Thread: Identify Amp/Determine Output

Hi All,

I'm totally green on speakers & amps but I'm looking to do some diy stuff.
I'm hoping to get some help matching a mystery amp to the proper speakers.
Here are the details; I bought at a garage sale the amp only portion of an old powered PA/monitor cab. The cab/speakers were long gone. The amp has absolutely no markings of manufacture, brand or output anywhere. There is nothing on the faceplate or anywhere on the circuit boards. I can find a few part numbers but they don't provide any leads in finding the brand and/or output specs.
I would like to drop this amp into a speaker cab but I want to make sure I get something that can handle the amp. I know the amp works, I've been able to connect it to some speakers and get some sound but I want make sure I have the right equipment.
Can someone provide some guidance to figure out the peak wattage, rms and any other important details that I would need to complete this project?


Thanks.

So, I've added pictures to see if anyone can identify the brand of this amp...

Thanks.

I am speculating here but it looks like a 4A fuse for 120v, 2A fuse for 230V so that defines a power input to the amp (4x120 or 2x230). The power output of the amp can exceed that in the short term but will over the long term average out to a fraction of that total available input power.

JR

Put a 1k sine wave through the amp, scope the output. Turn it up till you see it clip, measure the voltage, square that and divide by nominal impedance of your load. Bingo, there's your wattage (at least into 1k).

Whether the amp will sustain that wattage for any length of time is dependent on the amp, the heat dissipation, and how big of a load it is.

Paul,

It's probably not a lot of power. Plug it into your speaker. Don't turn it up all the way to start.

Originally Posted by Silas Pradetto

Put a 1k sine wave through the amp, scope the output. Turn it up till you see it clip, measure the voltage, square that and divide by nominal impedance of your load. Bingo, there's your wattage (at least into 1k).

Whether the amp will sustain that wattage for any length of time is dependent on the amp, the heat dissipation, and how big of a load it is.

You really need to have a dummy load hooked up. The amp may swing a good bit more with no load than with a load. Start with an 8 ohm load and then try 4 ohm. See how the amp reacts.

If you see any "weirdness" on the oscope-(other than clipping), then it does not "like" that impedance.

Originally Posted by Silas Pradetto

Put a 1k sine wave through the amp, scope the output. Turn it up till you see it clip, measure the voltage, square that and divide by nominal impedance of your load. Bingo, there's your wattage (at least into 1k).

Whether the amp will sustain that wattage for any length of time is dependent on the amp, the heat dissipation, and how big of a load it is.

When you measure voltage on a 'scope it is in peak-to-peak. Divide that by 2 to get peak voltage. Then multiply by the inverse of the sq rt of 2 (.707) to get Vrms. Then Vrms squared / Z = power (nominal).