wiring a PA amp...

Here's my useless answer. I have no clue why a solid state amp would have different outputs for different speaker impedances. Tube amps use a transformer to make the tubes "see" the right impedance to keep them linear and non distorting to the highest levels possible, and multitap transformers are common in tube amps. Solid state amps, as far as I have seen, just don't care what the imipedance of the attached speakers may be, until that impedance gets low enough that the amp will overheat when driving the impedance hard. But typically a solid state amp that is specified to be able to handle a 2 ohm load uses the same outputs for a 2 ohm load as for a 16 ohm load. Thus my cluelessness.

Yes, that sounds like a tube amp or an early 1960s solid state amp with an output transformer.

McIntosh did use an autotransformer in their early solid state amps as well.

A true PA amplifier has a so-called "70-volt" output to drive PA speakers. That is what you need for a PA system.

It does not actually put out 70 volts (unless turned up to full volume), but it does put out a lot more voltage than a normal amplifier output..

A PA setup uses speakers that have a matching transformer mounted on each one, with several taps that can be used to adjust the relative volume of the individual speakers with respect to each other and the room size/location. You adjust the speaker volume by moving one of the speaker wire lugs from one transformer terminal to another until you get the amount of sound you want (with the amplifier set to an appropriate volume).

All the speakers are wired in parallel; one pair of wires goes to the first speaker, and on to the next speaker, etc. etc. As many as 10 speakers can usually be connected to an amplifier in this way. Each speaker is a relatively high-impedance load due to its transformer.

With hookup you describe, you would want to use the 8 ohm output terminals on the amp. The 3rd speaker will be twice as loud as the others.





Edited by commsysman - 2/4/13 at 9:59pm

Gee, the last concert I went to didn't use a 70 V PA...I guess it wasn't a 'true' PA system.

no they're not....the transformer primaries are.

PA stands for "public address" which is usually for announcements and background music in buildings, or to amplify the voice of someone speaking to an audience at a microphone in an auditorium etc.

They don't use PA systems at concerts; they use high-powered pro-audio systems.

..

...or musical instruments...like at a concert

According to you....

... of course, you've been proven worng so many times in these fora, it's actually funny when you post.

Any 70V amp can deliver 70V even when the volume control is well below )full volume". The "volume control" has nothing to do with the output voltage or power capability. It is simply a gin control.

Turn the control down and drive it harder and you can get full output unless the level is turned all the way down.

And it won't put out 70V (a BIG MISCONCEPTION many people have) unless it is driven hard enough. And even then it is not a constant 70V-but rather a 70V average music signal.

I don't know what you consider "a lot more voltage", but an amp that can deliver 600 watts into an 8 ohm load is a "70V" amp. That is not that big of am amp these days.

Being the king of typographical errors, I am far from casting aspersions. But the concept of an amp having a "gin control" tickles me . . ..

Hopefully it also has tonic controls.

And a lime button. Gotta have the lime.

That button works best if there's also a coconut button.

I have been to acoustic and classical concerts that didn't use a PA, but every rock band uses them.