JBL MPX300 (late 1990s – early 2000s)
The JBL MPX300 is a professional power amplifier from JBL's MPX series. It's the entry-level model, sitting below the MPX600 and MPX1200. It was built for installation and tour-grade duty. The chassis is 2U and rack-mountable, with XLR and ¼" TRS balanced inputs and barrier strip outputs. The topology is Class AB, rated at 300W RMS per channel into 4 ohms (190W into 8 ohms). It bridges to mono. A pair of temperature-controlled 12V fans handle cooling, and owners note those fans are audible in quiet rooms. That's fine for live sound.
The specs are solid for the era. Frequency response is 20Hz-20kHz ±0.5dB, THD is under 0.05%, signal-to-noise is above 100dB, damping factor is over 200, and input sensitivity is 1.2V. The unit weighs around 12.6kg, though one source lists 13.2kg and the discrepancy is unresolved. A 1999 JBL price sheet listed it at US $649. Production years aren't precisely documented, but the series appears to date from the late 1990s into the early 2000s.
Owners on pro audio forums describe it as reliable and clean-sounding, with ample headroom for small-to-mid PA work. The common complaints are the fan noise mentioned above and, on aging units, crackling output from worn relay contacts. That's a straightforward fix. JBL no longer manufactures MPX series modules, though third-party shops offer capacitor kits for recapping. Used prices in 2023-2024 ran $200-$350 depending on condition.
Known specs:
- 300W RMS per channel @ 4Ω; 190W RMS per channel @ 8Ω
- Frequency response: 20Hz–20kHz ±0.5dB
- THD: <0.05%
- S/N ratio: >100dB
- Damping factor: >200
- Input sensitivity: 1.2V
- Dimensions: 483mm × 88mm × 385mm (2U)
- Weight: 12.6kg (one source says 13.2kg)
EQ Magazine (February 1995, p.102) covered the MPX series in the context of professional sound reinforcement. It noted the value of keeping outboard gear in the signal path without disturbing normal console flow.
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