Buchla 261e - notes

Revisiting the Buchla 200e.
I'm slowly working my way through the 200e manuals and re-writing my notes.
I'll update this as I go along.
This post is mostly about the 261e, however I can't help to notice its similarities with the old 259

Of course the 261e is just 1U ...Don has packed a lot into a small package.
Both have modulation & principal Oscillators.
In the 261e, the oscillator core is now a digital sine wave.
I understand that the 259 had a triangle core (analog of course).
For more about oscillator cores read here

 

Modulation Oscillator:

The modulation oscillator on the 261e can be switched between 3 settings: Low, Hi & track
In "Low" or sub audio mode it oscillates between 0.25 Hz and 64 Hz.
In "Hi" or audio mode it covers a frequency range between 27 Hz and 7040 Hz.
In "Track", it follows the pitch of the main oscillator and can be shifted relative to it regarding pitch.
The offset will be zero when the modulation frequency is set to 440 Hz. (indicated by extinguishing the bicolor LED).

An F.M. input for the Modulation Oscillator provides for frequency modulation.
The waveshape of the MO is voltage controllable. This ranges from sine through square and pulse;.
There is also a multiplying input (the centre banana in the above picture). This varies the degree and direction of waveshaping.

The output of the modulation osc is internally connected to the the principal oscillator
The Amplitude (AM), Timbre & Pitch (linear FM or frequency modulation) of the Principal Oscillator are the main targets.

You can apply this modulation either singly or in combination.

Under Amplitude, there is a point where it acts like a ring modulator.

The Timbre section has 3 parameters: Timbre, Symmetry (direction) & High Order (magnitude).
Symmetry and high order have variable offset and are voltage controllable.

If all the pots are set to zero, the output wave shape will be a sine.
1. The Timbre (Top left knob) knob adds harmonics as you increase the value.
    It's the wavefolder
2. Symmetry controls how different one half of the waveform is from the other.
    As you turn it from zero, it will change the sine wave to a square wave.
3. High Order acts a little like a high pass filter.
    As you turn it from zero, it will change the sine wave to a spike wave.

Note that pitch modulation responds only to sinewaves.

Sync Facility of MO
This permits synchronization of the Modulation Osc to MIDI note-on messages, or to subdivisions of the principal oscillator.

Hard sync truncates the waveform; soft sync uses a phase locked loop to achieve synchronization.

 

Principle Oscillator

 The core is a digital sine wave.
 The frequency ranges from 27 to 7040 Hz,

There are attenuators  and jacks for both the pitch CV (banana) and the audio-FM input.
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Internal Buss settings for the 261e & a 225e preset manager.

Bus I.D. for the module is set with two board mounted switches IN THE LOWER left corner

The module ID can be displayed on the 225e preset manager by holding the remote enable switch on the 261e for about two seconds. 

You should see something like this:
Here, the 261e is on Buss C.

The normal settings start at A and go for as many modules as you have (up to D, or four).
The 261e responds to pitch & fine tune messages via the 225e.

 MIDI Fine tuning

To respond to MIDI fine tuning messages, the “Ft” field in the 225e’s display must contain something other than a default value of “An” for the bus of interest (buses A – D).
The fine tune data is in cents (a cent is 1% of a semi-tone), and can range from –49 cents to +49 cents. It can be set for each bus, and therefore for each of four oscillators.

Note that if fine tuning is enabled for a particular VCO that oscillator’s pitch knob will be incapacitated, as will its F.M. input and control voltage input. Pitch will be completely determined by MIDI signals.
So if you want to use the VCO knobs as normal, keep the setting on "An".
"An" I believe stands for analog

To be continued.................