ALF MC16 compatible hybrid synthesizer

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stynx's picture
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Posts: 166

I'm currently working to implement a 3 voice synthesizer based on the ALF MC16 design.

It uses a 82c54 Timer (compatible to the 8253 on the ALF MC16) for the generation of the 3 voice frequencies as well as a TLC7226 quad DAC for the generation of the envelope control voltage (0-5V). Three CEM3396 dual oscillator "compete analog voice" chips are used for the generation of the actual sound. The CEM3396 has a logarithmic VCA control voltage (0-5V) input and several other CV (control voltages) for waveform, filter and linear gain. These additional inputs cannot be directly controlled by the ALF-software. Therefore I have to use potentiometers to create the CV externally (may be software controllable in a later version of my card).

The current state of the card is:
10.08.2017: built 2nd prototype card after testing the digital circuitry on a separate board. Added 10 potentiometer for 0-5V CV on an external control board.
11.08.2017: First test with 1 voice was successful.
11.08.2017: 2nd voice added and corrected some grounding issues. ..had to repair some loose wires.
12.08.2017: accidentally shorted GND and 5V and had to rebuild some of the digital circuitry.
13.08.2017: analog part of the 2nd voice is functional but the digital part seems to have a bug around the 8254 Timer and I have to fix it to continue. There TCL7226 DAC works like intended.

The Prototype-board in the attachment will have 3 voices with only one of the 2 oscillators per voice active. After the card has been tested successfully I will design a PCB and create the 1st pre-production prototype. On this card I will add a circuit to access the 2nd oscillator on the CEM3396.

The simple diagram included shows the connection of the chips.

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ALF_MC96.jpg372.37 KB

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stynx's picture
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Joined: Apr 19 2012
Posts: 166
Re: ALF MC16 compatible hybrid synthesizer

Posted on comp.sys.apple2:

On Sunday, August 13, 2017 at 11:02:15 PM UTC+2, Antoine Vignau wrote:

That is cool, Jonas.
Count me in for one, please, and keep up the good work,

Antoine

My response:

I'm only making a few (less than 10) for myself and some friends (you included)

The CEM3396 chips are about $10/piece at the moment with some of them being duds.
Combined with the other chips it will result in a price of about $100 without shipping, assembly or testing.
A sales price would be about $200 and I wouldn't make anything with that ...

Its just a fun project. When im finished, I will provide all the schematics and layouts that anyone can make their own. It will have the option to use an external control-board with potentiometers or an DAC-Module that will allow software control. The 3 voices will be coupled (3 voice polyphonic) by the parameters but could be controlled individually. The individual programmability of each chip would need about 30 DAC channels ... to much for a single card (even with a sample-and-hold approach). Therefore I will implement a simple solution with expandable options (via headers) to add these software controls (io-select range).

Configurability by software could be done by a simple basic-script that sets the values for each parameter:

  1. Waveform (for both oscillators A/B) 4 possible by 2bit select

  2. Pulsewidth A

  3. Pulsewidth B
  4. Waveshape A
  5. Waveshape B
  6. Oscillator balance A/B
  7. Filter Modulation (by oscillator A)
  8. Filter Frequency
  9. Filter Resonance

  10. Gain (volume control)

All to be controlled by either analog input or software control by 8bit words.

... but I have to get there first Tongue

possible waveshapes with cem3396:

-Jonas

stynx's picture
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Re: ALF MC16 compatible hybrid synthesizer

https://soundcloud.com/vintage-micro-music/alf-mc96-test-2-voices-cem3396

2 of 3 voices active (actually 2 of 6 since each cem3396 has 2 coupled voices)

-Jonas

stynx's picture
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Posts: 166
Re: ALF MC16 compatible hybrid synthesizer

complete 3/6 voices. full MC16 support:
https://soundcloud.com/vintage-micro-music/sets/mc96-apple-ii-analog

-Jonas