Tuesday, January 25, 2011

Monotron Modifications Continue...

Prototype board manufactured!
Design for board from here:
Now, since I drilled, pressed on the etch resist and finally etched out the circuit board using some chemicals, an updated design was posted. I'm still going ahead with the old design.
Square wave, PWM, noise gate, clean audio out board

Etching off the copper...


Transparent view - all holes drilled.
  Components to follow... I still need to get some board mount knobs that match the monotron knobs (suggestions welcome) - I already stripped a monotron (to use as second VCO) and used three of the knobs on remote board (see earlier post), but don't want to buy a 3rd monotron just for knobs - plus they're not that easy to remove (when your green like me!).
The extra knob-mount point (to right side of board in last pic) is intended for "glide" control in conjunction with the midi mod on monotron++. I'm not doing the midi upgrade, so instead I'm going to mount a keyboard tracking depth knob (as I did with the Gakken) since its a bit more versatile than just a keyboard tracking switch at a fixed resistance; will probably put switch too.

Thursday, January 6, 2011

Monotron - Remote Knobs for VCO&LFO2 and Stripped Monotron

Here's the remote board to hold the knobs. The middle was going to be the clear LFO rate knob, but I broke it in the process of trying to recreate LED and attaching it with super glue. Well actually it was when I filed the underside to get rid of excess glue and messed up the central pivot (axis pole), and now the wiper jogs off the resistive tracks inside! So I'll have to do a surface mount LED for LFO2 rate.

Remote knob board
 I sat the knobs higher to give space for switches.

Here's the stripped monotron:
Stripped out power supply, jacks, vol. wheel, and knobs
Tried to photograph all the circuitry to create a map - to match up Korg's schematic, but camera is a bit crap:

Wednesday, January 5, 2011

Internal Voltage Divider Done - now get 1V/Oct

Here's a solution to get 1V/Oct - I just used a trimmer as a variable voltage divider to replace the external test V-divider I made before. I'm still tuning it right now, and the sweet spot drives the octave range up two full octaves (So note C3 = C5).

More spaghetti!

So (for novices like myself) I took CV in to pin 1 (could have gone to pin 3, opposite operation), the line the R7-south off pin 2 (the wiper) and a wire to ground from pin 3 (could have used pin 1, opposite operation).
Still, could have saved all the trouble with Silent Way!

Febuary 6th 2011 - Additional Info:
Here's the basic circuit for the voltage divider:

Instead of using two resistors for a fixed voltage divider, a single trim pot replaces both.
Then terminal 1 (or terminal 3) is equivalent to the Vin connection above. This will be the CV input.
Then terminal 3 (or terminal 1) goes to ground.
Then terminal 2 on the potentiometer (trim pot), which is the "wiper" terminal, is Vout above. This will go to south side of R7 if you did Din Sync's mod for CV input.
The interchanging of terminals 1 and 3 does not matter; the direction of operation will just be opposite for either choice - resulting in Clockwise (CW) operation or Counter-CW operation.
This circuit is based on the ratio of Z1 and Z2 (or R1 and R2 for resistors). Because of this, using two 10k resistors is identical to using two 100k or two 1M resistors, according to the following equation:

Vout = [R2/(R1+R2)]Vin
For the list of values above you will always get that Vout = (0.5)Vin.
With a trim pot you can "tune-in" the right ratio to get Gakken on 1V/Oct.

Note that this is the simplest case. To get proper V-division, you would have to know about the impedences of the circuitry connected to it.

Etched PCB for monotron - remote knobs

Here's some pic's of chemical etching in progress. I wanted to keep original knobs from a second monotron - to build a dual VCO monotron using two monotrons - so had to make remote board for surface mount knobs.

Etching off the copper

After a few minutes agitating the board

Was taking longer than expected, apparently chemical reacted with tin coating on paint tray...
Thats why it was getting warm!

New tray - ceramic baby

Almost done - and no skin burned off.

Only the etch-resist remains.

Nice. Rough, but it works.

All of this was also a test run for the squarewave/PWM mod, similar to the Gakken mod, except that the monotron one I found requires a PCB. I've been drilling holes (with a hand drill) and rubbing on etch-resist dots for a while now:

Lots of dots..................

Will put up links and such as project progresses. Next I have to paste on the lines.
So far I've stripped all knobs and jacks off of the second monotron and today I ripped apart the power supply, as I want to feed everything from first unit (if it works???).