power line conditioners...

When I worked in high end audio, our guru placed a 120v-120v transformer (heavy duty -- 1000va) between the wall socket and the power amp in the system being auditioned. This was just before power line conditioners became available as audio system accessories.
I found a Sola 500va 120-120 transformer in the trash and tested it -- it worked. I tried it between the wall socket and my power amp. The sound stage opened up. Also, bass was tighter and more authoritative. I felt like the high end was also clearer. I am using a Dynaco st70 in triode mode driving Kef 102's, a dynaco PAS-3X, a VPI MK-IV turntable with an Alphason HRS-100 arm, various cartidges, and a Micromega Stage3 cd player. As my room is rather small, I don't feel the need for a sub-woofer now.
I wonder if any of you other members have any experience with PLC's, or Sola 120-120 transformers? And if you have any thoughts on why the sound is improved. Could it be simply reduction/elimination of voltage fluctuations coming from the wall, or are there other things happening like availability of stored energy in the transformer for musical peaks or transients?
Another question that I have is how are the audio-specific PLC's different than a 120-120 transformer? Are they different? Are they worth the extra money?
After hearing the differences that the Sola made, I am convinced that there is something to be gained from power line conditioning. I just don't understand it very well now, and would like to!

What bikes do you ride? I keep a Seven and Serrotta in my garage.

As for the power conditioners. First, no energy/power is stored in a transformer, so that isn't it. You likely are seeing the fact that you are now less influenced by interference in the line, but transformers can hummm so they aren't used in many (some do) power conditioners. A transformer also can't do anything to control or eliminate spikes or drops in the power, it will simply reproduce them on the output side.

Also when using a 500Volt-Amp transformer, you are limiting yourself to ~4 Amps of power @ 112 Volts, so I am surprised the bass is better and the dynamics too, but every system is different.

I live in florida and we have horrendous power here thanks to all the A/C's and such, so I have been using power products for years. I always liked the Chang Lightspeed units (TIP, I am selling these now) but once I tried the PurePower APC 700 I stopped using them, the PP's regenerate your electricity to perfect sine waves and have a battery backup so it can actually deliver more power instantaneously than the line itself, and keep you from suffering from power sags or surges. They aren't cheap, but they improved the sound so much in my system, I will likely never be without one or two again.
Well put questions. My intuition as an EE is that the improvements you noted revolve around the fact that you are using a very early preamp and amp (even if they have been modified/upgraded). I suspect your findings would be different with newer electronics.

I would think that although energy stored in the inductance of the transformer may be a factor, it is more likely that the transformer's most significant effects are due to filtering of high frequency hash that may be on the ac line (the filtering being provided by its limited bandwidth), and also to the ground isolation that it provides.

I suspect that your preamp and amp have less than ideal isolation between their chassis (which are probably used for signal ground) and ac neutral, due to component degradation that has occurred over time. That would have sonic effects that are hard to predict in both character and magnitude, but would almost certainly be negative. Likewise for the effects of incoming hash/noise/rfi on the ac line. The transformer very conceivably would help in both areas, but would have different and probably lesser effects with modern gear, due to the modern gear probably having components which are in better condition, as well as perhaps better overall power supply design, and components such as capacitors which are better quality to begin with.

I'm not experienced with plc's, but I've seen a lot of comments here from experienced people that with modern, quality, gear they usually do more harm than good. Not sure why that would be so. Most of them, I'd imagine, provide inductive and capacitive filtering of high frequency garbage, as well as isolation.

There are one or two very expensive models that actually convert the incoming ac to dc, then use the dc to power an ac oscillator and amplifier, thereby providing a really pure ac source. I have not seen any assessments of those units.

-- Al
BTW, I want to make sure that nothing in my previous post is construed as being pejorative of older tube gear. I've had several pieces of 1950's and 1960's gear in my main system over the years, and still do in the case of the fm tuner, and I have great respect for the sound quality they can provide if in good condition.

-- Al
Thanks for the replies! Very interesting information. And, it seems very reasonable about the hf hash being filtered out.

Kennyt, perhaps because the power supply in my st70 is the original the quad filtering cap is so far gone that filtering out garbage and fluctuations helps even with such limited current availability. I am currently modifying the ps with the SDS Labs power supply board.

By the way, I ride a 1981 Eddy Merckx with full Campagnolo Super Record. I sometimes swap the derailleurs out with Nuovo Record. I recently had it restored by Tom Kellogg in the Molteni paint scheme. He did a wonderful job on the bike! I do my own mechanics, and build my own wheels. Brazing in a new headtube was beyond my capabilities, so off it went to Mr. Kellogg.

Thank you, again, Kennyt and Al for your thoughtful replies!
A transformer also can't do anything to control or eliminate spikes or drops in the power, it will simply reproduce them on the output side.

Quite right that an iso tranny won't do anything for power sags, brownouts, dips or cuts. For that, you need an auxiliary source of juice. However an iso tranny offers excellent protection from spikes.

I've been using isolation transformers from Hammond, Deltec, Magnetek, Xentek and Topaz with digital sources, preamps and amps for five or six years now. The improvement the OP mentions is always there to a greater or lesser degree, depending on the quality of the gear, and even non-audiophiles can easily hear the difference. I even think that an isolator of proportional value should be part of the budget when you buy a digital player or transport. I have not heard a single player that did not benefit, up to my Esoteric P-10.

If you want more comments on the use of isolation transformers, look up posts in the archives by Sean and Lak.
The Equitech site has info on balanced transformers and MITs site has some papers on noise reduction.
An iso tranny also presents an inductive and capacitive load, when shielded, which should sound familiar with passive XO's. They can eliminate DC offset but aren't fond of it and can hum in protest.

The general rule of sizing, in our case, is that an iso tranny should be rated for double the maximum draw of the electronics to prevent saturation. They do not, or should not, provide ground isolation because, by code, the ground should be continuous. However, they do provide common mode (line to ground) filtration. Normal mode (line to neutral) noise is transferred through, to some degree, but most power supplies handle that in the rectifying process.

They are best used independantly as in one for CDP, one for preamp, etc. They are a defacto standard in hospitals and many industrial/laboratory applications where they prevent noise from going back into the line. Step-down transformers are common in all commercial buildings and have dual purpose.

The difference between toroidal and EI-core is mostly packaging. Toroids are less prone to mechanical hum but are not quite as effective as a filter.
My Panamax PC came with a small iso transformer. Very good results, and even the TV had a better picture, with none of the hash present from the untouched power line.
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I agree with Bob,They are quite amazing.i have Two Torus Pius
a 20a Balanced(components) and a 60a balanced(power amps).
they definately are Huge upgrade,
If your audio dealer will let you try one at home,
I'm sure you won't send her back.The music rides out with
authority,better bottom,no noise whatsoever.I think you would
very pleased with one.Speaking of bikes,this is the way I can describe the Torus.

You've been riding a honda 90 for quite some time and then
a friend lets you try out his Harley 1200,the power,control,
Authority.It been the best conditioner I have purchased yet
and have went with a couple of top names,but this leaves them in the dust.If I ever sell off any components,These won't be going,Totally,musically satisfied.
Don't worry, I thought there was nothing at all derogatory about your post.
I think that audio designers back then had a different philosophy and set of priorities in mind than those of today. The power supply of the st70 is simple and not very robustly designed. I think it uses a simple pi filter solely using capacitors and with not much capacitance at that; it seems not meant to handle much fluctuation coming from the outlet.
I am new to this web site and am really enjoying it! Thank you everyone for your replies! I am enjoying the education!