Operadio PA amp, 5000 ohm output?

[cburbank]

Hello,

I have an old Operadio 1A65. The schematic can be found here:

http://www.theused.com/resource/resource.php?curPage=27

I am wondering why the output impedence is so high? Is this really just a pre-amp? If so, what kind of power amp would accept this 5000ohm signal?

Is there such a thing as a 5000ohm speaker.

Any information is appreciated. Thanks!!!

[Enzo]

SOmeone might have a 5000 ohm headphone.

This is a line amplifier, not a power amplifier. Well, a PA system mixer really. That output tube is a 6SN7, and that isn;t going to power much speaker.

The output transformer allows you to match the output to a wide range of impedances, from 10k ohms (5000-0-5000), down to 125 ohms. You can drive a balanced line or a single ended line.

[cburbank]

Thanks for the reply!

So if it's very low output (I've noticed that myself,) is it really designed to drive a speaker directly?

If it is designed to go into a power amp, (even a solid state one) which taps would I use, and should I set it up for single ended or balanced line?

Ideally I would like to use this for background music, guitar, or as a vocal amp.

Thanks!

[Enzo]

It is a line amp, it is not meant to drive a speaker.

Experiment with connections to a power amp. If the amp has balanced inputs, try that, otherwise, single ended. Of single sided, start with as high an impedance as possible.

[cburbank]

Thanks again!

Any guidelines for impedance to use on the balanced input? Is there a typical range that power amps would be expecting?

How will I know if I'm off? Poor signal quality? Excessive volume or too quiet?

Naturally I don't want to fry anything on either end!!!

[Steve Conner]

Yes, that's how you'll know if you're off: poor signal quality, excessive volume, or too quiet, or things getting fried.

I'd start with the 125 ohm tap and work up from there.

The output is transformer balanced, so it should be able to drive any kind of power amp input, either balanced or single-ended, without problems. It'll probably work best if you leave off the ground jumper mentioned in the instructions, unless your power amp isn't grounded.