October 23, 2008

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....

6 comments:

Mike said...

I'll say it again: wonderful service you're providing here. I've been fascinated with his way of doing things since first reading an interview with Buchla reprinted in the copy of Tom Darter's 'Art of Electronic Music' in my high school library, around 1991...

Recently, I was one of the lucky ones that scored a copy of the Easel manual in that eBay auction, and that's gone a long way towards clearing things up... your blog is doing much more than making up the difference.

Again, thanks- wonderful work you're doing here.

Mike said...

Also, while we're playing 'what-if...'

That 208 Timbre control? Okay, apply that to the sine fundamental coming out of a 148. Only it's a 148 that maybe goes beyond 10 harmonics, and maybe the harmonics can be detuned (because we don't want horrible Hammond-style ET or simple whole-integer harmonics-just a few cents either way would make a big difference).

Now, wouldn't that be lovely? Programmable harmonics with adjustable tunings and levels, the coolness of the Timbre folder, either/or, and then a CV could sweep between the two.

Benjamin said...

If you reissued the Music Easel I'd buy one. :-)

Quad said...

Cloning this oscillator would definitely be an interesting project, i'd like a couple of boards for sure!

Reed said...

Mike, doesn't the 148 make its harmonics with wave-folding in the first place?

mark verbos said...

The 148 makes the odd harmonics using a circuit that folds a triangle wave much like the circuit in the 259 or 208. It's not a circuit that you just send in a sine wave and get out all the harmonics though. It doubles the triangles using a full wave rectifier and multiplies by 3, 5 , 7 and 9 using wave folders. Then converts all of those to sines individually.