Kramer 920 power amplifier, can I use this to run a sub?

[fruit67]

https://www.markertek.com/product/kr-92 ... 2FR-LSx7Nb
Hi There
I recently aquired this amplifier? Not sure what it is exactly. Can I use it to run a big sub?

Thanks

[forumuser931182]

Unfortunately this amp is designed to drive ceiling speakers ( as in an office environment ) hence the 70/100v output. Not the amp you want.

[Wonks]

As it stands, no.

It's a 70v or 100v (presumably this is selectable on the unit) line amplifier. Designed for powering multiple small speakers, often as a PA or background music system in a building. It needs to be used with speakers that have a transformer attached, rated for the necessary power.

Say you had 20 speakers you wanted to provide a common power signal for at 10W each. If you used standard 8 ohm speakers, the parallel resistance equivalent would be 0.4 ohms, far too low for a standard power amp to drive.

Instead you use a power amp that has an output transformer internally attached, that will provide a signal voltage of 70 or 100 volts (70v is typically a US voltage, 100V is typicallyUK/EU) at full output. Each speaker has a transformer that will provide 20W into an 8 ohm load when provided with the selected line voltage.

You don't have to have the same wattage taken by each speaker. If you had a small room, you might want 3W of power (here the W rating is a measure of relative loudness, not power handling capacity as for a standard speaker) and in a bigger room a 5W speaker.

This type of small power PA speaker will often have multiple tappings on its transformer, say 8W, 4W, 2W and 1W, so you can use the same speaker in different locations at different output levels.

Using a transformer at the amp and the speaker isn't ideal regarding efficiency, but it allows you to a) use one amp to drive a lot of speakers with the same signal and b) use smaller diameter connecting wire, as boosting the signal voltage drops the current required for the same overall power level, and smaller diameter wires are cheaper.

Now you could try and find a suitable transformer that provided 200W into 8 ohms from a 100v line feed, and fitting that into an external enclosure, but really you are better off moving that power amp on and buying something more suitable.

[Folderol]

I'd add that these amplifiers often have a deliberately limited and tailored frequency response as they are expected to be used principally for speech.

[ef37a]

I'd add that these amplifiers often have a deliberately limited and tailored frequency response as they are expected to be used principally for speech.

Very true^ Such amplifiers also usually have very aggressive V/I limiting circuits as well since the output lines can easily get shorted or peeps tend to just add extra speaker loads as the factory expands!

Dave.