Need help with polyphonic Cmos 40106 project

[douthet]

I am currently trying to create a full polyphonic cmos 40106 synth with these features:
- Polyphonic(40106 cmos chip)
- (If possible) Square, Triangle, Sine, Saw wave (switch between them if possible)
- Cut Off Filter (Low Pass/ High Pass)
- Volume
- Envelope ADSR (I only really need attack and release)

Could anyone offer any schematics they have found on any of those features? And where to acquire the parts for that synth. Also your suggestions and help on how to go about this would be greatly appreciated!

I am using an old Thomas Compucon Alpha 1 organ for the keybed, I can give pictures of the perfboard used in the organ if needed. I got the idea from the C-MOnSter synth https://www.youtube.com/watch?v=PdIKnMvOMps[/url]

Thanks!

[PHOBoS]

[douthet]

Thanks for the reply and the advice! What chip would you recommend for the double inverter, what model? Also how would you assign the 12 roots notes to your keys? Is there still a need for a 4040 divider? Is there any schematics on that?

I am using a key bed with 44 notes.

thanks again

[umschmitt]

Hi! The guy from the video you posted is Cynosure here (and a site admin!). You could consider contacting him if not already done…

[PHOBoS]

[JovianPyx]

I'd like to make a comment about the CMOnSter synth as one of Cynosure's technical advisers.

It is a rather large project which was done in a way that is quite common in DIY synth electronics - creeping features. That is, it started as something rather small and then "Hey, I have an idea" and another piece was added, and another etc. One thing of note is that the PSU was underestimated (as in too small) and used a virtual ground. Now I know a lot of people are going to groan "Oh no, not again", but this particular project is an example of why you want to avoid virtual ground as much as possible. The reason for the virtual ground was the desire to use a single supply, but many circuits need a reference point between the + and - poles of the supply. A virtual ground can be used to accomplish this - but there are limitations. In the case of the CMOnSter, as the project grew, it became more and more unstable and unpredictable to the point that when things were added, older working bits quit working or changed in a not so good way. This is because a virtual ground cannot handle very much current going into or out of it resulting in a ground reference that jumped around. This introduces noise and other problems into the circuits. My suggestion to Cynosure was to replace the single voltage supply with a true bipolar (two voltage) supply. I believe that Cynosure chose +5 and -5 for this. This kind of supply creates a real ground between the two PSU outputs, but this ground is far more stable than any virtual ground can be and caused the synth to stop behaving erratically.

So my advice, since this will be a big project, start by making a good bipolar power supply. Standard 3 terminal regulators are easy to use and most can handle one ampere easily. In the long run, this will save you a pile of headaches.

[douthet]

My Goal for this synth is to be a pretty basic full polyphonic synth that could almost be used as a pad. Maybe almost like synthy organ tones at times. Any suggestions on how to achieve that?

So should my course of action be: Bipolar input --> Volume --> CD4520 --> octave divider (4024) --> 4040 divider --> 44 keys --> Gate (AR) --> mix --> Cutoff --> Output

Or did i get something incorrect with the order? is my setup simple enough that I may not need bipolar? How is the 4520 better for 44 keys?

I also came across what appeared to be some oscillators in the organ with a 5080 and 5098 chip. Any knowledge or thoughts on those?

[PHOBoS]

best/easiest option would probably be:
12 oscillators (CD4069) --> octave dividers (CD4520) --> 44 keys --> mix --> Envelope Generator (AR) + voltage controlled amplifier (VCA) --> Filter --> Volume --> Output.

or for 44 key polyphonic: here is an example of a 4 note polyphonic synth
12 oscillators (CD4069) --> octave dividers (CD4520) --> 44 keys --> 44x Filter (+ 44x control circuits) --> 44x AR + 44x VCA --> mix --> Volume --> Output
or you could use just 1 filter after the mix as with the previous setup.

[PHOBoS]

two things I just thought about.

If you put the envelope generator + VCA before the filter you can make a very simple VCA with just a diode and a resistor
and maybe an extra opamp. However if you put the filter before the VCA you would be better of with an OTA based VCA and
in that case a dual supply would definitely be adviced.

The other thing is that instead of oscillators and dividers you could use the CD4060 which is also a divider but it has the inverters
to make the oscillator already build in. So with 12 of those chips you could create all your notes. And because you only have
1 oscillator per chip there is less chance of them interfering with eachother.

[JovianPyx]

Pardon me if I don't understand something...

Do you already have plans for a keybed scanner and voice assigner?

A 4 voice polysynth needs to know what keys are being held down and what order they were pressed and released (so that you have a sensible instrument - example: what happens if you press more than 4 keys?). The voice assigner uses the keybed scan information to set pitch and octave values for the selected oscillator and also asserts a gate signal for that voice.

An AVR based arduino seems perfect for this and as an added benefit, the synth could respond to the 44 key keyboard as well as MIDI input (if you want to add that).

[PHOBoS]

[JovianPyx]

Ok, not a 4 voice. More like an organ. Indeed, I did not understand.

[douthet]

[PHOBoS]

[JovianPyx]

Interesting IC the 4060, oscillator plus divider chain. I wonder why they decided not to bring O0, O1 and O2 out to pins...

Perfect for top octave oscillator and dividers.

[douthet]

Thanks again PHOBoS and JovianPyx for all your help with this.

So from what I can see about the 4060 is that it has 10 outputs, would that mean it has the potential for 10 octaves? So I would set up my root note and that would be sent from output 4 outputs (44 key) to each corresponding octave of that note or would my resistors and capacitors to determine the note go after the division of the 4060 chip?

[JovianPyx]

[richardc64]

Or, one could skip the tediousness of 12 calculations of R/C values and the expense of stable caps, stable metal-film resistors and trimpots, plus a perfboard big enough to contain all this stuff -- all of which in the end gives 12 oscillators that cannot have a Master Tuning that will maintain the equal tempered (or any other) relationship between all 12 oscillators -- and instead spend 40bucks for a modern top-octave replacement IC which needs only ONE oscillator.
http://www.organservice.com/crm/topdividers.htm#Fig5

Make a reasonable offer and I might be persuaded to part with one of my antique 50240s for considerably less $.

On the other hand, maybe one of the rocket surgeons from the Microcontroller forum could be persuaded to devise a pic or fpga top-octave generator and sell them!

(I always audibly groan when I see "polyphonic" and "40106" in the same sentence.)

[douthet]

[PHOBoS]

[richardc64]

[PHOBoS]

[PHOBoS]

Here's something. It doesn't have an external clock input though.
Hmm apparently I already downloaded this one before,
totally forgot I had that

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TOS1.txt
Description:	Octave synthesizer PIC program by Scott Rider	Download (listen)
Filename:	TOS1.txt
Filesize:	6.97 KB
Downloaded:	283 Time(s)

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[blue hell]

[PHOBoS]

Well it does use a standard crystal so it should indeed be possible to just replace that with a different oscillator.
Didn't think about that even though that's pretty much what I did with the EK2100.

edit: it even says in the code "16MHz crystal w/33pF caps or 16MHz clock to CLKI"