Boss BF-2 flanger pedal schematic

The BF-2 was first sold in 1980, but it's still is one of the most commonly used analog flanger pedals. The 4 knobs (manual, depth, rate and resonance) allow the users to shape the sound as desired -- from dynamic jet-plane effects to short delay, chorus and vibrato sounds.

Schematic diagram of Boss BF-2 flanger pedal Fig. 1: Boss BF-2 flanger guitar pedal schematic diagram
Boss BF-2 flanger PCB (component side) ET-54 (151-054)
Fig. 2: Boss BF-2 flanger circuit board - component side
Boss BF-2 flanger pedal picture

Specifications:

  • 4 controls: Manual, Depth, Rate and Resonance (Res)
  • Connectors: Input, Output, AC Adaptor
  • Input impedance: 470k
  • Residual noise: -95dBm (IHF-A)
  • Output load impedance: over 10k
  • Delay Time: 1ms - 13ms
  • LFO speed: 100ms - 16s
  • Recommended AC Adaptor: ACA or PSA Series -- depending on production year
  • Current draw: 15mA DC at 9V
  • Weight: 400 g (0.88lbs.)
  • Dimensions: 70(W) x 55(H) x 125(D) mm. (2.8" x 2.2" x 4.9")

ICs, transistors and diodes used in the Boss BF-2:

  • IC1, IC2: uPC4558C (dual operational amplifier)
  • IC3: MN3207 (1024 stage BBD)
  • IC4: MN3102 (BBD driver)
  • IC5: TL022CP (dual low-power general-purpose operational amplifier)
  • IC6: uPC78L05 or equivalents (5V positive voltage regulator)
  • Q1, Q2, Q3: 2SC732TM-GR (NPN silicon transistor)
  • Q4: 2SK30A-Y (Silicon N-channel junction field effect transistor)
  • Q5: 2SA733-P (PNP silicon transistor)
  • Q6-Q11: 2SC945-P (NPN silicon transistor)
  • D1: RD11EB-3 (11V 500mW Zener diode)
  • D2: RD5.1EB-3 (5.1V 500mW Zener diode)
  • D3-D10: 1S2473 or 1S1588 or DS442 (switching diodes)

Adjustment procedure:

1.) Clock frequency adjustment:
Set MANUAL and DEPTH knobs to full counterclockwise. Connect an oscilloscope to TP-1 test point. Adjust VR7 for T=25us (40kHz). Rotate the MANUAL knob fully clockwise. T should be 2uS +/-20%.

2.) BBD bias:
Set DEPTH and RES. knobs full counterclockwise. Feed a 200Hz, sine wave, 0dBm signal into the INPUT jack. Connect the oscilloscope to Q3's emitter. While turning MANUAL across its entire rotation range, set VR6 for a clip-free waveform at the peaks.

3.) Resonance:
Set MANUAL, DEPTH knobs full counterclockwise and RES. knob full clockwise. Plug short circuit into INPUT jack. Connect OUTPUT jack to an amplifier and speaker. While touching a screwdriver to TP-2, set VR5 to the point where oscillation begins.

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