Monday 15 April 2019

Buchla 251e - my notes

These are my user notes for the Buchla 251e.

The top half of the module contains 4 independent 50 step sequencers and their programmable control voltage inputs and output jacks.
Each stage has it's own pulse output and control voltage output for each of 99 stages.
Each stage is truly independent from the others... they can have their own tempos, time scales, pulse durations, stage lengths, etc.

Incoming “start” and “stop” pulses control each sequencer’s progress.
A “stop” pulse stops the sequence at the current stage number.
A “start” pulse does one of two things:
1. if there is a value entered for the initial delay, it resets the sequence to stage 1, and starts the sequence after the delay time has expired.
2. If a sequencer has a blank in its initial delay field, then the start pulse merely starts the sequence at the current stage number.

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SEQ Edit & STAGE Edit
The middle section has a sequencer edit interface and the stage edit interface.
This editing section allows you to set each parameter for a selected sequence.
The sequence can be running while editing a particular stage.
Also, the edit section can track the sequencer, (displaying parameters in real time),
but disabling any editing.


Sequencer edit section:
This manages the general relationships between the 4 sequencers such as copying, syncing, and pasting.
It affects the entire sequence, and not individual stages. (exceptions – “end” & “cycle” are displayed only for the last stage of a sequence, and “sync next” causes the following sequencer to reset to stage 1 whenever it is encountered).
It also manages the settings of each specific sequencer.... things like length, tempo,  cycling,  and the reversing of each sequence.

Tempo 
The internal clock has a range from 10bpm to 300bpm is supported.
Other modes besides the internal clock may also be used to advance sequences or select their stage numbers. Push the tempo knob to advance through five alternative schemes, all of which assign
new and novel functions to the “stop” and “start” pulses:

d A - “stop” pulses decrement the stage number; “start” pulses Advance it.
J A - on receipt of a “stop” pulse, the stage number Jumps to the
         next stage number that contains a “loop begin”; otherwise it jumps
         to stage 00. “start” pulses Advance it.
S H - “start” pulses sample the control voltage applied to the “stop” pulse;
          The sampled control voltage is applied to stage selection.
d i r - a control voltage applied to the “stop” pulse is directly applied to stage
          selection. A ”start” pulse inhibits this activity.
c l o - “start” and “stop” pulses are ignored. MIDI clock is enabled.

 init delay
“init delay” delays the sequencer start whenever it receives a start pulse.
It does not affect the timing otherwise, being ignored when cycling or looping.
The delay is in hundredths of a second, yielding a range from .01 to .99 sec. (Imagine the decimal point).
If nothing is entered in the initial delay (display is dashes), then the start pulse advances the sequence without resetting it.

“reverse” plays the sequence in reverse order.

“copy” copies the displayed sequence. With the copy LED on, hit the display/edit button for the sequence that you would like to copy the current sequence to. The copy LED blinks, and the edit section displays the sequence being copied to. Hit the copy button again to complete the copy process.

"clear" .....With “clear” illuminated, hit the display/edit button for the sequence to be deleted. The “clear” LED blinks; hit it again to complete the transaction.

"end" ................To end a sequence set an “end” in the stage you’d like to be the last. If desired to repeat the sequence, set “cycle”. Remember that in the cycle mode, “init delay” is ignored.
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Stage Edit:
This manages each individual step.
To edit a particular sequencer's setting, press the blue "display/edit" button specific to the sequencer in question.
 The associated LED will ignite, and the stage number it is currently on
will appear in the “STAGE EDIT” section.

Solid blue light = edit mode.
Blinking light = run mode (no editing is available)

In edit mode you can select the stage number and its companion CV value.

The CV voltage (on the indicated blue knob) range is 0V to 9.9V.
You can press this knob the display will blink .... this tells you that you are in fine tuning mode.
pressing the knob again will return you to coarse tuning mode.
0.1V = 1 semitone in pitch.



The 1/interval knob selects the denominator for note sub divisions.
1/1 = a whole note
1/4 = a quarter note
etc etc

Turning this knob to the right increases the value from 1 to 64. (single digits only).
If you turn the knob to the left, the values jump (they double) 
between the whole digits :  1, 2, 4, 8, 16, 32, 64.
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There is a yellow & green button to the extreme left.

The lower left green button sets the pulse duration outputted for the selected stage 
(the length of the stage itself is set with the "interval" control). .
Pulse durations may be set to fractions of the intervals. 
Press "dur" to cycle thru the LEDs. "x1" gives a pulse out for the length of the stage. "x1/2" gives a pulse out for half the length of the stage. "trans." gives just a short transient pulse at the beginning of the stage. If no LED is lit, no pulse is generated for this stage.  

The upper left yellow button sets triplets and dotted notes. 

 
 

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 Loop beginning & ending points are programmed here.
The Master Clock.

When the bicolor LED is off, displaying neither red nor green, the master clock multiplier is exactly 1,
Turning the knob or applying a c.v. to this section will advance or retard this clock.
Max advance = tempo x 1.5
Max retarding = tempo x 0.5

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Additional features include:
Inter-sequencer triggering
Variable start delay
Retrograde capability
Multiple nested loops
Master voltage-controlled clock

With the 206e or 225e Preset Manager, the parameters of the 251e can
be stored and retrieved as part of a preset.
A 200e USB card is necessary to download new firmware for this module.

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