CP-251
TECHNICAL INFORMATION
This section contains technically-oriented information which is somewhat more
detailed than the previous sections . Some users will find this information helpful in
devising advanced uses for the CP251. The information is arranged according to the
CP251 module to which it applies.
MIXER
The nominal input resistance of inputs #1 and #2 is 50KW. The nominal input resistance
of inputs #3 and #4 is 100KW. The nominal output (source) resistance of each of the
outputs is 500 W.
The maximum input-to-ouput gain is unity. The maximum nominal output voltage range
is ±5 volts. The - output is the negative of the + output.
The frequency response of the mixer is DC to 50kHz.
The OFFSET knob can be considered a fifth input with a voltage range of ± 5 volts.
LAG
The nominal input resistance is 10 megW. The nominal output (source) resistance is
500 W.
The nominal input-to-output voltage gain is unity.
Time constants of rising and falling waveform edges are determined by the RISE and
FALL knobs. Nominal time constants are 1 millisecond, 100 milliseconds, and 1 second
when the knobs are fully counterclockwise, in midposition, and fully clockwise,
respectively.
LFO
The nominal input resistance of the PEDAL IN jack is 120 kW. The nominal voltage-tofrequency
characteristic of this input is: a one-volt increase doubles the frequency.
The operating frequency of the LFO is determined by the sum of the voltage at the
PEDAL IN jack and the voltage coming from the RATE control. An expression pedal such
as the moogerfooger EP-1 has a nominal range of 0 to +5 volts when plugged into the
PEDAL IN jack. You should use the RATE control to set the minimum desired LFO
frequency, and adjust the voltage range of the pedal or externally-applied control
voltage to get the desired range of LFO frequencies.
The LFO frequency can go both lower than the minimum calibration on the RATE
control (by applying a negative control voltage), and higher than the maximum
calibration on the RATE control (by applying the appropriate positive control voltage).
The minimum frequency is less than 0.03 Hz (one cycle every 33 seconds), and the maximum frequency is greater than 100 Hz.
The nominal peak voltage of the triangular and square waveforms is ±2.5 volts . The
nominal output (source) resistance of each of these outputs is 500 W.
ATTENUATORS
Each of the attenuators is a 50KW, linear taper potentiometer. The IN jack is
connected across the potentiometer element, while the OUT jack is connected from
the counterclockwise end of the element, to the potentiometer’s wiper arm.
FOUR WAY MULTIPLE
The tip terminals of all four jacks are connected together. The sleeve terminals of all
four jacks are connected together.
NOISE
Nominal peak output voltage is ±0.6 volts. Nominal RMS output voltage is 0.17 volts (-
13 dBm).
Nominal output (source) resistance is 500 W.
Frequency band of the noise waveform is 500 Hz - 3,500 Hz.
SAMPLE AND HOLD
Nominal input resistance at the IN jack is 10KW. Nominal voltage range which this
input will sample is ±3 volts.
Nominal input resistance at the TRIG jack is 10KW. Triggering occurs when the voltage
at the TRIG jack descends through the +1 volt nominal trigger threshold.
Nominal input-to-output gain is unity. If the noise source is sampled, then the output
waveform appearing at OUT 1 is about ±2 volts peak-to-peak. In between samples, the
maximum output voltage drift rate is no more than 0.1 millivolt per second.
The nominal input-to-output gain from the IN jack to the OUT 2 jack is X2. A two-pole
direct-coupled lowpass filter is placed between OUT 1 and OUT 2. The cutoff frequency
of this filter is proportional to the LFO frequency. Thus it is possible to voltage-control this
filter, and to set its cutoff frequency to as low as a small fraction of 1 Hz.
RED JACKS
The CP251 contains a total of eight jacks with red nuts. The Ring terminal of each of
these jacks is supplied with +5.6 volts at a nominal maximum current of 600
microamperes. This is more than adequate to supply operating current to normal
expression pedals. Electronically-inclined users are encouraged to experiment with novel control devices that are powered by the CP251’s red jacks (as well as by any of
the pedal/control jacks on moogerfooger MF-Series products).
Plugging a conventional two-circuit phone plug (tip-sleeve) into any of the red jacks
will not adversely affect the operation of any part of the CP251. Such a phone plug will
short that jack’s pedal supply to ground, causing a current of about 2 milliamperes to
flow through the plug’s barrel.