Audio output transformer

"klem kedidelhopper"

** The Technics amp will probably blow up.

You cannot use 70V line *step up* trannies with domestic hi-fi amps.

Line voltage power amplifiers are specially designed to drive the included step up transformer - which presents a lethal load to most SS amplifiers.

BTW

"Technics mono 100W amp" leads to no particular model on Google.

So what the f*ck have you really got ??

.... Phil

Klem-

You may be able to do what you want, but selling it makes you liable if anything catches fire!

Suppose you connect your 100 Watt Technics amp directly to the distribution system. Maximum RMS voltage out of a 16 Ohm output would be 40 Volts. For a 70.7 Volt system, maximum power would be somewhat less than 100 Watts before it starts to clip.

Using a 100 Watt (or 60 Watt) constant voltage transformer connected backwards to the amp may work for your purposes, but there might be a penalty in frequency response. Try it and see how it sounds.

About forty years ago I did something similar with an amplifier and some constant voltage transformers. It was a jury-rigged background music system using an old Eico FM tuner and Heathkit monaural tube-type HiFi amplifier. Speakers were mounted in cardboard boxes. It worked and sounded quite well, considering!

Fred

"Fred McKenzie"

** The most sensible thing to do is use with a domestic stereo amp is use it in bridge mode AVOIDING the step-up tranny entirely.

This way, you will easily enough get 70V rms and with very little chance of damaging the amp as the resistance in the distributed speaker system plus cabling is likely to be more than 8 ohms.

A simple ohm meter check will confirm this and if it is a tad less than 8 ohms, just add some ohms in series.

.... Phil

"Jeff Urbane is a PITA f****it "

** They ARE close relatives you know .....

Obviously any words of wisdom as wasted on this anencephalic oxygen thief.

For the curious:

The 8 ohms of resistance alluded to by me is in SERIES with any reactive/ inductive or saturating line transformer & speaker load as seen by the bridge mode amplifier.

Soooo, no matter what the drive level or frequency, the resulting load Z cannot drop below that number.

.... Phil

You might be right... And I'd certainly be cautious about using a constant-voltage transformer with an amp not specifically designed for it. But I suspect you don't understand how a transformer works -- that is, how it transforms impedances.

Let's say a transformer is rated a 4 ohms to, oh, 1600 ohms. One side //does not// have an impedance of 4 ohms, or the other side 1600 ohms. Rather, the transformer has a turns ratio of 1:20, which produces a impedance transformation of the square of the ratio, or 1:400.

The transformer would work in //any// application where this impedance ratio was needed, whatever the specific impedances were -- for example, 100 to

40000 ohms. (I'm ignoring considerations such as primary inductance, leakage, etc. The principle is the same.)

That assumes the "some low frequency" gets through to the transformer.

I remember J Gordon Holt's review -- almost 50 years ago -- of the KLH Nine electrostatic speaker. He pointed out much the same thing, suggesting that a Really Big capacitor in series with the speaker's input (which is a transformer, as you know) when driving it with a transistor amplifier might be a good idea.

By the way, core saturation from an AC current doesn't cause the inductance's impedance to "disappear" -- it just reduces it.

Lenny, the biggest difference in the amplifers is that a PA amp is designed to be used 24/7/365.25. The transformer adds isolation from the amplifer, as well. I see no problem, as long as you're willing to stand behind what you sell and tell them that the transformer was added to match the speaker wiring. MCM sells transformers for this application. We did it back in the '70s to clean up installations done by knowitalls, and their victims didn't want to pay for another amplifier.

As far as matching constant voltage speaker system impedance, keep these numbers in mind:

70V = 5000/W which means your 100 W amp would be 50.00 Ohms. 25V = 625/W which means your 100 W amp would be 6.25 Ohms. 100W is in the ballpark of what I would specify for a 60W load, if you beleive that there will be more speakers installed at later date. It could drive up to 120W load, in most installations with no problems.

--
You can't have a sense of humor, if you have no sense.

f

speakers installed at later date.

Well as it turns out, (and Phil was correct), so call me an oxygen thief, f****it or whatever else suits your fancy Phil, in that the amp is not a mono amp but a 100 Watt per channel stereo amp. So now I don't want to use this amp for this application. This has all been an interesting exercise but unfortunately I have now run out of amps so I may very well have to buy a 60watt paging amp. Lenny