I was hoping to get some input on using a 70 volt amplifier to run a set of outdoor speakers (Niles OS20's) about 200 feet from the equipment. What is the consensus on sound quality using a transformer on decent quality 8 ohm speakers?

The bigger the transformer, the better the bass. That will probably be the consensus there.

But why are you considering using a 70 volt amp to run one pair of speakers? The point of 70 volt is to create a system where individual speakers can tap off the amount of power appropriate to their location, where the total tapped off does not exceed the total available. This is very much like high voltage power transformer distribution across the city -- each 110-0-110 transformer is designed to take a certain amount of power from the higher voltage local grid.

I see ONE benefit to using a 70 volt amp for one pair of speakers: either you can use thinner wire or you can run it further. Or maybe you can combine those two ideas and run some slightly thinner wire a bit further than you would, say, 14 or 12 gauge wire.

By the way, the set of Mariner 100s that I installed with about fifty feet between the amp and the volume control, and 200 feet between the VC and the speakers, sounded AWESOME. I used 14 gauge wire and about 100 w/channel.

I would wonder the same thing. Why use a 70 volt system for a single pair of speakers when yopu can do it in 8 ohm. 70 volt is great for running lots of speakers in parralel over long distances,, higher voltage, lower current loss, and yes wire guage is a benefit. But unless you use top notch transformers, you will be compromising on fidelity, and SPL capability. In a middle of the road 70 volt transformer, insertion loss at certain frequencies becomes an issue due to the transformer. More power doesn't fix it either. As soon as the core saturates, the transformers capacity for allowing more energy to be transmitted maxes out. typical 70 volt systems tend to be limited in frequency response. I use them all the time for paging and low level background music applications. I wouldn't use 70 volt in your situation

While I tend to agree that 70 volt may not be the way to go for the intended application I think the fidelity issue is over stated. I have heard some VERY good 70 volt systems. It's not that hard to find a decent transformer. Stick with Atlas and you will have very respectable frequency response. Combine it with some nice QSC 70 volt amplifiers and you can get very good fidelity out of 70 Volt.

I would also contend that 70 Volt has as much to do with controlling costs as it does to do with the "wattage per location" issue. If you have to run a few thousand feet of wire it is a heck of a lot cheaper and easier to run 20 gauge than the 8 gauge or so that you would need for a 8 ohm load.

Keep in mind that 100 watts works out to about 25 Volts. Meaning you can use 25 Volt volume controls and transformers on a 100 watt amp for with good results.

It seems to me that you have a choice though. If you have a 70 volt amplifier that you are trying to make use of then buy a set of Atlas outdoor cabinet speakers to go with the amp. They sound better than the Niles do anyway. Or use a regular 8 ohm amplifier with at least a 14 ga. wire. If you allready have both then just get a high wattage 70 Volt Atlas step down transformer to put at the speakers.

Ted , yes,, QSC, and Crown both make some high quality 70 volt amplifiers, and as long as you stick to high quality transformers with high permeability cores, the fidelity isn't bad at all. I just think in this residential situation, it's so muh easier to use an 8 ohm system. I think the main concern was insertion loss over distance. it's pretty minimal if you use 14 or even 16 G wire, and you can compensate for loss with higher power.

Let us not forget that tube amplifiers use output transformers, and plenty of people still consider them the best fidelity available.

Larry
www.fineelectricco.com

16ga on a 200' run to an 8 ohm load is about a 1.6 dB insertion loss with a damping factor of 5. You have to go with a 10ga wire to have an acceptable loss of .5 db and damping factor of 20. If any portion of the speaker drops closer to 4 ohm the loss on 16ga is a full 3 dB and the damping factor is 2. I assure you this setup is audibly BAD and not great for the amplifier either.
On a 70 volt line 200' is nothing. Of course if an impedance matching VC is placed at the speakers then the equation changes again. We simply don't have enough info on the actual setup to say for sure. the moral of the story is that you SHOULD be using 70 volt line on some of these large properties with lots of outdoors speakers that are all on the same zone.

A decent amp has no problem dealing with damping factor, and a loss of 3db isn't the end of the world either. As for fidelity, I have done a lot of 70 volt, and used a wide range of transformers both integrated (JBL contractor series) and custom retrofitted systems. We have done many large venues using a mix of distributed 70 volt, and distributed / delayed 8 ohm systems. We never use 70 volt in the main spectator areas, bowl, gymnasium, or any room that requires higher SPL. in subbordinate areas such as a concourse, public areas, dressing rooms, foyer, we usually use distributed 70 volt. In the main spectator areas, often times the amplifier racks are over 200 feet away from some of the loudspeakers. Insertion loss is a reality, and with appropriate power, and conductors, it's not an issue that's even relevant at the end of the day. Adding 70 volt transformers also increases costs, and the chance of a failure since there are more connection points in the system. The biggest problem with 70 volt in many scenarios is SPL capability. The lower the sensitivity of the speaker you are using, the more this becomes a problem. ordinary ceiling speakers designed for use with 70 volt transformers are extremely efficient for this reason, as are paging horns. In order to achieve the kind of fidelity Ted is talking about you will have to use a transformer that will probably be too large to fit inside the OS20. I have retrofitted copies of the OS20 with inexpensive 70 volt transformers , and there was little room to spare. If you are determined to do 70 volt on the patio, consider a JBL C25T, it's only a little larger, and although not as Hi Fi sounding, will probably last longer outdoors and is ready to go right out of the box.

Incidentally, the OS20 is rated @ 8ohms. add 200 feet of 16 G wire and that number is going to increase to around 9 ohms. So I don't see the amplifier ever seeing anything less than 8 ohms unless something happens to the speaker or the line.

As for vacuum tube amps. I think that is a subjective thing. SImilar to vinyl recordings vs CD. Is the absence of noise and distortion percieved as somehow lacking, or is it the other way around? Broadcast and recording went full circle in some regards. about 12 years ago, there was a huge metamorphisis back to analog tape using Dolby SR noise reduction. I think that trend has subsided now, especially with the proliferation of basement digital recording studios some of which can produce results at par with the professional houses. but tube devices such as tube microphone preamps, signal processors and other ancilliary equipment have become standard tools in most professional recording studios so there has to be a reason for it since these devices typically cost a lot more than their chip based counterparts. As for a good quality 70 volt transformer sounding better in the loop. I can't see how another conversion of the signal would improve fidelity. JMHO