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power amps
Old 10th July 2019
Here for the gear

power amps

Hi everyone, i'm new here. i have a question, can anyone tell me what a power amp is used for? and how do they work
Old 10th July 2019
Gear Addict

For powering passive monitors.
Old 11th July 2019
not to sound like a smart ass, but a power amp takes a quiet signal and makes it loud. As Dave above explains, a line out signal is very quiet and a power amp takes it and steps it up to make it audible.

If you plug in a set of headphones into a guitar, you probably won't hear anything. But, plug that guitar into a guitar amp and it amplifies the signal so it can be heard.
Old 13th July 2019
Lives for gear

Power amps take a line-level signal and amplify it to drive passive monitors. Consoles, tape decks, compressors, EQs, and mic pre's all have line-level outputs. As power amps generally don't have volume controls, you control the volume from whatever gear is upstream.

A line-level signal is typically 0.75 V for unbalanced (RCA) connectors, or 1.5 V for balanced (XLR) connectors. Power amps have high input impedance so they don't load, or impinge on the output of the upstream gear.

They are designed to drive passive monitors, which typically have a nominal input impedance somewhere between 4-16 ohms. Impedance varies with frequency, sometimes wildly. Sometimes it's good to know the minimum input impedance of a monitor, especially if your power amp is unstable into a low-impedance load.

As monitors' efficiency, or sensitivity, varies widely, some do well with low-powered amps, and others require lots of power. Power is typically spec'd as "x" watts rms (average) into an 8-ohm load. The spec can be more meaningful if it includes the total harmonic distortion (THD) figure, and if it includes the frequency range, typically 20-20,000 Hz. The key is the rms watt output into a specified input impedance.

When selecting a power amp for a specific monitor, make sure it has enough power so you never approach its limits. All power amps can output far more power than their specs suggest, though it's highly distorted. That's how low-powered amps can fry tweeters. The guideline is: have plenty of power on hand, and don't turn it up too loud.

Pic is a mono tube amp that has both RCA and XLR inputs.

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Last edited by Bill Way; 13th July 2019 at 08:39 PM..
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