Question about 70V transformers

[katzenandguthrie]

Understood,that's what I've been doing. But if you were starting from scratch, what would be the determining factor in choosing 25v vs 70v? Line loss? Now just taking a guess, 25v is good for shorter total cable length and 70v is better for longer cable runs.

[Old Guy]

Hmm- I don't do a lot of this anymore Mark.

But think about it- the longer the distance they intend to send power, the higher they step it up.

High tension lines down to 440 down to 220 coming into your house.

So wouldn't it make sense that 100 v is going to allow longer cable runs?

25 volt isn't real common. So for me I would probably go with 70 or 100, lots of times when I do a new install I get the old stuff free for the hauling, so I would want what I could resell. That may or may not be an issue for you...

All factors being equal I would probably do the 100. I haven't looked at compnent cost, so I don't know that is equal. You pays yer money and...

[LICORNE]

.

That is correct it has to do with distance. For eample if I remember the telephone lines are 70 volt also. Most set ups are 70 volts. Amps with built in transformers are 70V also.

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[katzenandguthrie]

Most of the distributed type installs that I've run into have the 70v system. I seen a few smaller background music systems that have turned up some 25v. stuff. I was just looking to see if there as a general rule about when and where.

[Todd W. White]

Not sure if anyone's mentioned this yet, so here goes:

Many modern solid-state amplifiers are designed to operate a 70-volt line in direct-coupled mode (like Altec's 2280-series of Incremental Power Amplifiers). You might check your spec's - it could be that the amp will do so.

The less iron you pass the signal through, the better it will sound on the other end...

[Old Guy]

Originally posted by Todd W. White:
Not sure if anyone's mentioned this yet, so here goes:

Many modern solid-state amplifiers are designed to operate a 70-volt line in direct-coupled mode (like Altec's 2280-series of Incremental Power Amplifiers). You might check your spec's - it could be that the amp will do so.

The less iron you pass the signal through, the better it will sound on the other end...

<font size="2" face="Verdana, Helvetica, sans-serif">Todd is spot on that many amps will do it, they often have to be strapped mono.

But note- some areas, with tranformer coupling normal wiring can be used. Without an output transformer on the amp, it has to be in conduit.

Local regs vary- check before an expensive mistake. just to be in the safe side.

My grandpa taught me carpentry- his motto- measure twice, cut once.

[jdlowe13]

From my experience both QSC and Edcor make excellent transformers. I installed hundreds of both QSC and Edcor transformers in the Louisiana Superdome last summer. We used QSC CX-302 amps with QSC IT-42 output transformers to step up the output from 8 ohms to 100 volt and we used Edcor transformers at the speaker end to transform back to 8 ohms. Many wire runs are close to 1000 feet, some longer and some shorter. We did not have any problems with either the Edcor or QSC's. I recommend both.
They are probably all made by the same company anyway...
Hope this helps!

[Old Guy]

Originally posted by jdlowe13:
They are probably all made by the same company anyway...

<font size="2" face="Verdana, Helvetica, sans-serif">I would not bet against you.


FWIW, had some Yammie input trans that went to some guys here- they looked like peerless to me= I have opinions from several people including a former Yammie rep that they indeed were Peerless.

Opinions seem that about 75% of amp input trannies in the octal plug from the 70's- early 80's were Peerless. BGW is another that apparently was. They all copied Altec's standard- which shows what kind of player Altec was at the time..

[tomt]

For years and years and years, Altec had the BEST 70-volt transformers - the lowest insertion loss and core saturation around.

<font size="2" face="Verdana, Helvetica, sans-serif">speaking of which, do these seem somewhat $.high?

http://cgi.ebay.com/A-pair-of-Altec-...QQcmdZViewItem

[bfish]

$30 each, new, in 1975.

No further comment, my lawyer's skiing in Denmark...