here’s the Transcendent 2000 noise generator. I’ve rejigged it to use 4015 shift registers instead of the 4006 and moved a couple of components that make more sense in the VCF. Before:
The clock circuit is running a little slow, 11kHz as opposed to 30kHz claimed in the docs. I wonder if this is caused by the breadboard? I may need to experiment with component values when I get to the PCB stage. Also, I used a 47nF for C44 as I didn’t have a 33nF to hand. I assume that won’t make a significant difference though.
I really wanted the WHOLE thing, so the board’s are more or less according to the original and covers the whole synthesizer.
I had some vague ideas to “cut the board in pieces” and “modulate” it, but I am lazy and understood that just by processing the baord bit by bit wasn’t easy as the components are in many cases spread out all over the board.
Interesting. Are you designing from schematics or copying the original board layout?
My own project is slowly moving forward. I just haven’t added any updates here. I just about to send the second revision of the AD/ADSR/VCA module to the fab - the first had a few issues with my copy of the schematics, and I used the wrong footprint for all the transistors and made some false assumptions about necessary trigger levels.
More or less copying the original board but making changes for use of other switches, other transistors and other PTC’s (1K). Also had to squeeze the board an inch to a length of 500mm.
Also made id 2-sided and accordingly made some changes for the traces.
It sounds like you’ve noticed that some of the footprints are different these days (in particular the BC212 and BC182 - the board uses footprints for the BC212L and BC182L).
Are you updating any of the no longer available components? The only one I can’t seem to find a modern equivalent for is the LM748 used in the VCO.
I planned on using 2N3904/06 so the board is made to accept those instead of the BC182/212 (that are, over here much more expensive).
As I have some 748’s lying around I planned to use them. I guess small alterations can be made for other OPAmps. I don’t think the choice is that critical.
Also the 3080 are obsolete, but are now produced by a Latvian company, so you can get hold of them.
