JBL M644 4-Channel Amplifier

Documentation on the JBL M644 is thin, and even the basics are a little elusive. What the record shows: it's a 4-channel Class A/B amplifier built around speaker-level inputs. The JBL database lists it with two pairs of stereo/mono inputs and four pairs of outputs — so it could take a speaker-level signal from a head unit and distribute amplified signal to four channels. Power ratings are given as 40 watts continuous average per channel into 4 ohms, 50 watts into 2 ohms, and 120 watts bridged into 4 ohms.

Beyond those specifications, almost nothing else is documented. No frequency response, distortion, or signal-to-noise figures appear in the available sources, and no original price or production years have surfaced. What little community discussion exists is positive but anecdotal — one owner reports his unit "works fine," another notes having found the circuit diagram on HiFi Engine. The M644 appears to have been sold as an amplifier board, likely for custom installations. EQ Magazine (August 1992, p.110) ran a piece on weak links in sound systems around this era, but the M644 itself never received a proper review in the publications we track.

Known specs: