Boss CE-2 chorus pedal schematic

The Boss CE-2 is a great analog chorus pedal from the late 70s and early 80s. According to this page on BossArea.com, the marketing of the CE-2 was stopped in November 1982, but the pedal was still produced and sold at least until 1990. Even though it's no longer in production there are thousands of these pedals being used by guitarists all over the world -- it's one of the more sought after Boss pedals on the used market.

Fig. 1: Boss CE-2 chorus guitar pedal schematic diagram

Fig. 2: Boss CE-2 chorus board - front and back

Specifications:

- 2 Control Knobs: Rate and Depth
- Connectors: Input, Output, AC Adaptor
- Input Impedance: 470kOhm
- Signal/Noise Ratio: more than 90dB (IHF-A)
- Output Load Impedance: over 10kOhm
- Maximum Allowable input: 0dBm(100Hz), -10dBm(1kHz)
- Recommended AC Adaptor: ACA Series
- Current Draw: 9 mA (DC 9V)
- Weight: 400 grams (0.88 lbs.)
- Dimensions(mm): 70(W) x 55(H) x 125(D)

The circuit is designed around the MN3007 1024 stage BBD (IC3) and the MN3101 clock driver (IC4). The input and output circuits use a uPC4558C IC while the LFO is made with the help of a TL022LP op-amp IC.

Other active components:

D1, D2, D4, D5 and D8: 1S2473 or 1S1588 (switching diodes)
D3: 1S2473 (replaced with a wire jumper in newer models)
D6: RD5.1EB (5.1V Zener diode)
D7: RD11EB (11V Zener diode)
Q1-Q3: 2SC732TM-GR (NPN silicon transistors)
Q4-Q8: 2SC945-P (NPN silicon transistors)
Q9: 2SK30A-Y (Silicon N-channel junction field effect transistor)
LED diode: SLP-135B

Adjustment procedure:
Turn the Rate knob fully counterclockwise (min.) and the Depth knob fully clockwise (max.). Feed a 200Hz, +3dBm sine signal into the input. Connect an oscilloscope to the emitter of Q3 and turn VR3 until you'll get a centered operating point (a symmetrical sine wave, equally clipped at top and bottom).