70v PA amp?

[digitalchaos]

I'm looking at setting up whole house audio and am looking at systems to power the speakers. I've been searching around through the forums and keep seeing references to 70v output coming from an amp. What exactly does that mean? I thought that wattage was what you dealt with when working with audio systems.

Can someone please explain this stuff to me? Also, what else I should know when dealing with a PA system including what is needed to get one up and running?

Thanks in advance!

[SteveD]

This may help

http://capitolsales.com/70Volttech.html

SteveD

[rocco]

Remember tube amplifiers? The final stage put out a pretty high voltage, and needed an output-matching transformer to allow it to put out 8 ohms. But then you had to wire your speakers (in combinations of parallel and series) to maintain the 8 ohm impedance. For PA systems, this was impractical.

So most PA amplifiers standardized on the output transformer putting out 70 volts, instead of 8 ohms. Each speaker would then have a separate matching transformer to change 70 volts to the impedance of the speaker, typically 8 ohms. If you pull a speaker out of the ceiling of your local department store (wait until no one is looking), you will find a little transformer mounted to the speaker.

The advantage of this system is that you can add as many speakers (including transformers) as you like, without worrying about maintaining impedance. As long as you don't exceed the output capability of the amplifier, the proper impedance is delivered to each speaker, and the volume is not affected by switching speakers in or out.

[digitalchaos]

Thanks you guys! You were both a big help! Steve, that was exatly the info I was looking for!

So, you can use a regular 8ohm speaker, but just need a transformer to make it work, huh?

What kind of transformer is needed? Is it something special or can you order it from, say, Digikey or Jameco? What is it exactly that I need to get? Also, wht kind of wire would you reccomend to run for the system? I don't think any point will be more than 50ft from the amp. I was planning on running shielded cat3 or cat5.

BTW rocco, yes I do remember tube amps, but I would never admit to it publicly. *feeling old* LOL

[huggy591]

Bogen, among others, still sells amps with 70V outputs for PA use. I believe they also have the speakers, transformers or baluns, and other components. See their site at www.bogen.com

[digitalchaos]

Well, I guess I ought to ask if there is a better way to do things beside a 70v PA system?

I am open to any suggestions since I am starting from scratch. Be in mind that I am kinda strapped for money.

[sponnath]

I got my 70v stuff from partsexpress.com and found it very reasonable. I did 70v as I felt it was the cheapest way to go. They sell amps and all.

[digitalchaos]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Steve P:
I got my 70v stuff from partsexpress.com and found it very reasonable. I did 70v as I felt it was the cheapest way to go. They sell amps and all. <HR></BLOCKQUOTE>

Thanks Steve! They do have good prices on the transformers and stuff. What is the quality of the sound coming from a 70v system? I do understand that you loose some sound quality as oppose to a 8ohm system, but I don't know how much though. I'd just hate to get all the stuff setup only to have it sound like crap!

Thanks again for the URL!