JBL MPA600
Little is documented about the JBL MPA600 from manufacturer sources, but the service manual survives and settles most of the important questions. It's a two-channel professional power amplifier rated at 600W continuous per channel into 4Ω, 400W into 8Ω, and 1200W bridged into 8Ω — all measured across 20Hz–15kHz at 0.1% THD, with the output protection circuit deliberately preventing full power above 15kHz. Midband (1kHz, both channels to the onset of clipping) is higher: 674W into 4Ω, 450W into 8Ω, 1600W bridged. Frequency response is quoted as 20Hz–20kHz ±0.1dB, extending 8Hz–100kHz at +0/−3dB. The output stage is a complementary two-step linear high-efficiency design — the service manual's parts list confirms the 2-step topology is specific to the MPA600, MPA400, and MPA750, while the MPA1100 used three steps and the MPA275 a single step.
It's a 2U rack unit, 19 inches wide and 17.9 inches deep including the rear support ears, and it weighs 20kg net. Cooling is a continuously variable rear-to-front fan. Per the manual's test procedure, the MPA600's fan stays off until the unit heats up, unlike the larger MPA750 and MPA1100, which spin up immediately. Inputs are barrier strip and XLR. Outputs are 5-way binding posts and Neutrik Speakon, and a rear mode switch selects Bridge, Parallel, or Stereo. Input impedance is 10kΩ unbalanced or 20kΩ balanced, with 1Vrms sensitivity for rated power into 8Ω and 35dB voltage gain. Protection covers short circuit, open circuit, ultrasonic and RF, thermal limiting and muting, DC-fault load grounding via relay, clip limiting, and on/off muting. The manual notes the output is AC-coupled through filter capacitors, which eliminates the need for DC load protection.
Dating is the weak spot. No production years or original MSRP are confirmed. Japanese price references put it around ¥380,000 circa 1993 and ¥250,000 circa 1997, which suggests a run through the 1990s but isn't proof of production dates. JBL offered optional input cards under its "Open Input Architecture": a stereo 2-way crossover (IM-10), subwoofer high-pass (IM-11), cinema crossover (IM-12), and input expansion module (IM-30). The amplifier's output limiter was designed to track the power-compression behavior of JBL's PA speakers. A forum claim holds that the MPA and MPX series were built for JBL by QSC, though that's user comment rather than manufacturer documentation.
Period coverage is thin. Mix (February 1994, p.126) ran only a preview of related pro-audio gear in its new-products column, so reception rests on owner reports. "Built like a tank" recurs, alongside complaints about noisy fans at idle and input jack solder joints cracking after road use. Used examples turn up in the low hundreds of dollars or euros. The 12-page service manual is the reason this page can state specs with confidence at all.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.
Related Models
- JBL 5231 (1974)
- JBL 5232 (1974)
- JBL 5233
- JBL 5234
- JBL 5235
- Eico 3150 (1967)
- Fisher CUSTOM-ELECTRA-I (K-14/K-15) (1957)
- Fisher CUSTOM-ELECTRA IV (E33/E44) (1960)
- Akai AM-2400 (1978)
- Akai AM-2600 (1977)