600 OHM Balanced Line Audio Amplifier with Tunable Notch Filter / Bandpass Filter / Low-High Pass Filter with AGC

Notch, Bandpass High Pass, Low Pass Filter,  - Line Ampli

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NFBF-10 Product Manual



Midian's NFBF-10 is a single channel 600 ohm balanced line audio amplifier with a tunable notch filter and AGC as well as an adjustable gain output stage. It can be used in several ways. It may serve as a simple single channel line audio amplifier, an AGC amplifier, a tunable notch filter, or a combination of these functions. It's most common use it to remove the 2175 Hz tone remote keying tone from voice recording systems and 1950 Hz Pilot Tone from voting systems. A high pass, low pass, bandpass filter can be effected through the use of jumpers.


Notch Filter: As a notch filter, the NFBF-10 will remove the undesirable tone from the incoming audio while passing the rest of the audio. The NFBF-10A is commonly used to remove 2175 Hz keying tone from tone remote radio dispatch systems going into a voice recorder. The NFBF-10C is used to remove CTCSS tones from audio.

Band-Pass Filter: As a band-pass filter, the NFBF-10 will block all audio except for the desired frequency.

High Pass / Low Pass Filter: Through the use of jumpers, a high pass or low pass filter can be created by eliminating the bandpass or notch filters.

600 OHM Balanced Line Audio Amplifier: Has an adjustable input gain control and an adjustable output gain control.

AGC Amplifier: Has a jumper selectable AGC Amp that can be installed between the input and the line driver amplifier.


This product comes complete in a box with 600 ohm balancing transformers and a wall power adaptor. The product has an RJ-11 input (source audio) and an RJ-11 output (destination audio) with the middle pair being used for 2-wire audio.