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.

 

[moamps]

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.

It is not required, but it is considered good and reliable engineering. In practice, it has been shown that systems with an output transformer are less susceptible to electrical failures, and are less sensitive to temporary short circuits that occur on long lengths of 100V PA systems. Also, a balanced signal is used to reduce as much as possible interference with other signals (fire alarm signals, etc.). The quality is satisfactory because mostly the most important thing is to transmit speech information, music playback does not require HIFI.
In any case, I would suggest to the OP to use several smaller transformers connected to one output of the amplifier if there are several incoming 100V lines and not one large transformer, and to try using toroidal transformers with a ratio of 1:1 (115-115V). 1.2kW on 4 ohms is approx. 70V.

 

[JohnRoberts]

It is not required, but it is considered good and reliable engineering. In practice, it has been shown that systems with an output transformer are less susceptible to electrical failures, and are less sensitive to temporary short circuits that occur on long lengths of 100V PA systems. Also, a balanced signal is used to reduce as much as possible interference with other signals (fire alarm signals, etc.). The quality is satisfactory because mostly the most important thing is to transmit speech information, music playback does not require HIFI.

yes... In my experience the professional background music installers were pretty conservative and resistant to change (even if cheaper). The ability of floating audio outputs to survive inadvertent grounding saved many service calls. In the low margin fixed install business one service call can wipe out an entire project's profit margin.

[TMI] Peavey had difficulty breaking into the fixed install business who were happy to not fix what wasn't broken (they were very happy to buy Japanese made Toa). It was only after Peavey introduced MediaMatrix the massively computerized sound system controllers that the conservative establishment of installers could no longer dismiss Peavey because one MediaMatrix computer could replace a room full of rack gear and miles of wire. If they ignored the cost savings and labor reduction, they would lose the job to somebody who embraced the change, and won the bid with lower cost (/ TMI).

JR

In any case, I would suggest to the OP to use several smaller transformers connected to one output of the amplifier if there are several incoming 100V lines and not one large transformer, and to try using toroidal transformers with a ratio of 1:1 (115-115V). 1.2kW on 4 ohms is approx. 70V.

 

[abbey road d enfer]

Different countries, different habits. When I was still in business, my customers gladly embraced transformerless amps, particularly the Powersoft install amps.
Indeed, the max output was nearer 80V than 100 (*), but after all it's only a 2dB difference. Considering most of distributed systems are running far from their limits, it's never been an issue.

(*) Which made them perfect for 70V distribution. Some installers or customers were reticent using 70V distro, because the european standard is 100V. However, when given the possibility to discuss the pros and cons, in most cases 70V won.
Failures due to short-circuit have never been a recurrent issue (these Powersoft amps are extremely well designed).
Being used in bridged mode, there is no more interference than with a xfmr output.

 

[Brian Roth]

All this 70V (100V) conversation brings back memories. I was a nerd kid and read everything I could re. electronics. I also received four hobbyist magazines per month (Popular Electronics, Electronics Illustrated, Radio-Electronics, Electronics Experimenter). Somewhere I read an article about series-parallel speaker wiring so you could "match to the correct" output terminals on your amp.

Around that time I recall checking out the ceiling speakers in stores Mom shopped at. Some newer stores had drop-tile ceilings with speakers behind cover plates dotted all over the ceiling space. I figured that wiring must be a crazy mess of series-parallel.

Maybe 5 years later I took a summer job in High Screwel right after I could drive in 1970. It was at a small local contractor that did commercial jobs: frisbee speakers in the ceiling, horns in the warehouse and outside, etc. I asked the gruff (yet kinda nice) owner how all that was physically wired to "match the Ohms" with that many speakers spread everywhere.

He looked at me: "Ohms? What's that? We wire up by Watts!" and showed me a sample speaker with a transformer mounted on the rear. "See? Them two wires are marked 70 Volt and that's where the wires connect to the amplifier. All them others are marked in Watts and two connect to the speaker, and it has Ohms. All them Watts add up to be less than the Watts of the amp." Paraphrasing him, but close enough.

I was confused. We were "randomly" jumping between Ohms, Volts, Watts in a speaker wiring system. I kept my mouth shut so he wouldn't think I was a moron. Learned to be a monkey scurrying up/down ladders and twisting wires together with wirenuts with my head poked into the ceiling (or 20 feet up in the warehouse).

It took me a bit of time to puzzle out the math. Bridging loads should have been obvious to me (like AC mains systems) but I was all self-taught. Of course, later I learned you could make SPL tweaks by changing speaker taps.

All I really needed to know as an installer was "them Watts" because "We don't need no steekin' Ohms!" <g>

Alas...my 70V ladder-monkey days are LONG past!

I just pulled out an old 70V xfmer from a junkbox here. Two wires marked 70V, the others Common, 10W, 5W, 2.5W. 1.25W and .625W.

Bri

 

[JohnRoberts]

All this 70V (100V) conversation brings back memories. I was a nerd kid and read everything I could re. electronics. I also received four hobbyist magazines per month (Popular Electronics, Electronics Illustrated, Radio-Electronics, Electronics Experimenter). Somewhere I read an article about series-parallel speaker wiring so you could "match to the correct" output terminals on your amp.

Around that time I recall checking out the ceiling speakers in stores Mom shopped at. Some newer stores had drop-tile ceilings with speakers behind cover plates dotted all over the ceiling space. I figured that wiring must be a crazy mess of series-parallel.

Maybe 5 years later I took a summer job in High Screwel right after I could drive in 1970. It was at a small local contractor that did commercial jobs: frisbee speakers in the ceiling, horns in the warehouse and outside, etc. I asked the gruff (yet kinda nice) owner how all that was physically wired to "match the Ohms" with that many speakers spread everywhere.

He looked at me: "Ohms? What's that? We wire up by Watts!" and showed me a sample speaker with a transformer mounted on the rear. "See? Them two wires are marked 70 Volt and that's where the wires connect to the amplifier. All them others are marked in Watts and two connect to the speaker, and it has Ohms. All them Watts add up to be less than the Watts of the amp." Paraphrasing him, but close enough.

I was confused. We were "randomly" jumping between Ohms, Volts, Watts in a speaker wiring system. I kept my mouth shut so he wouldn't think I was a moron. Learned to be a monkey scurrying up/down ladders and twisting wires together with wirenuts with my head poked into the ceiling (or 20 feet up in the warehouse).

It took me a bit of time to puzzle out the math. Bridging loads should have been obvious to me (like AC mains systems) but I was all self-taught. Of course, later I learned you could make SPL tweaks by changing speaker taps.

All I really needed to know as an installer was "them Watts" because "We don't need no steekin' Ohms!" <g>

Alas...my 70V ladder-monkey days are LONG past!

I just pulled out an old 70V xfmer from a junkbox here. Two wires marked 70V, the others Common, 10W, 5W, 2.5W. 1.25W and .625W.

Bri

"Constant Voltage" system math is much simplified. The audio voltage is not really constant but it is normalized for 70V/100V so systems can be assembled/designed based on adding the wattage of all the sundry loads together. The rule of thumb is to power the system with 10% or 20% more amplifier watts than the total of all the loads combined, just to be safe.

JR