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[Bogus Noise]

Yeah, I've got one of those. Opened to check it but it's currently unbent. I'm suspecting it's pretty much the same schematic as the more common 3-boards-sketchily-soldered-together ones.

[michael page]

I'm working on an EK-001, but i'm a bit of a proper electronics novice though.  I'm trying to get an output for both layers of the polyphony so i can filter them individually (and get an envelope shape from each one).  On the AK-900 circuit diagram there seems to be a transistor that looks like it inverts the signal before the amp chip.  I have a couple of versions of this keyboard (the 'all on one board type' and the 'three boards linked with lots of wires' version) but neither seem to have this transistor on them.

For the controls for each envelope ive got a A100k pot in parallel with a 10u or 100u capacitor (switchable for 2 ranges).  This is hooked up to replace or in parallel with the caps that control the env size from the diagram on this pdf: https://www.pololu.com/file/0J180/electronic_keyboard_kit.pdf

Any thoughts would be appreciate!

[Bogus Noise]

Sounds like you know more about electronics than a lot of benders!

I have a suspicion that the separate outs are exclusive to the IC version, and not any of the blobs, which mix them internally before they reach any solderable traces. If I recall right, the drums are on one output and both synth channels on the other, whereas the IC has individual outs for all 4 drums and both synth channels (though I've not yet encountered an IC version).

So you may be a bit stuck there. One thought, though it may not really go with the dual channel approach you want to take, is I recommend getting hold of a dual A100k pot for the envelope, it's nice being able to control the two in unison!

[michael page]

I think the blob ones do have both outs. They exit the chip via a pair of diodes. 

RE dual pots. I like to use single slide pots close together, that way you can slide them both together or wiggle them separately! I recently made a 12 voice synth with individual sliders for each voices level, filter and noise amount, with all the sliders bunched together : https://vimeo.com/146105323

[Bogus Noise]

Slide pots sounds a good approach for the way you're doing things. Personally I found it awkward to be playing the keyboard and have alternate notes sound different, but it's entirely a stylistic choice. Checked the video, that 12 voice sounds cool!

Here's how mine turned out btw :-)

https://www.youtube.com/watch?v=u7tOLv01S60

[michael page]

Wow devastating!

Im making some slow but useful progress with my research.  Ive got a super simple env response from each voice by putting LEDs in instead of the diodes on the board.  These will be coupled with LDRs on a filter circuit with switches to change if it envelopes itself or the other voice.  Im trying to find a full A-101-1 filter schematic (Preferably one modified so it can run on something other than +/- 15v). 

I'll report back...

[michael page]

Inspired by the way http://www.noystoise.com/ reverse engineers synths from toy ICs and the way http://gieskes.nl/ does manhattan style soldering, I decided to try and do this with my hing hon chip. So ive built the basic bits to make it go from the ak-900 schematic and it can parp out notes and change instruments and play the demo etc (and added envelope size control).  Ive worked out a simple resonant filter circuit that I can make a pair of for each voice of the polyphony.
I now want to modulate each of these by vactols paired with LEDs that follow the two envelopes, and an LFO.

Heres how its looking so far... :

[michael page]

and heres how it sounds.  Its with drums obvs : https://soundcloud.com/michaelanimationpage/band-and-new-synth-test

https://vimeo.com/161904129