DIY semi-modular, 80% mfos

[frotje]

Hi,

So i got sounds out of my semi modular synth, so it's time to share some images (and later on some sounds of coarse).

Build the following:
- 3x VCO (MFOS)
- Phase shifter (MFOS)
- 2x VCA (MFOS)
- Ring mixer (some other parts but basics MFOS)
- 24db low pass filter (MFOS)
- 3x LFO (www.electricdruid.com)
- 3x ADSR (www.electricdruid.com)
- noise source (www.electricdruid.com)
- joystick with quadrant and xy output (somewhere form the internet)
- midi interface (m.bareille.free.fr)

Midi interface still needs some debugging and i ordered an extra low-, band- and highpass filter at mfos which i plan to place in parallel of the 24db low pass. (using stereo pots, same input and seperate outputs)

I bought a Behringer patch panel for 45 euros from which i desoldered the jack plugs. (about 100 pieces)

Used shielded cables for all signal paths.

Sound samples will be posted soon...

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[v-un-v]

Nice!

[ashleym]

Great looking unit and an interesting layout.

I was going to ask where you got the joystick from but I see it was "the internet"!! How did the Electric Druid designs go? I have the chips and a programmer but I am struggling to get the 2 working.

I have zoomed in on the pictures and I can only see one mixer for the oscillators. Is there more than one for audio, eg send some unfiltered sound to the output? Do you have one for mixing modulation signals?

Did you think of some sort of wavefolder or distortion?
http://www.oakleysound.com/discon.htm

Finally(!) I like your idea for the filter using the twin pots. Adding a high pass to a good mix of oscillators sounds powerful. I await the results with relish.

Please take my comments as constructive only, there is no disrespect to your marvellous synth!!

[frotje]

Hi ashleym,

I always like comments, which might inspire me for additional changes, so thanks. But i wanted to have a design target so i could stop of adding more functionality. (this project should have an end somewhere

I simply used the circuit diagrams of Tom Wiltshire (electric druid).
I liked those since i had some experience with pic chips already.
So, just program the chip, and build the filter. They work all fine in my synth. (i've tested them all seperately before integrating it in the synt)
You might need a scope to check the signals and to find faults.

Indeed i have one mixer, which is part of the low pass filter.
I have been thinking to use a simple switch to route the mixers sum signal directly to the output. (i still might implement this)

Now i planned to add the state variable fiter. (just to get some more higher frequencies in place).
Will put it parallel to the current low pass filter, but with seperate outputs.
Have some schematics of the diode ladder filters used in synthi ems synths which i also would like to 'test'.

I'll try to post a picture of the joystick control, but i have to make a drawing. (i lost the original internet link somehow). It is a set of opamps that output the differences of the X and Y signals. I also made some mods to get the output range -5 to +5 volts.

[frotje]

Ok, found the joystick control schematic.
(it had been posted somewhere in electro-music.com

I had to place new pots in the joystick since i broke the original ones when trying to correct for the centre position.
After installing new pots (100K lin) i first measured the voltage range.
This is needed because the pots are only operated at a limited range.
I also centered the pots so that the middle position would give 0 volts.
The range appeared to be +/- 1 Volt. So i modified the feedback resistors
to match an output of +/- 5 volts.

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[ashleym]

That looks very interesting.

As you say there is an issue with the limited range of movement of the pots in a joystick. Frustrating but you can understand because of their construction.

I see a few ways of using a joystick; the voltage generator as you describe, also I would use them as a direct pot on an output ie like a volume control or a 4 way mixer with inputs to each end of the pots and a centre pin mix out etc etc. I can suggest these because I am using single ended connections on my Ultimate based synth meaning I can have passive banana ins and outs. Looking out your buffered schemes there is food for thought.

[frotje]

....you could buy two additional dual VCA pcb's from mfos and connect them to the joystick outputs.

[frotje]

Some sound samples i've recorded.
Used a little reverb/echo from my mixer.

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[Skrog Productions]

looking great , nice neat layout inside .

Your synth would be great for 2 user performance like a synth version of the old desktop game "battleship" .


look forward to hearing your sounds

Dave.

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[Skrog Productions]

exellent work , i really like those ring mod sounds , this synth will keep you entertained for ages

Dave.