Tuesday, March 26, 2013

I found an Optigan!

This past weekend, I found something from my musical "Holy Grail" list....an Optigan! The Optigan was built in the 1970's by Mattel Corp. (yes, that Mattel) in Compton, California (yes, that Compton). Wikipedia has a pretty good overview : http://en.wikipedia.org/wiki/Optigan The Optigan used samples recorded on circular film stock that looks like a vinyl LP, but you can see through it. Each key on the keyboard was mapped to a separate track on the optical disk. There were also tracks for the chord buttons and 5 special effects buttons. The Optigan was built by a toy company, thus the dodgy build quality. Some internal parts would disintegrate, the rubber idler wheel would get hard and the disk would slip. Nonetheless, the Optigan and its' low-tech sampling capablity has appeared in many commercial recordings (and still does to this day...check out the Optigan Facebook page). My main interest is historical. Here is my Picasa album of the teardown. When I brought it home and plugged it in, for the most part, it worked (this is unusual for Optigans). The special effects buttons were intermittent so I had to take off the top to access the buttons. To remove the top, the sides must be removed because they cover the screws that hold down the top. Yay. The pictures show the state of the internals. Not so bad. While reassembling, a small wire which moves the disk assembly fell out. In order to reinstall the part, I had to pry out an internal panel, replace the part (with forceps) and screw it back together. Another common problem is the idler wheel. The rubber has turned hard and slips on the disk. It can be resurfaced, but requires major disassembly to remove the part. Once I have a service manual (or at least a procedure), I may attempt this.

Thursday, March 07, 2013

Raspberry Pi, Puredata and MIDI

My initial test with the Raspberry Pi running Puredata did not go as well as I had hoped. Noticeable noise in the output audio. In my MUS306 class today, MIDI was the topic of discussion. Why not MIDI? Connected my $5 no name MIDI interface to the Pi and started Puredata. Changed the configuration to turn off the audio output and set the MIDI ports. Used my Yamaha QY-10 as the MIDI tone generator. Everything worked perfectly. Now I'd like to see if I can attach controls directly to the GPIO port. This would save me from having to attach another MIDI device.

Hammond Tone Generator - Part 3 - FInding the usable tonewheels

I have tested the outputs of the tone generator...there will be about 60 usable outputs. The other 31 outputs consist of the lower frequencies..the windings on the tonewheel cores include resistance wire which drops the levels significantly. I will have to further dismantle the TG to see if the resistance wire can be bypassed. I don't think that further dismantling is worth the potential of damaging the TG. I know that at least 2 or 3 of the tonewheels are stuck and will be looking at those to see if I can get them working. Fortunately, there appears to be a correlation between the color of the wire from the tonewheel and whether I am seeing usable output. For example, none of the red wires produce usable output. Most of the orange wires provide usable output. If I'm not getting output from an orange wire, something is probably stuck or broken. I have documented all the wire colors and whether I am seeing output. Next step is to recheck the outputs that should be working.