QSC GX3 Power Amplifier (300 Watts)

Get QSC quality on a real-world budget. The GX3 300-watt power amp has an onboard crossover to drive your sub, and GuardRail limiting to protect your PA.

The QSC GX3 amplifier is the smallest-output amplifier in the much-acclaimed QSC line. To 8 ohm speakers, it delivers 300 watts of output in a 2-channel speaker system, and 350 watts in a single channel output. To 4 ohm speakers, it delivers 425 watts of output when driving a 2-channel setup, and 500 watts as a single channel output. The QSC GX3 is a true Class B biasing amplification system, yielding excellent heat gain management and the peerless audio quality that we have come to expect from QSC. At this wattage and size, the QSC GX3 would be best suited to driving the PA in a small venue or other intimate setting, or for driving onstage monitors.

I/O Designed for Contemporary Applications

The GX Series amplifiers are designed with an I/O intended to be useful for the greatest number of contemporary musicians and DJs. It features a single balanced XLR and 1/4-inch TRS on BOTH channels. It also has RCA phono connectors to hook up with whatever other audio source you may be running through this amp. A 100 Hz LF/HF Crossover switch allows you to toggle to and from Full Range mode.

The GX3 also features a Speakon combo XLR/TRS connector on each channel with 2-pole and 4-pole plugs. There are also positive/negative binding posts here to cover all other speaker wiring configurations.

GuardRail: QSC's Proprietary Heat and Volume Gain Limiter

Every amplifier in the GX Series makes excellent use of its onboard GuardRail system, which combines Clip Limiting and Thermal read more Limiting into a single active system. QSC intelligently recognized that most power amps are used at the highest possible output at all times, and that clipping derived from heat gain or speaker overdrive should be taken for granted as a problem facing most users.

Its unique design works by measuring the onset of clipping, showing you the peak level via the Clip LED light. It automatically factors the variables of Load Impedance, AC voltage, and power supply and compensates in kind. This way, a milder triggering of the Clip LED does not necessarily trigger the Clip Limiting. Instead, the GX amps target heavy and prolonged clipping, causing a "slow" limiter to gradually reduce the dynamics until the amount of clipping is deemed reasonable. This design aims to do better than other peak limiters by seeking not to eliminate ALL clipping -- but only to intervene as gently as possible on excessive peaks and distortion. This avoids the dramatic and unpleasant "drop out" moments created by other powered speakers that effect substantial gain decreases at the first sign of clipping.

The GX Series also utilizes this feature to compensate for overheating. In such situations, the gain is gradually reduced to prevent the need for thermal muting. Overall, the GX Series does better than other power amps by limiting peak clipping only as much is as absolutely necessary.

The Essence Of Strength and Portability

The QSC GX3 is made of an all-steel case, in a minimum-depth chassis. It will fit in any compact rack mount.


- 2 x balanced XLR and 1/4-inch TRS (one on each channel)
- RCA phono connectors
- Speakon combo XLR/TRS connectors (on each channel)
- 2-pole and 4-pole plugs
- Positive/negative binding posts
- 100 Hz LF/HF Crossover switch
- GuardRail Heat and Peak limiting system
- Clipping monitor LED light
- All-steel chassis
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Output watts per channel:
- 8 Ohms / both channels driven: 300 Watts
- 8 Ohms / single channel driven: 350 Watts
- 4 Ohms / both channels driven: 425 Watts
- 4 Ohms / single channel driven: 500 Watts
- 2 Ohms / both channels driven: 200 Watts

Note: This power amplifier does not have a bridge mode.

- Signal to Noise (20 Hz - 20 kHz): 100 dB
- Input Sensitivity: 1.2 Vrms
- Voltage Gain (8 Ohms): 32.2 dB
- Output Circuitry: Class B
- Power Requirements: 6.3A
- Frequency Response: 20 Hz - 20 kHz, +0, 1 dB
- Dynamic Headroom (4 Ohms): 2 dB
- Damping Factor: 100
- Input Impedance: Greater than 20k (balanced)
- Maximum Input Level: +24 dB (16 Vrms)
- Input Connectors (each channel): 3-pin XLR and 1/4-inch TRS, balanced, parallel Phono, unbalanced
- Output Connectors (each channel): Speakon, 1/4-inch, Binding Posts
- Amplifier and Load Protection: Short circuit, open circuit, thermal, RF protection Load protected against DC faults
- Rear Panel Controls: Full Range / Crossover switch
- Dimensions (H x W x D): 3.5 x 19 x 10.1 inches (89 mm x 483 mm x 257 mm)
- Weight: 25 lbs (11.5 kg)

- 8 Ohms: less than 0.05%
- 4 Ohms: less than 0.1%

Front Panel Controls and Indicators:
- Gain controls, 21 detents
- Red Clip LEDs, proportional, 0.1% THD threshold
- Green Signal LEDs, threshold -35 dB
- Blue Power LED, AC on
Dimensions and Weight in Packaging
Base Item
Shipping Weight: 29.25 lbs
Shipping Dimensions: 24 x 15 x 6 in
Manufacturer Part Number (MPN): GX3120V

For support or warranty questions, please contact the manufacturer:
Phone: 800-772-2834
Web: http://qsc.com/support

QSC GX3 Power Amplifier

GX Series amplifiers are ideal for professional entertainers who require maximum performance and portability on a limited budget. QSC designers, headed by Pat Quilter, have optimized output and appearance while reducing raw material cost and weight. It's all here - dramatic styling, easy hookup and adjustments, excellent audio quality and QSC reliability.

GX amplifiers deliver just the right amount of power to the most popular speakers used by entertainers. Most loudspeaker manufacturers recommend an amplifier with power output equal to the speaker's "Program (Music) Power" rating or two times (2 x) the "Continuous (RMS) Power" rating.

The GX3 is ideal for speakers in the 300 watt (Program) range. This model supplies the maximum possible power to 4 ohm and 8 ohm loads. Owners of popular 4 ohm loudspeakers (dual-woofer, two-way models and many subwoofers) will find the 700 watt (4 ohm) power of the GX5 an ideal match.


- Optimized for maximum real-world headroom into 4 Ohm and 8 Ohm speaker systems
- Inputs: XLR, 1/4-inch TRS and phono input connectors for compatibility with any source
- Outputs: Speakon combo accepts, 1/4-inch (TS) plugs or Speakon 2-pole and 4-pole plugs (connects 2 poles only).
- Binding posts support all other speaker wiring systems.
- Minimum depth chassis (10.1 inches/257 mm)
- Fits in compact, inexpensive effects racks
- Lightweight - less than 26 lbs (12.5 kg)
- Detented gain controls for precise setting and matching of sensitivity
- GuardRail automatically protects the amplifier and loudspeakers from damage due to temperature rise or overdrive without shutting down the show
- Front panel LEDs monitor Power, Signal and Clipping
- Subwoofer/Satellite crossover built-in

GX amplifiers deliver just the right amount of power to the most popular speakers used by entertainers. Most loudspeaker manufacturers recommend an amplifier with power output equal to the speaker's Program (Music) Power rating or two times (2 x) the Continuous (RMS) Power rating. The GX3 is ideal for speakers in the 300 watt (Program) range. The GX3 supplies maximum possible power to 4 ohm and 8 ohm loads.

Technical Notes

The GX3 uses the QSC Grounded Collector output system, for optimum cooling of the critical power transistors. A true Class B biasing system combines maximum thermal efficiency with excellent audio performance. QSC design expertise allows the output devices to shift from low-power to high-power rails in less than a millionth of a second, ensuring that the output power is always right where it needs to be without excess loss.

The amplifier uses premium toroidal power transformers for reliable mid-weight performance. A variable-speed fan moves air crosswise through the amplifier, drawing cool air in over the power transformer, through the fan, and then over the heat sink. This keeps the transformer cool and allows a full size heat sink to fit in a down-sized chassis. As always, the amplifiers are fully protected from the usual hazards of the trade, ensuring stable performance and long life.

GuardRail Limiting Protects Your Speakers

GuardRail protection delivers full peak power while preventing detrimental overloads. During excessive clipping, or extreme overheating, GuardRail reduces gain just enough to preserve the integrity of the music, protect the speakers and keep the audience excited, without unprofessional distortion levels or shutdowns.

Subwoofer/Satellite Crossover

A subwoofer reduces strain on the full-range speaker, allowing it to play louder, or letting a smaller speaker do the same job. The GX Series supports this mode with a Crossover switch that splits the full-range input entering Ch 1, sending 20 Hz -100 Hz to the sub (Ch 1) and 100 Hz - 20 kHz to the top box (Ch 2). The front panel gain controls balance the sub and top box, while GuardRail optimizes peak power into the sub and top individually, for greater musical impact and dynamic range.

Reviewers gave this product an overall rating of 4.5 out of 5 stars. (20 ratings)
Submitted April 8, 2015 by Randy D in Wellsville, NY
"QSC GX3 Power Amplifier is a great deal"
Overall: 4.5 out of 5 stars
(see rating details)
Verified Customer zZounds has verified that this reviewer made a purchase from us.
I am on a limited budget ,just like some other folks. I had a Yamaha PA system that was stolen,that hurt really bad. Sooo..I have been attempting to build a new PA system on a budget,piece by piece. I came across a mint condition pair of Peavey SP 3G's for $250.00 ...that was a steal. I found a blemished Beringer mixer for $40.00. I saved some money and purchased some quality cables.Now it is amp shopping time..I knew that (from previous experience) QSC makes fine equipment. I knew I needed more power for the cabs I had purchased...but I figured that I would order this GX3 and would upgrade later. I needed some sound after this long wait. WOW!! I am impressed with this amp. I know my cabs can handle more power...way more..but this lil amp impressed me.I must tell you that I normally do not take the time to do reviews on products. I just had to with this purchase.
Sounds great....very tight mid bass..screaming mids and highs.
I like the input and output options.
Ease of Use
Pretty simple to hook up...plug in and play.
Seems pretty well built to me.
Great value in my opinion. It's performance actually exceeded my expectations as far as the money I spent.
Manufacturer Support
Worked great out of the box.
The Wow Factor
The wow factor would be the fact that it gives you some quality sound for your hard earned $$$.
Musical Background:
Drummer for 21 yrs, DJ for an occasional wedding, karaoke bar gigs, jam at home with friends
Musical Style:
rock ,blues, and some classic country
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