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Power Amplifiers

Our range of power amplifiers supplies the muscle behind passive speakers, in two and four channel rack mounting formats for bands, venues and fixed installations. Choosing one comes down to the load your speakers present, the power they need and how much rack space and cooling you can give it. Found it cheaper elsewhere? We will match the price.

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How much power do you need?

Take the continuous or RMS rating of your speakers and look for an amplifier that can deliver a little more per channel at the impedance you are actually running. Headroom protects the speaker rather than threatening it, because the common cause of a blown driver is an underpowered amplifier driven into clipping, which sends a distorted square wave into the voice coil. As a working rule, an amplifier rated around 1.2 to 1.5 times the speaker continuous power gives clean peaks without inviting trouble.

Impedance and bridging

Impedance decides what the amplifier is asked to do. A single 8 ohm cabinet per channel is the easy case. Two 8 ohm cabinets in parallel present 4 ohm, which most decent amplifiers handle, and four would present 2 ohm, which many will not. Bridging combines two channels into one more powerful mono output, but it also halves the minimum impedance the amplifier can tolerate, so a unit happy at 4 ohm stereo may only manage 8 ohm bridged. Read the rating for the exact mode you intend to use.

Two channels or four?

Two channels suit a straightforward left and right system. Four channel amplifiers earn their place where you are driving tops and subs from one box, or feeding several zones in an install, and they save both rack space and weight compared with two separate units. Check whether channels can be paired or bridged independently, since that flexibility is what makes a four channel unit worth the extra over two stereo amplifiers.

Class D, weight and efficiency

Class D amplifiers switch rather than dissipate, which makes them far more efficient and dramatically lighter than the older linear designs. For anything that travels, that weight saving is the single biggest practical improvement available. Efficiency also means less heat, so a Class D unit often needs less rack ventilation and runs quieter, which matters in a meeting room or a rack behind a bar.

Protection, cooling and rack space

Look for short circuit, thermal and DC protection, as these are what save a speaker when something goes wrong on a dark stage. Amplifiers pull cooling air through the front or the side, so leave a clear rack unit above and below anything that runs warm, and never stack an amplifier directly on top of a rack drawer full of cable. In a sealed cabinet, plan for ventilation rather than hoping.

Wiring and gain structure

Use balanced XLR or jack inputs where you can, since unbalanced runs pick up hum over distance. Set the gain so the mixer runs at its normal operating level with the amplifier attenuators near maximum, rather than driving a hot signal into a heavily attenuated input, which raises the noise floor. On the output side, use speaker cable sized for the run and terminate in Speakon where the cabinet allows it.

Frequently Asked Questions

How powerful an amplifier do I need?
Look for around 1.2 to 1.5 times the continuous or RMS rating of the speaker, at the impedance you will actually run. Headroom protects the driver, because the usual cause of speaker failure is an underpowered amplifier pushed into clipping.

Can I run two speakers per channel?
Usually yes, if the amplifier is rated for the resulting load. Two 8 ohm cabinets in parallel present 4 ohm, which most amplifiers handle. Four would present 2 ohm, which many will not. Check the rating before wiring.

What does bridging mean?
It combines two channels into one more powerful mono output. It also halves the minimum impedance the amplifier can tolerate, so a unit rated to 4 ohm in stereo may only manage 8 ohm bridged. Always read the rating for the mode you intend to use.

Is Class D better?
For portable and installed use, generally yes. Class D is far more efficient, much lighter and runs cooler than older linear designs, which means less rack ventilation and less to carry. The weight saving alone is significant on a touring rack.

Do I need four channels?
Only if you are driving tops and subs from one box, or feeding multiple zones. A four channel unit saves rack space and weight over two stereo amplifiers, but check whether channels can be bridged or paired independently.

Why is my amplifier humming?
Usually an unbalanced input over a long cable run, or a ground loop between equipment on different circuits. Use balanced XLR or jack connections where possible, and keep signal cable away from mains cable.

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