251e Quad Sequential Voltage Source
Four independent sequencers, each with a pulse output and control voltage output for each of 50 stages. A separate editing section provides for setting each parameter for a selected sequence; the sequence may proceed while editing a particular stage, or the edit section can track the sequencer, displaying parameters in real time, but disabling edit procedures.
Editing a sequence
To edit a particular sequence, press the sequencer's blue "display/edit" button. The associated LED will ignite, and the stage number it is currently on will appear in the "STAGE EDIT" section. Use "stage #" to select a stage for editing. A press of the currently selected "display/edit" switch will terminate the editing mode, the blue LED will commence blinking, and the edit section will display in real time the current parameters as the sequence progresses. Editing is not possible when in this mode.
The parameters in the first edit section, "SEQ. EDIT" affect 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).
When a number between 6 bpm and 300 bpm appears in the "tempo" field (the usual case), each sequence operates as follows:
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; 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. If a sequencer has a blank in its initial delay field, then the start pulse merely starts the sequence at the current stage number. A toggle switch performs the same function from the front panel, alternating between green and red LED's, which display the current sequencer mode. When a stop pulse is received, the sequence is stopped.
Other modes besides the internal clock may 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:
b A - "stop" pulses decrement (back) 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" 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 (retrograde) order. Reverse and sync interact peculiarly. Use them simultaneously at your own risk.
"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 "copy" again to complete the copy process.
Similarly for "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. All parameters will be reset to their default values.
To end a sequence, use the yellow button to 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.
To use a sequence as a master for the following sequence, set one (or more) "sync next" pulses in the stage(s) you would like the next sequence to start on. Sequence A can thus sync sequence B, and so on, with stage D wrapping around to sync stage A. Synced sequences do honor the initial delay.
Editing the Stages of a Sequence251/2
In the "STAGE EDIT" section, we set the parameters for individual stages.
First is the interval, entered as a note value from 1/64 to a whole note (1/1). If desired push the button until the 1.5 LED is lit and the displayed note will be dotted (interval multiplied by 1.5). Or push the button again to illuminate "triplt", causing the interval to assume the time value of a triplet note (interval multiplied by 2/3). If the knob is pressed, a zero interval will be entered, indicating that the stage will be skipped; pressing it again will restore the original interval.
The next display sets the voltage value for the stage, variable from 0.0 to 10 volts, conveniently accommodating oscillators with sensitivity of 1.2 volts per octave. (Each .1 volts adds 1 semitone.)
To achieve a finer control of the 251e's output voltages, you can set the cents offset from 00 to 99 cents for each stage. This is accomplished be pushing the voltage adjustment knob. The display will blink, reminding you that you are setting the number of millivolts to be added to a stage's output. (A millivolt, if directed to an oscillator with 1.2 volts per octave pitch sensitivity will alter the oscillators pitch by one cent – 1/100 of a half tone.) Push the adjustment knob again to return to the display of volts. The right decimal point ignites if the output contains a non-zero cents field.
The next parameter is duration, which determines how long the output pulse lasts, as a proportion of the interval. The choices here are trans, ¼, ½, ¾, and x1, all representing fractions of the total interval. "trans" selects a pulse with no duration, triggering an attack with no sustain. Durations of ¼ and ¾ occur when two adjacent LED's are illuminated. When all LED's are off, no pulse appears at the output for the stage being edited.
The next parameter is a loop counter; the LED indicates the first stage in a loop; the numeric 1-9 indicates the last stage as well as the number of loops executed before proceeding to the next stage. In operation, the sequence proceeds until a number is encountered, then jumps back to the first "beg" it encounters. The loop count is decremented each repetition, and on reaching 0, the sequence proceeds and the loop counter is reset to its original value. If the loop number has been set to A, the looping will continue Always, requiring a start pulse to extract you from the infinite loop. Note that if the sequence is running in the reverse mode, the roles of the loop number and the begin stage are reversed.
An additional complexity is the looping of begin points; if a number is inserted in a stage designated as a begin point, then the begin will be honored for that number of loops. When the number is reached, the sequence will jump back to the next loop point, resetting the loop counter to its original value.
The last parameter is the stage number, which is used to select the stage for which information is displayed and edited.
The 251e has the capability of copying information from one stage to other stages. To perform this trick, hit the copy button so its LED is blinking. Now, instead of hitting the "display" button, as we did for copying sequences, hit the switches or turn the knobs associated with the parameters you'd like to copy; the LED's (or displays) will proceed to blink. Turn the stage number pot to each of the stages you'd like to copy to, depressing it to activate the stage copy. You may hold it depressed while turning it to address contiguous stages. Complete the operation by pressing "copy" again. Note that when copying a duration value of zero, all three LED's will blink, and when copying a stage that is neither dotted or a triplet, both LED's blink, reminding you that this parameter is both zero and primed for copying.
The Master Clock
All sequencers are driven from a "MASTER CLOCK". When the bicolor LED is off, displaying neither red nor green, the master clock multiplier is exactly 1, and the tempos for the sequencers will be precisely as indicated. Turning the knob or applying a c.v. to this section will advance or retard this clock, with the maximum advance equal to 1.5 x the indicated tempo and the maximum retardation equal to . 5 x the indicated tempo.
All parameters of the 251e can be stored and retrieved as part of a preset. The remote enable light must be on to accomplish this, and either a 225e or 206e preset manager must be present in the system.