#37-key import keyboard mods

1 messages · Page 1 of 1 (latest)

hallow elbow
#

This thread is to document my work done on a brandless 37-key electronic keyboard. Pictured is the box and both halves of the case, front and back.

IMG_5936.jpg IMG_5934.jpg IMG_5933.jpg
#

Visible in this picture is an existing mod of mine replacing a 2.2 kOhm clock resistor with a pot going to the front panel. One of my first work items was reversing this, because the clock circuit didn’t seem to like having such long wires

#

I have since replaced the flying leads pot with a 10 kOhm trim in series with 220 Ohms

IMG_5937.jpg
#

And then melted a hole in the back of the case making the tune pot trimmer accessible

#

The degree to which this thing is hand-built is a little unnerving. Six PCBs and maybe a dozen flying wires

#

I’ve reverse engineered the boards 80% of the way, obviously I can’t do anything with the COB but it’s quite funny that the keyswitches aren’t matrixed. The front panel is

hallow elbow
#

haven’t fully TRACEd the power amp board but it’s a cute 2 transistor thing

#

the keyboard does a funny thing when you exceed a certain tuning frequency where the key matrix ceases to scan properly

#

it also has a really awesome voltage sag

#

I haven’t finished tracing out where the various colored wired exactly go to … I have vague ideas based on how the blocks function

#

this keyboard is more spartan than you can believe; single layer everywhere; scratchy switches for volume; mono out jack

#

roughly, the mic and volume sliders switch resistors in series with the mic jack and chip output

#

the left transistor does all the summing, the right transistor is the power amp

#

it really does seem like there’s only the local feedback bias on each stage but the unpopulated RC maybe ought to come from the right collector

#

the pot makes all the difference with the usability of the drum section — more of a drone section now. Perhaps later I will still add vactrol clock control. Would be very cool to CV.

#

the more i play with it the more I realize I like it how it is though. tweaks and reinforcements for now

#

you could conceivably tear the chip and key matrix out of any toy keyboard w drummer and get a decent practice trainer out of it

#

make a replacement key matrix for the rhythm section with fake cherry switches, 3D print a case, sell on reverb for $1,700

#

oh shit

#

ah

#

wow this is a fantastic resource

#

so I can certainly have separate outputs and/or balance for the rhythm and voices

#

as a "joke" someone should take the guts out of one of these toy keyboards and stuff it into a well-built walnut synth cabinet with an organ keybed and really chunky radio switches

#

conceivably an organ keybed could actuate multiple such keyboards, a chimaera beast instrument

#

well, a key matrix diodes would be a good next thing to do

#

seems like I just cut a trace in series with every switch and solder a diode in place

ruby sky
#

Thinking about it it indeed seems like a fun thing to bend

hallow elbow
#

oh shit!

hallow elbow
ruby sky
#

Yeah indeed, quite funky

hallow elbow
cosmic sigil
#

You had the same toy keyboard, but it's actually different?

cosmic sigil
# hallow elbow

So the right one is the power amp you say? Where does green go?