CP3 Mixer

Faithful recreation of classic CP3 Mixer in MOTM format with “signal present” and “clipping” LED indicators. The latter is very useful when you want to set levels so that clipping occurs only when slightly detuned waves are in phase and reach maximum amplitude, resulting in a very nice PWM-like sound with lots of movement. It also comes handy when you want to avoid clipping and use CP3 as a regular linear mixer.

CP3Mixer#2_small  CP3Mixer#3_small

Technical characteristics

  • 3 x inputs with level knobs
  • 1 x output with level knob and polarity selector switch
  • Power supply: +-15V
  • Power supply current: +50mA/-30mA
  • Gain from 1.1 to 5.6, set by on-board trimmer

PCB

cp3mixer_pcb

CP3Mixer_PCBs_small

DIY Resources

Bill of Materials

Schematics: cp3mixer#1 cp3mixer#2

Front panel: cp3mixer_panel (Front Panel Express file)

Calibration

  1. Turn all input pots to min position and use BALANCE trimmer R9 to get positive output DC offset as close to zero as possible. Typical offset values are less than 10mV.
  2. Connect 10Vpp signal to input 1, set its level control to 12 o’clock, set other input level controls to min position, and output level control to max position. Use GAIN trimmer R11 to set output to 10Vpp (unity gain).
  3. Set low level trimmer R24 so that voltage at pin 2 of IC4 reads 250mV. At this setting green LED will light up when output voltage is about 1Vpp.
  4. Set high level trimmer R26 so that voltage at pin 6 of IC4 reads 10V. At this setting red LED will light up when output signal is about to get clipped.

Ordering

To order CP3 Mixer PCB, please send an email to pete at kvitek c o m specifying how many PCBs you need, a country where to ship them, and an email address to send the PayPal invoice to.

Prices (US dollars):

  • CP3Mixer PCB — $20

California residents add 8.75% tax

Shipping:

  • Continental USA — $5
  • Canada – $10
  • Europe, Asia and Australia  – $15

Please make sure your PayPal shipping address is correct!