Powerline Distortion & Power Factor Correction for Big Amps

For all these huge power sucking multichannel amplifiers the supply of choice seems to be a (typically toroidal) back-breaking line frequency transformer (or two), followed by a simple diode rectifier and huge storage caps. Pure 1960s technology. As any engineer knows, the resulting input current is nowhere near a sine wave, namely highly distorted pulses, and the output voltage is subject to line dips and sags. Much of the time the diodes are blocking and no power is taken from the powerline, hence the huge caps. In technical terms the power factor is much less than 1, typically 0.6 here. Think of it as 40% of the input power capability is wasted! On a 15A / 1800W house circuit only 1080 watts makes it into the amp, at 70% amplifier efficiency (see http://sound.westhost.com/efficiency.htm) you can get about 750 watts out of it - if you are lucky and the line doesn't sag any.

It's common in the electronics industry (and a European requirement for most electronic items) that high-powered devices be "power factor corrected" or otherwise changed to reduce input current distortion. Power is taken from the line for nearly 100% of the time, and filter capacitor size can be reduced some without affecting performance. With a 0.99 power factor you could get 1780 watts into an amplifier, and nearly 1250 watts out under the same conditions. That's a whopping 500 watts difference on the same 15A circuit!

So I ask, why don't sound purists insist on low distortion on the powerline input? And when will the US catch up with Europe and insist on low distortion powerline currents?

sounds like you should spread the word.

For reference the European requirement is EN 61000-3-2:2000 Electromagnetic compatibility (EMC) — Part 3-2: Limits — Limits for harmonic current emissions (equipment input current up to and including 16 A per phase).

A correction on power factor. Power factor has to do with the current and voltage fromthe wall being 'in-phase' with each other. In high power applications with an inductive load (like a toroidal transformer) the current and voltage become out of phase with each other thereby reducing the actual power available. For example (as RPL correctly points out) when you draw 10A at 120V from the wall, you would expect you get the full 1200W. In reality you get 1200VA and depending on the power factor, say .7, you would only get 70% of that or 840 Watts to use in your amplifier. Its a big waste.

The issue regarding the diodes is efficiency, not power factor, but the end result is the same, less power.

But in my experience with power factor correctors is they add distortion to the line, not reduce it. They try to draw current in phase with the volatge, in doing so causing current spikes. They do however correct the phase issue and get the power factor closer to 1.
The other piece of this puzzle is the type of supply that is converting the AC to DC. Here RPL is talking about a linear supply with series diodes, which is very inefficient in terms of converting power. A switching supply is much more efficient, but at the expense of noise.
My point of all this is there is much more to getting power, more importantly clean power, than just power factor.

maybe we should just build our own power plants in our houses...

Actually, I'd recommend putting it in the back yard rather than actually in the house - slightly less obtrusive...

What we need is a "Mr. Fusion" like on back to the future. Saves on space.
In all reality, the power fluctuates is so bad in my neighborhood that I'm considering putting in a very large isolation transformer (20KVA), just to keep out the spikes.

If you've got the $$$, there's always the option of getting something like a large APC Symmetra UPS and have an electrician integrate it into your main fuse panel so that everything in the house (except things like the A/C, refrigerator, etc) are protected.

I'm going to be building a new house next summer and am planning to have a 25KVA "whole house" UPS along with a rather substantial solar power/battery solution to help with our somewhat inept local power generation monopoly tripping over the power cord every time there's a storm. 8-)

A whole house UPS system seems like over kill to me. Typically UPS systems only give you "uninterupted power" for a short duration of time, until a secondary power supply can take over. They are used on critical systems. One of the benefits it does do is act as a filter and give you a clean sine wave for your equipment. Most of the power factor correction I have been exposed to is made up of a bank of capacitors. As the load becomes more inductive the more capacitors come on line causing the phase shift to lessen. Jim

Heh...audio buffs and overkill are like Bordeaux and cheese...they go so well together. 8-) A 25KVA ups would probably keep most homes lit up like an Xmas tree for quite a long time (again, the assumption is that you don't have things like your refrigerator or your central A/C on the ups)....probably at least an hour or two. And then if you want extended protection, it's relatively cheap to throw in a propane or diesel generator that kicks in when the UPS batteries are discharged more than X%.

Overkill? Probably. Expensive? For people that spend $10k+ on their stereo....probably not.

Cheers,