Saturday, February 17, 2007

MC-7 keyboard

I found a nice keyboard from flea market yesterday. It was not in very good condition-> the drum section was completely silent. I opened it and found that some components were loose because of bad soldering work. After soldering these properly the drums started working.
The sounds of this keyboard are simple but very nice. All keyboard instruments are quite raw sounding squarewave. Drum sounds are short noise (hi-hat), smooth click (bass drum), and sharper click (snare).

Original features:
2 notes polyphony (monophonic if accompaniments are on)

Cotrol panel from left to right:

-power on/off switch
-accomp volume 4 way switch – this controls only volume of the drums not the accompaniment bass line
-master volume 4 way switch

Rhythm section:
-8 preset rhythms: disco, march, rock, waltz, pops, 16 beat, rhumba, bossanova
-accomp on/off button: the accompaniments are very simple and funny
-tempo buttons: slow and fast
-synchro button
-start button
-stop button

Orchestra section:
-8 preset instruments: clarinet, violin, oboe, piano, elec guitar, xylophone, harpsichord, mandolin
-sustain button
-vibrato button
-demo button

record section:
-record button: 28 notes
-play/stop button

Custom drummer section:
-3 drum pads: bass drum, snare, hi-hat
-program button: 16 steps
-play/space button

After some testing I found out that each of the three drum sounds are triggered from individual pins from the ic. There is also a fourth trigger pulse witch was unused in this model. I soldered wires from all 4 pins. Now I have 4 trigger output lines that follow the preset rhythms and three of them (bass drum, hi-hat and snare trigger signals) are programmable for 16 step sequences. These wires can be connected to various points on the pcb, when 1 or more of them are routed to the pins that read the buttons/keyboard you get many strange rhythmical bleeps and other crazy features like “bouncing” tempo and “random” notes and chords played.
I also found the output pins for keyboard sounds and the accompaniment sounds, these can be connected to various points on the pcb to change and modulate the sounds in many ways.Because the many possibilities of expanding the features of this keyboard I decided to build an extension case to fit the new controls, outputs, patch bay etc. So many ideas: adding a low pass filter circuit, new drum sound circuits to use with the trigger signals, joystick controller for some features, new buttons, switches and a patch bay…. a lot of decisions to make.

Well now I addad few wires (30 and counting) to different points on the pcb. All of these will be going to a patch bay so there is quite many possibilities to change the sounds and functions of the keyboard. Here is a picture.

The new wires from the pcb are soldered to a piece of stripboard so it will be easier to direct them to different controls and patch bay.

After some thinking and going through materials at our studio. I found the perfect extension case. It seems that I´m going for a modular design with this one. :)

Here is mc-7 posing with the extension case. I cut some new panels from red plastic. The alumnium panels were on the case.