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The QSC CMX300Va 430W Professional Power Amplifier is a 2 RU power amplifier designed for live sound reinforcement applications such as for performance halls, houses of worship, sports clubs, gymnasiums, dance venues, pubs, and more. The amplifier uses a powerful, high-current toroidal transformer with filtering to ensure sufficient energy reserves, allowing the amplifier to handle high-level transients, even when driving 2-Ohm speaker loads.

The output section features a Class AB architecture, which reduces AC current draw and cuts down on unnecessary heat. Automatic current limiting protects the amplifier from damage until the short is corrected. It also features DC protection systems to prevent loudspeaker damage in the unlikely event of an output transistor failure. DC voltage from the power supply is never passed directly to your speakers, even in case of an output circuit breakdown.

A full complementary output circuit using high-grade linear output devices generates a flat-frequency response with low distortion. SMT (Surface Mount Technology) triples small-signal component density, enabling high power output in a 2 RU chassis, less than 16" deep. The output devices are directly mounted to the heat sink to improve thermal coupling and cooling.

The unit can directly drive 70 distributed loudspeakers in mono mode. For installations requiring a transformer isolated output, the CMX has optional accessories to accommodate different applications. The QSC CMX300Va ships with a power cord and a security plate.

More Information

QSC CMX 300V Amplifier in used but working condition.

QSC CMX-300V POWER AMPLIFIER 2x300W RMS @ 4Ω, 2x430W RMS @2Ω, bridged (mono) 830W RMS @ 4Ω.

  • “Flex-Use” loading options allow you to drive low-impedance loads down to 2 ohms and certain models to drive 70 and 100V distributed loudspeaker systems
  • “Flex-Use” Input connectivity choices including actively balanced barrier strip, XLR, or 1/4″ TRS
  • “Flex-Use” Output connectivity choices include NL4 Speakon™ and detachable terminal block
  • Rack mountable with chassis less than 16″ or 40.6 mm deep
  • 1 dB recessed, detented gain controls for fast, accurate and repeatable settings
  • Tamper-proof security cover for gain controls
  • Recessed rear DIP switches for easy selection of stereo, parallel, or bridged mode operation, and the additional choice of enabling/disabling low frequency filter protection
  • Low-noise variable-speed fans with rear-to-front airflow keep amplifiers and racks cool

Technical Specification


QSC CMXa Specs
Number of Channels 2
Power Rating 8 Ohms:
185 W per Channel (Full Range, 0.1% THD)
200 W per Channel (1 kHz, 0.1% THD)
530 W Bridged (Full Range, 0.1% THD)
600 W Bridged (1 kHz, 0.1% THD)

4 Ohms:

280 W per Channel (Full Range, 0.1% THD)
300 W per Channel (1 kHz, 0.5% THD)
830 W Bridged (1 kHz, 1% THD)

2 Ohms:

430 W per Channel (1 kHz, 1% THD)

70 V:

600 W Bridged (1 kHz, 1% THD)
Amplifier Class Class-AB
Protections AC Coupling, On/Off Muting, Reactive/Mismatched Load
Frequency Response 20 Hz to 20 kHz ±1 dB
5 Hz to 50 kHz (-3 dB)
Damping Factor > 300 at 8 Ohms
Input Sensitivity 1.15 V / 3.4 dBu (at 8 Ohms)
Input Impedance 10 Kilohms (Unbalanced)
20 Kilohms (Balanced)
Max Gain 30 dB (at 8 Ohms)
Max Input Level +22 dB / 10 Vrms
SNR > -100 dB (at 8 Ohms)
THD 4 / 8 Ohms:
< 0.03% (Full Range, at Rated Power -10 dB)
< 0.03% (1 kHz, at Rated Power)
Intermodulation Distortion < 0.02% (SMPTE)
Analog Audio I/O 1 x Barrier Strip 5-Pin Input
2 x 
XLR Balanced Input
2 x 
1/4" TRS Balanced Input
1 x 
Block 6-Pin Output
2 x 
speakON Output
AC Input Power 120 VAC, 50 / 60 Hz
230 VAC, 50 / 60 Hz
Current Consumption 120 VAC, 4 Ohms:
4.4 A (Typical, 1/8 Power)
6.6 (Severe, 1/3 Power)

230 VAC, 4 Ohms:

2.2 A (Typical, 1/8 Power)
3.3 (Severe, 1/3 Power)
Display & Indicators Green LED (Power)
Green LED (Signal, per Channel)
Red LED (Clip, per Channel)
Cooling Fan (Variable Speed)
Dimensions 3.5 x 19.0 x 15.9" / 8.9 x 48.3 x 40.0 cm
Weight 35 lb / 15.9 kg
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