Boss CE-2B Bass Chorus pedal schematic
This old Boss CE-2B Bass chorus generates a very clean and transparent sound. It has almost the same circuit as the CE-2, with only a few differences. The most significant difference is the additional knob (E. LEVEL) to control the blend of the direct and processed signal.
Fig. 1: Boss CE-2B Bass Chorus guitar pedal schematic diagram
| Differences between CE-2 and CE-2B: | ||
|---|---|---|
| Symbol | CE-2 | CE-2B |
| VR4 | - | 250KC (E.LEVEL pot.) |
| C14 | 33nF | 12nF |
| C26 | 470pF | 220pF |
| C27 | 470pF | 220pF |
| R53 | 100Ω | 390Ω |
| R42 | 1kΩ | 100Ω |
| D6 | RD5.1EB (5.1V Zener) | RD5.6EB3 (5.6V Zener) |
| D7 | RD11EB (11V Zener) | S5500G (400V/1A diode) |
| Q1-Q3 | 2SC732TM-GR | 2SC2240GR |
| LED | SLP-135B | LN-28RP |
Specifications:
- 3 control knobs: Rate, Depth and E.Level
- Connectors: Input, Output, AC Adaptor
- Signal/Noise Ratio: more than 90dB (IHF-A)
- Residual noise: less than -100dBm (IHF-A)
- Input impedance: 470 kOhm
- Output load impedance: more than 10 kOhm
- Maximum input level: 0dBm (100Hz)
- Recommended AC adaptor: ACA Series
- Current draw: 10mA (DC 9V)
- Weight: 400g
- Dimensions(mm): 70(W) x 55(H) x 125(D)
- Dimensions(inches): 2-3/4(W) x 2-1/4(H) x 5(D)
ICs, transistors and diodes used in the Boss CE-2B bass chorus:
IC1: NJM4558DD (dual operational amplifier)
IC2: TL022CP (dual operational amplifier)
IC3: MN3007 (1024 stage BBD)
IC4: MN3101 (BBD driver)
Q1-Q3: 2SC2240GR (NPN silicon transistors)
Q4-Q8: 2SC945P (NPN silicon transistors)
Q9: 2SK30A-Y (Silicon N-channel junction field effect transistor)
D1, D2, D4, D5 and D8: 1S2473 (switching diodes)
D6: RD5.6EB3 (5.6V Zener diode)
D7: S5500G (400V/1A rectifier diode)
LED diode: LN-28RP
CE-2/CE-2B differences
The CE-2B circuit is almost identical to the CE-2 with only a few differences. The most obvious change is the additional 250kΩ E.Level potentiometer inserted in series with R22 (47kΩ). Also, a component of the high-pass filter, the C14 capacitor, located just before the mix control, is changed from 0.033uF to 0.012uF. A CE-2B with the E.Level knob turned fully clockwise will sound almost like the CE-2, but with the chorus effect applied to slightly higher frequencies.
Transforming a CE-2B into a CE-2 is simple. First, change C14 (0.033uF) to 0.012uF. The level knob acts as a short if set to the max., so the removal is not necessary, just remember to always keep it turned fully clockwise.
If you want to completely eliminate the function of the level knob, short all its 3 pins together. Alternatively, you can remove the wires that go to it and solder the 47k (yellow, violet, orange, gold) resistor directly in the board.
There are other component changes you could make, but they will not affect the quality of the sound. See the table on the right for all the differences between the two models.
Adjustment procedure for the CE-2B:
Turn the Rate knob fully counterclockwise (min.), the E.Level to middle position and the Depth knob fully clockwise (max.). Feed a 200Hz, +3dBm sine signal into the input jack. Connect an oscilloscope to the emitter of Q3 and turn VR3 to provide centered operating point as shown in the diagram on the left.