Will this isolation transformer limit power draw?

El: Here's a few responses to your questions:

1. If a transformer removes "grunge" (that must be some technical term that I am unfamiliar with) why doesn't the transformer that is already in the audio equipment do the job?

Transformers do remove AC noise to some extent, but not to the level that a good quality low capacitance isolation transformer can. As mentioned in another thread pertaining to various transformer designs, some transformers are FAR more efficient at this than others. Obviously, there are different designs for different applications.

2. Why doesn't power supply capacitance do the job? If this is a real problem, a PS filter using a series inductor between capacitors would be a lot cheaper than a transformer.

Both comments are somewhat valid. Large quantities of capacitance in the power supply can and does act like a filter to some extent. Then again, RFI can "ride on top of" DC, so filter capacitance doesn't solve all of our problems.

An inductor in series with the PS can provide many of the benefits of an isolation transformer. Only problem is that the inductor produces yet another high intensity EM field inside of the component, probably won't pass as much current and won't be quite as effective in terms of total noise reduction. It could be a step in the right direction, but may also have some drawbacks that would require careful attention to detail. Making the higher efficiency noise filter external to the device removes the complication and has other benefits to it.

3. Why does the AC power need to be "grunge" - free? Low powered amps can use the applied audio signal as their source of power.

Please clarify this one. What i got out of this is that the signal being applied to the amplifier would actually become the source of power for the amplifier itself. If that is what you are implying, such a design is fraught with problems to say the least.

4. Of the many people who have bought power conditoning equipment, how many had measurements of their AC power to determine if they had any "grunge" to worry about?

Couldn't tell you any of the specifics. I can tell you that i have "looked at" and "listened to" what is being fed to us via the AC lines and it is FAR from being a "spectrally clean" 60 Hz waveform.

sean...Thanks for the straightforward answers. I could respond with follow up questions, but I doubt that we would ever agree completely.

My concern (probably too strong a word) is that many audiophiles spend a lot of money on things that have no (or very little) benefit because they have no engineering knowledge and are easily misled by half-baked pseudo-scientific smoke and mirrors.

About the audio amp that is powered by the audio signal, I can't remember exactly where I came across this: it would obviously be some unique situation, perhaps an impedance matching matter. Of course, electrostatic headphones use the audio signal to generate their high voltage bias. In my previous incarnation as an aerospace engineer we used a square wave instead of a sine wave for ac input power. It's more efficient, and the dc comes out the same.

El: an amp that derives its power source from the audio signal would be lower in linearity than a Class C amplifier. The end result would be that gobs of resolution would be lost. After all, rather than pass all of the signal onto the gain stage for further amplification, some of that signal would be absorbed and converted into drive for the power supply.

Other than that, your "concerns" are quite valid. If "audiophiles" would concentrate on the basic fundamentals of proper gear selection and installation, many of the "gadgets" being offered become inconsequential to achieving excellent results. I've seen WAY too many systems that were loaded down with expensive "tweaks" and achieving less than optimum performance simply because the basics of proper installation were being ignored or looked over. When one selects gear that is less than well designed and impliments it in poor fashion in their listening environment, subtle changes ( tweaks ) to the system help to band-aid all of the wounds that were previously wide open and exposed. When one adds up all the expenses of the "tweaks" that they spent taking this approach, they could probably have purchased better gear that was less susceptable to "tweaking" to begin with.

Given that most gear made today suffers from phenomenally under-designed power supplies though, and the AC signal that we are being provided with in most major metropolitan areas is so bad, i don't consider the PROPER filtering of AC to be a tweak. It is almost mandatory. That is, if one really wants to hear what their system is capable of, well set-up or not. Like anything else though, there are various products and designs available to attempt the proper filtration of a signal. Some are far more effective and / or deleterious to the results that one can achieve. Sean
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Sean...Using an audio program instead of 60 Hz for power is obviously an extreme case.

Isn't it true that the diodes of the power supply only conduct during time intervals when the input 60 Hz voltage is greater than the rail voltage. Most of the time the diodes are not conducting, and the amp "coasts" on what is stored in the PS capacitors. When the amp is under no load, the PS capacitors will charge up to the 60 Hz peak voltage, and the diodes will just be delivering very brief pulses to keep them charged. So, if the power supply has pulses for input, why does the exact shape of the original waveform matter?

In the good old days, an outboard "bank" of capacitors was a popular mod...simple and effective. I believe it would do more good than a transformer.

An outboard bank of caps is FAR less effective than capacitors placed as close as possible to the output devices. That is, as far as storage devices go and minimizing sag on the rails.

As far as the 60 Hz voltage vs the rail voltage goes, the 60 Hz voltage will always be higher than the rails in most conventional designs. If one were using only partial rectification and not a bridge, the charging rate would be far more cyclical. As it is, the cycling with the resultant "glitching" that occurs during a typical charge rate has to do with the diodes themselves turning off and on, which produces ringing and distortion. This can be seen in many amps as a 120 Hz and sometimes even a 180 Hz resonance. This is why many designers are switching over to diodes that recover more quickly as they produce less noise.

Other than that, believe me, a good iso transformer will do GOBS more for you than a bank of caps could in terms of the filtering of noise. Having said that, i am a BIG fan of large capacitor reserves within the component itself, especially in power amps. That's why i've purchased BIG electrolytic cans by the box-full. Sean
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