[kelly]

A while back, I got into a little trouble by saying something to the effect of noticing that the HD600 seemed to behave better on amps that had larger PSUs. I didn't have any logical reasoning for this and perhaps the correlation is completely coincidental.

But...

I've noticed that as you spend more money on amps, the size and output of the transformers seems to go up. You and I know that headphones simply don't need much power to get to their maximum volume even with plenty of headroom. So what's the deal, then? Why do some of these headphone amps have the large toroidal transformers? Why not use a smaller transformer if there isn't an actual difference in sound quality? On the other hand, if there IS a difference in sound quality, WHY?

To me, this as illogical as saying that a glass of lemonade from a 25 gallon drum tastes better than a glass of lemonade from a 2 quart pitcher. If you only need a glass full anyway, how does having all that extra lemonade make your glassful taste better?

 

[Pace]

Maybe the powersupply creates less interference when it doesn't have to work at full load...

Just my two (euro)cents.

 

[sacd lover]

Kelly, I might have an answer. I remember reading an article by Paul McGowan of PS Audio discussing the importance of power supplies; and he noted how a larger power supply improves the sound even in low power draw components. He THEORIZED that the larger power supply has a lower impedence itself. This makes the power supply less susceptible to any number of powerline anomolies and the lower impedence can supply more current into the component. I am going from memory of something I read along time ago, so I may not have this just right.

 

[AndreYew]

Kelly,

There are lots of possibilities, and it's difficult to devise a good experiment to isolate out the possibilities.

1. Marketing. People expect bigger PSUs.

2. Different secondary effects, not necessarily related to the higher current delivery of a bigger PSU. For example, bigger PSUs tend to have bigger transformers and capacitors. Bigger caps alter the input impedance of the power supply, and this can affect how noise on the power line is injected and filtered into the system. Same thing with bigger transformers --- different impedances, parasitics, and therefore different resonances.

3. Bigger power supplies require more space, and that can alter how its non-galvanic radiation (eg. its effects on the circuit through the air, rather than through its direct connection to the circuit) affects the circuit, because the power supply's physical configuration is different. The rectifiers in a power supply can emit a lot of RF because rectification produces sharp edges. This is why some people use hyperfast, soft-recovery diodes and snubbers for rectifiers. RF fields can die off very quickly, so perhaps moving a power supply away by a little bit can have a large effect, especially if the noise occurs in an especially sensitive hearing region. Lots of audiophile equipment have separate power supplies to isolate the PSU.

4. Related to 2 and 3, the radiation properties of a power supply can change with the different components that make up a power supply as well, because of different resonances and parasitics.

One measure of a circuit is called the Power Supply Rejection Ratio (PSRR), which is a measure of how indifferent a circuit is to its power supplies. This is why some people obsess over different current sources for their circuits. One could argue that a badly-designed circuit has bad PSRR, and therefore depends on a heroic power supply as a crutch to perform well.

--Andre

 

[kelly]

Thanks for the replies so far. I want to address the one about marketing. I considered this possibility myself (that people just like bigger numbers in the specs of things they pay more money for) but have found too many hobbyists, DIYers, modders and engineers who use larger PSUs to believe their motivation is so simple. I don't think all of them are simply succoming to a false quality standard set forth by large commercial companies--after all, no DIYer is concerned with THD measurements.

 

[sacd lover]

Kelly, go to PS Audios website and find PAUL McGowans article where Sterophile interviewed him. Thats the article I was thinking about. The secondary impedence of a larger transformer is what seems to make such a big difference. The article gives reasonable explanations to your question.

 

[kelly]

sacd lover
I looked on the site but couldn't find it. If you see it again, post a link.
Thanks.

 

[sacd lover]

Kelly, go to the PS Audio website, click on new/reviews at the top. This will get you to a list of reviews. The review you want is titled: The Stereophile Interview With Paul. I dont know how to do a link or I would have.

 

[HD-5000]

kelly, I have an answer. Usually, big psu's in low gain devices is more often a higher quality design.

 

[AndreYew]

Here's a link to the Paul McGowan interview in Stereophile:

http://www.stereophile.com/showarchives.cgi?222

Lots of assertions, but very little real technical meat.

--Andre

 

[Gord SW Ont]

I'm no expert ... but I thought part of the problem is that the power requirements for the peaks (high power needed for very short time frames) were "much" higher than the power draw to give normal volume for the major portion of the music.

It may be that you can never really have enough headroom for these dynamic peaks which often provide the realism in music. So the bigger the power supply in the higher priced units often translates into better, more realistic music???

Well at least it's a theory ;^) ... Gord.

 

[DarkWolf]

Drawing on my experience with computers rather than with audio equipment, since the former far exeeds the later, bigger PSUs have a number of advantages, several of them have been metoned here already. One of the reasons people buy bigger PSUs than they need to for computers is that a bigger one will generate less heat putting out the same ammount of power as a smaller one. People looking for extremely quiet and/or more exotic cooling methods often opt for a huge PSU even in a light weight system so that it won't need much cooling. By huge I'm talking about PSU's topping 400 or 500 watts where you could probably get by on 250 or 300 watts. (Some people have even made water cooled PSUs.. I sure wouldn't though.)
In audio equipment I would think that it would make sence to have the PSU running cooler for several reasons. Lower interference and higher consistency seem likely to me. It should also last longer than an smaller PSU of similar quality.