Boss NF-1 Noise Gate pedal schematic diagram

The Boss NF-1 Noise Gate pedal contains a simple circuit that cuts off all sound as soon as the signal level falls below a threshold level adjusted with the SENS knob. You can set how fast you want the sound to disappear with the DECAY pot.

Boss NF-1 Noise Gate Pedal Schematic Diagram Fig. 1: Boss NF-1 Noise Gate guitar pedal schematic diagram
Boss NF-1 Noise Gate PCB (component side) ET-45C (151-045C)
Fig. 2: Boss NF-1 Noise Gate circuit board Boss NF-1 Noise Gate adjustment - oscilloscope signal
Fig. 3: Boss NF-1 Noise Gate adjustment
Boss NF-1 Noise Gate guitar pedal picture
Specifications:
  • Controls: Sens, Decay
  • Connectors: Input, Output, AC Adaptor
  • Input Impedance: 220kΩ
  • Output Load Impedance: over 10kΩ
  • Maximum Output Voltage: +9dBm
  • Current Draw: 3.9mA (DC 9V)
  • Recommended AC Adaptor: ACA Series
  • Dimensions: 70(W) x 55(H) x 125(D)mm
  • Weight: 400g

ICs, transistors and diodes used in the Boss NF-1 Noise Gate pedal:

  • IC1: uPC741C (operational amplifier IC)
  • D1: RD11EB (11V Zener diode)
  • D3, D3: RD4.7EB (4.7V Zener diode)
  • D4-D8: 1S1588 or 1S2473 (switching diodes)
  • Q1, Q2: 2SC732TM-GR (NPN silicon transistors)
  • Q3: 2SK30A-Y (N-channel JFET transistors)
  • Q4-Q9: 2SC1815-Y (NPN silicon transistors)

Adjustment procedure:

1) Set the Sens knob fully counterclockwise and the Decay knob fully clockwise.

2) Connect an oscilloscope to the effect's output through a millivoltmeter. Feed a 1kHz -45dBm sine signal to input.

3) Adjust VR3 and VR4 for the values shown in Fig.3.

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