Prototype Music Easel!?

The Music Easel is the street name for the combination of the Buchla 208 and 218 touchplate keyboard. I was recently called upon to repair the prototype unit, built in 1973. This unit was resurrected in 1987 and had since been in a basement, used from time to time without ever being moved. He built a very cool blue wood enclosure for it with a built in linear power supply.

When it changed hands, several problems appeared. The 208 module is built from a large motherboard with 12 perpendicular daughter cards, attached with .156" Molex connectors. The biggest problem was that the connectors had oxidized and the cards had to be jiggled around to get several of them to work. The 20 years that this thing sat in the same spot it was fine, but I guess shipping did a number on them. I replaced the female side on all 12 cards and things started to get better.


The Oscillator and some other parts were still not working properly, so I set out to find the problems. Being the prototype, there are several things that are not the same as other units. The panel has a sine wave in the modulation oscillator, when it actually puts out a triangle, the memory card edgecard connector is smaller, the Envelope and Pulser sliders are labeled backwards and the modulation oscillator's banana output jack covers some text. The boards are filled with cut traces and flying resistors. It was a lot of fun.


Finally, I got to the 218. It was only triggering notes while you touched one of the grounded frets. The original owner thought this was normal, but I have used these before so I had to figure out what was wrong. I found that the resistors controlling the keyboard signal's gain were different on the schematic, the parts overlay AND the picture that I had taken of a working unit when I serviced it. I tweaked these values until the keys triggered normally.

Music Easel Oscillator

The oscillator section in the 208 module can be seen as a rest stop on the way between the 258 and the 259. The "timbre" section is introduced as well as a switch to select waveforms. It's the first time Don implemented a dedicated modulation oscillator and trimmed keyboard CV inputs.

Interestingly, the original version of the 208 used a totally different design than the 258 or the 259, with Vactrols in the oscillator core. I don't know how many of these were made, but it was fazed out in favor of the 259-like design you can find schematics for on the web.

The "Timbre" control introduces wave folding on the sine wave, but does not effect the other waveforms at all. There is a separate, unlabeled knob above the waveshape switch that controls the mix between sine and the other shapes. The wave folder's effect disappears at the full CW position of this control.

I built a clone of this oscillator about 6 years ago, using 2 single sided photo etched boards. I modded a few things to make more sense in a dedicated module. There are a few lessons I learned, that I would do differently, if i did it again. It is a nice design and I think it has validity, even alongside other Buchla oscillators.



Going through my box of abandoned old PCBs, I got the idea that maybe this would be a cool module to throw together, considering the hype surrounding the Music Easel. Maybe it's time to revisit this one....