Analog Under Digital Control – Uneasy Task

[Pathfinder-33]

Hello All,

I want to thank everyone who helped me with my IC question.

Another idea, I am thinking about making an analog synthesizer(musical instrument) for electronic music. The synth will have at least 8 voices, each voice needs to have 2 VCOs, VCA and VCF.
I asked this question on dedicated DIY forum but no one answered it. My post had 150 views but no replies at all.
What could be the best solution for controlling analog voice boards(with VCO,VCA and VCF)? The synth has to have memory and auto-tune function since VoltageControlledOscillators are not very stable.
I know it sounds like very difficult project for DIY but I am very interested in it, I have time to learn new things.

A friendof mine gave me advice to disassemble EPROM of some existing analog synth, add or modify some functions and use it for my new synth.
This sounds interesting since I do have very good analog synthesizer with Z80 microprocessor and EPROM but the person who gave me this advice doesn't know how to do it or even where to begin.
Give me advice where to start, how to disassemble EPROM?

 

[blueroomelectronics]

Probably not worth the effort. You'll need an EPROM reader $$$ and some real Z80 experience to disassemble the code and document it.

Get some old Elektor back issues with the old Formant synth if you want to DIY a synth.
Elektor Formant Synthesizer Demo Synthtopia
**broken link removed**

 

[Pathfinder-33]

Formant synth looks pretty interesting, thanks.
Modular synth are nice, someday I will build modular system but I am a fan of polyphonic synthesizers with memory.
I will check the prices for EPROM readers\programmers, I think they shouldn't be too expensive nowdays.
Are there many different standards\types of EPROM?
It wouldn’t be nice to discover incompatibility after buying a device.

 

[blueroomelectronics]

I take it you're a very competent Z80 programmer. Modifying dissassembly is no simple task.

 

[kpatz]

Synthesizers are one of my passions.

Making an analog polysynth is a pretty daunting task though.

For digital control you would use a microprocessor or microcontroller, and to generate control voltages you would use a DAC and S/H cells to allow multiplexing of the DAC to generate the multitude of CVs you'll need.

Maybe start out making a monophonic synth and then work up from there.

I've had thoughts of doing something similar. But what I'm thinking of doing is starting with a synth kit, such as **broken link removed**, then building a digital control unit for it. The digital control would handle MIDI-to-CV conversion, and maybe throw in some digital envelope generators and LFOs. I would use a microcontroller, a DAC, and maybe 8-10 S/H cells so I can get a bunch of CVs to work with.

To do autotune, you would need to feed the VCO's output (probably the square/pulse wave) into an input on your micro, have it measure the frequency and adjust the tuning voltage to bring it into tune.

 

[ericgibbs]

Formant synth looks pretty interesting, thanks.
Modular synth are nice, someday I will build modular system but I am a fan of polyphonic synthesizers with memory.
I will check the prices for EPROM readers\programmers, I think they shouldn't be too expensive nowdays.
Are there many different standards\types of EPROM?
It wouldn’t be nice to discover incompatibility after buying a device.

hi,
If you are in the UK, I could read the Z80 EPROM you have already and do a disassembly file.

 

[Pathfinder-33]

hi,
If you are in the UK, I could read the Z80 EPROM you have already and do a disassembly file.

I am not in UK but probably I could send EPROM chips to you from my Roland Jupiter-8. There are 3 chips.

 

[kpatz]

You have a Jupiter-8... me jealous. Those things fetch insane prices on eBay nowadays.

 

[Pathfinder-33]

You have a Jupiter-8... me jealous. Those things fetch insane prices on eBay nowadays.

If we unite we can make a replica of Jupiter-8 with some interesting improvements. It could be open source project so anyone who loves analog synthesizers will be able to make one of the best machines ever made for him self. I was not able to find any DIY projects of polyphonic synthesizer.
May be I was not looking good enough, are there any?

 

[ericgibbs]

I am not in UK but probably I could send EPROM chips to you from my Roland Jupiter-8. There are 3 chips.

What is your location.?

 

[Pathfinder-33]

What is your location.?

Moscow Russia

 

[Nigel Goodwin]

Synthesizers are one of my passions.

Making an analog polysynth is a pretty daunting task though.

I binned a Korg one the other year, it had the usual leaking battery problem, and my daughter didn't seem interested in it - so I binned it rather than bothering repairing it.

 

[Pathfinder-33]

Was it Polysix?

 

[Pathfinder-33]

You'll need an EPROM reader $$$ and some real Z80 experience to disassemble the code and document it.

Isn't it possible to use some kind of program like Z80 SIMULATOR IDE link or Z80 Assembler/Disassembler **broken link removed** or some similar tool?

 

[Pathfinder-33]

Just found IDA Pro - Interactive Dis-Assembler, anyone tried it?

Here are EPROM images from Oberheim OBX poly synth and Roland Jupiter-6:
View attachment jp6rev6.zip

View attachment obx_ib_2732_sum_000472ad.zip

Can anyone make disassembly files?