100V line systems?

[melody09]

Hello,
Is there a way to use low resistance output power amplifier (8-4ohm) like yorkville AP4040 to feed multiple long distant 100V line speakers??
The sollution is an autoformer 70v (1200w/4ohm) to 100v 1200va , a transformer or maybe a variac connected in reverse, can be a sollution for choosing the wattage of power amplifier I can use, according to the project requirements?

 

[JohnRoberts]

Hello,
Is there a way to use low resistance output power amplifier (8-4ohm) like yorkville AP4040 to feed multiple long distant 100V line speakers??

Yes, but. Professional instal system installers prefer floating transformer outputs because either output line can be accidentally grounded and the sound still works, saving them expensive service calls.

The sollution is an autoformer 70v (1200w/4ohm) to 100v 1200va , a transformer or maybe a variac connected in reverse, can be a sollution for choosing the wattage of power amplifier I can use, according to the project requirements?

Back when Peavey started making Install gear (several decades ago) we tried to sell amps using autoformers instead of true transformers to reduce cost and the industry rejected that approach, insisting on true output transformers.

JR

 

[abbey road d enfer]

A variac would probably suffer of high distortion and poor frequency response.
They are oprimized for 50/60Hz, not for the audio range.
BTW, many 100V systems use standard amplifiers.
An amp capable of 1200W into 8ohms is capable of delivering 100Vrms.
However, for moderate power, step-up transformers are a preferred solution.
You have to understand that the power rating of 100V components is a rough guide. Don't sweat it too much.
An amp that delivers 80W to a 100V line is only 1dB quieter than a true 100Watter.
I know many places that run their "constant voltage" system so quiet that they could have divided the power requirement by a factor 2.
If you run a 100V/100W speaker on a 70V line, it just runs at half-power (-3dB)
Most 70V systems today use standard (low-Z) amps.

 

[JohnRoberts]

A variac would probably suffer of high distortion and poor frequency response.

+1... Peavey used to sell an accessory step-up/down "audio" power transformer called "Automatch" but it was only 400W.

Most 70V systems today use standard (low-Z) amps.

I have been out of the fixed install business trenches for a while, but back when I was still in the game transformer isolated outputs were standard.

JR

 

[melody09]

I know about Peavey automatch II that traded as autotransformer but in photo there are 2 coils there was options for 400-200-100W to 100/70V only.

If it was for fixed installation an already 100V out with transformer inside or transformless amp would be a sollution but what about portable systems (rentals) that the amp wattage (and the speakers quatity) depents to the application.

Is there a sollution for this problem so anyone can use the low z power amp need each time?

Do you think standard psu transoformers like 230V to 110V for example can work for 500W/4Ohm or 300/8ohm to 100V?
Or the problem is the same like variacs?
Anyone tried this?

There are many small chinese 100V transformers in crap speakers and to be honest I think these transformers are not different from common psu transformers or have any optimisation for audio range. Yes a well known brand have to do it. Like Peavey have a freq responce diagram in spec sheet.

I don't know if it is just theoretical and marketing more than real world transformer or autotransformer construction difference.

 

[JohnRoberts]

I am repeating myself but professionals in that market frown upon direct coupled and auto-formers, or at least they did.

The Peavey "automatch" was a very old accessory product used for sundry tasks, not specifically targeting constant voltage market. I only listed it because it was a proper "audio" power transformer. It used to be cheap, probably not still.

Indeed most fixed instal power amps use a conventional low Z audio amp, connected through an output transformer to deliver 100V/70V/50V/25V/etc.

Cheap audio output transformers may lack the magnetic core(?) to cleanly reproduce loud, low frequency bass. A definite cost tradeoff faced by manufacturers servicing this market.

JR

 

[abbey road d enfer]

I have been out of the fixed install business trenches for a while, but back when I was still in the game transformer isolated outputs were standard.

I don't know about the situation in the US, but in Europe, non-floating "constant-voltage" outputs are quite common.

 

[abbey road d enfer]

Do you think standard psu transoformers like 230V to 110V for example can work for 500W/4Ohm or 300/8ohm to 100V?

PSU xfmrs have the same issues as variac, i.e. poor coupling, which results in HF losses.
Have you actually checked the available products? They are not much more expensive than power xfmrs. And versatile enough. Many offer different input taps and dual 70V/100V secondaries.

I don't know if it is just theoretical and marketing more than real world transformer or autotransformer construction difference.

There are indeed differences in construction, but they don't necessary imply higher cost.

 

[moamps]

I don't know about the situation in the US, but in Europe, non-floating "constant-voltage" outputs are quite common.

In my country which is in Europe, 100V systems are balanced using transformers.

At the time I was involved, toroidal power transformers worked quite well for that role.

 

[melody09]

I understand all of your replies.
Just asking if someone tried an other type transformer, an other way and it worked for him.
That is the point.

There is also another question if a step down transformer (speaker side) can work as step up also (reverse wired).

There many people saying that can be used as the transformer don't have input and output and many other tells that it is not possible as it is very critical if the input is connected to the primary coil or the secondary...

 

[JohnRoberts]

In my country which is in Europe, 100V systems are balanced using transformers.

At the time I was involved, toroidal power transformers worked quite well for that role.

I was involved with designing many fixed instal mixer-amps ranging from 5W up to hundred of watts. My mixer amps were designed to be cost effective so we used mostly EI core output transformers but they were sized to pass reasonable (not audiophile) bandwidth.

There is also another question if a step down transformer (speaker side) can work as step up also (reverse wired).

yes... transformers just transform either way, but keep in mind that they are only rated for modest power.

JR

 

[abbey road d enfer]

In my country which is in Europe, 100V systems are balanced using transformers.

Is it mandatory, or just some kind of "tradition"?
Here we have many systems based on bridged amps. Of course safety constraints resulting from the "low-voltage directive" must be obeyed., basiscally the same than any mains power distribution system.