JVC AX-44 Stereo Integrated Amplifier with GM Circuit (NGNFB) Made In Japan in 1986 - This mid 1980s JVC design converts the input signal voltage to a current signal, then amplifies that current, finally converting it back to a voltage output to deliver to the amp stage. The JVC GM circuits included the Gm V Driver, Gm Volume, and Gm Selector which combined, utilize transistors in a way that achieves better sound performance by reducing noise. Essentially the technology removes sound input signal path from the front panel controls (like volume for example) whereby the controls are functioning more like "current controllers" rather than "signal input controllers". This amp features a large transformer, 10,000uf x 2 output capacitors, and will produce a clean 100 Watts RMS output with .03% THD. The amp utilizes 2SB845 and 2SB755 complimentary pairs of Toshiba transistors also used on Technics, Onkyo, SAE, Harmon Kardon, just to name a few. Many good anecdotal reviews are available on this JVC unit.

This amplifier was recently serviced by DALAUDIO. The controls and selector switches and relay were cleaned, bulbs verified and main power supply checked per specification in the JVC service manual. The physical condition is about a 7, with some small scratches. While not mint, I kept this amplifier as an example of JVC's GM characteristics. The amplifier GM circuits were all adjusted to service manual specifications. A copy of the service and user manuals are available for personal use only, please bring a thumb drive.

Features:
Preamp Amp Input/Outputs: enable this to be used as a amp or as a preamp - the GM features are only on the preamp side but you can see how it sounds with other amps!
Inputs: CD/Aux, Phono, Tuner, Tape 1, Tape 2
Speakers: You can select Speakers 1 or Speakers 2 or Both

Specifications:
Power output: 100 watts per channel into 8Ω (stereo)
Frequency response: 10Hz to 60kHz
Total harmonic distortion: 0.03%
Input sensitivity: 2.5mV (MM), 160mV (line)
Signal to noise ratio: 70dB (MM), 97dB (line)
Dimensions: 17.25"W x 4.75" H x 12 D"
Year: 1986
Made In Japan

More About GM Circuits (Summary of Benefits) - Constant Voltage Drive: focuses on driving the amplifier's power stage with a constant voltage, rather than relying on traditional current-based drive. The approach helped maintain a more stable or predictable output signal, regardless of the load /speaker impedance. By separating the volume control from the actual signal path, the GM Circuit aims to minimize the impact of volume control on sound quality, especially in regards to noise and distortion.

Reduced Output Impedance: By operating at a constant voltage, the GM circuit minimizes the output impedance of the amplifier. A lower output impedance allows the amplifier to deliver power more effectively to the speaker, resulting in a cleaner and more powerful sound. The constant voltage drive also helps to maintain a flatter frequency response, meaning the amplifier provides consistent amplification across the entire audio spectrum. This contributes to a more accurate and natural-sounding audio experience.

Reduced Distortion: The GM technology reduces distortion, especially distortion due to speaker impedance variations and non-linearity in power transistors. This results in a cleaner and more detailed sound.

Better handling of speaker impedance variations: Improved Handling of Counter-Electromotive Force (CEMF): The constant voltage drive also helps to mitigate the effects of CEMF, which can arise in speaker systems and can lead to distortion and reduced performance. The constant voltage drive and reduced output impedance allow the amplifier to handle speaker impedance variations more effectively, resulting in consistent performance.

Reduced distortion due to power transistors: The GM technology minimizes distortion caused by the inherent non-linearity of power transistors, further contributing to a cleaner sound. More accurate and natural-sounding audio is the result. The flat frequency response and reduced distortion contribute to a more accurate and natural-sounding audio experience.