Why do I need power management if I have a great power cord?

Here is the latest video from Amir on power cords.

This statement is false. Amirm is testing a particular cable- an Audioquest, not all power cords. It would be correct to say 'Here is the latest video from Amir on an Audiquest power cord'.

However, there is a flaw in his testing regime, which is that all power cords obey Ohm's Law; the conditions he set up for testing did not have a great power draw on the cable. As a result, negligible voltage drop across the cord and quite naturally: negligible results.

The benefit of a good power cord IOW has to do with the current drawn through the cord which won't happen with lower powered equipment (for example, an Audio Precision tester).

Power cords that can make a difference don't have to be expensive however! I agree with Amirm that $5,000 should only be spent if it makes you feel better somehow... IMO/IME there's not much use in messing with power cords unless you have equipment that draws enough power to result in a substantial voltage drop across the cord.

I've seen a power cord result in a loss of 40 Watts at full power from one of our amps (the MA-1). That's a pretty measurable result! But the MA-1 draws a bit of power, being a 140 Watt class A triode amplifier.

Put another way, if you want to get the most out of some amplifiers a power cord can really help, and with other amps maybe not at all. The power that the amp draws from the wall plays an enormous role in this which cannot be ignored as we see Amirm doing in this video.

To atmasphere: I’m puzzled by your comment that this Nelson Pass quoted 48 Amps is “how much current is present when the power supply of the amp is shorted. It’s available to the output section in the form of charged capacitance. This is used to help reduce IMD in the output section and is not something that the output section can pass to the loudspeaker.” Perhaps I failed to see what you did there; but I thought that the extended time that my tube amp can drive my speakers from the source when I turn the tube amp off (while the source is still playing) was, in fact, the capacitors discharging through the speakers.

I thought it was funny to use the word 'pass' when talking about a Pass Labs amp...

At any rate, all that extra capacitance used in so many amps is there to reduce IMD at high volumes (so the amp will sound smoother). The amp isn't going to be able to make any more power since the voltage in the power supply plays a direct role in that- to make more current you'll need more voltage. All the excess capacity does is prevent the voltage from sagging over a short period of time when the amp is making higher amounts of power.

Many solid state amps have response to DC. This means that the low frequency timing constants in the amplifier go lower than that of the power supply (unless its a battery)- thus low frequency noise can cause the amplifier to modulate its power supply. When this happens, IMD increases. This can be avoided by having enough feedback in the amplifier circuit, allowing it to reject power supply noise, but that amount of feedback is a rather large value (+35dB), outside the reach of most current (and certainly vintage) amplifier designs. So for amps having lower amounts of feedback (or none at all) excess capacitance is used.

Because that current rating is actually a rating of how much current will flow if the power supply were to be shorted out (IOW nothing to do with the actual full power of the amp) you wind up with some advertised claims of 'current' which are pretty outrageous. The article I linked from a prior post explains in simple math how outrageous those claims would be if they were meant to be the actual current the amplifier is able to make into a speaker load!

Would love to see your system, or know what’s in it. Do you use power management in anyway?

I don’t (but have a number of customers that do). My preamp employs heavy power supply regulation, which helps out immensely, and my amps employ over 35dB of feedback and are able to reject power supply noise and also employs regulated power supplies. Both also have built-in DC blockers. Equipment that lacks that sort of feedback and/or regulation needs all the help it can get.

I did rewire the audio room AC wiring, complete with Hubble AC outlets.

I’m a power supply guy and it occurred at a show in a discussion with Nelson, who is also a power supply guy.  I, too have read about that number in reviews...

OK. What is far more likely is that the 48 Amp value is actually how much current is present when the power supply of the amp is shorted. Its available to the output section in the form of charged capacitance. This is used to help reduce IMD in the output section and is not something that the output section can pass to the loudspeaker (if you see what I did there 😁).

I've read that link several times in the past.  BTW, I like your amps!

The quote came from Nelson Pass.

@piaudiol 

I've seen advertising, but not the actual quote (which IME is something very different!). Do you have a link?

But tell me, can we cheat and just add a resistor in the line to a lower impedance speaker and get the same enhancement of performance from the amp?

Yes, but the resistor will work against you than for you. It will absorb power too- for example if a 4 Ohm resistor in series with a 4 Ohm speaker, the resistor will absorb about 1/2 the power! Its not practical, and the speaker will see a vastly reduced damping factor.

A Class A PASS XS300 monoblock will dump 48A on demand.  You need two of these.  See where this is going?  

@piaudiol 

This seems really unlikely!! Giving the amp the benefit of the doubt, and assuming it can double power into 2 Ohms, it would be making 1200 watts. If it can do that the current would be about 24 Amps. To do 48 Amps, the amp can would drive 1 Ohm with 2400 Watts (that would be 48 Amps of current) and I just don't think so. The math is against it.

You might want to read this:

http://www.atma-sphere.com/en/resources-common-power-amplifier-myths.html

Whomever you got your information from was misinformed, IMO.

@atmasphere do you have experience with your amps benefiting from using the two example of power conditioning units that you mentioned?

Yes.

@atmasphere great discussion of these two power conditioners.  I wonder 2 things: 

1.  How much load do they add?  To supply a 400W amp does the load (and heat in the room) go up to 800 watts?

To supply a 400W amp the total draw is likely about 475-500 Watts.

2.  Are these expensive high end units able to totally eliminate transformer hum?

Maybe! If the transformer is noisy because there is a 5th harmonic, then yes. If the transformer is noisy because of DC on the AC line, then very likely yes also (although a $50 DC blocker can sort that out). If the transformer is noisy out of its load and/or design, then no.

I guess, what I wonder, is if some “power conditioning” devices still may add value.

If passive devices, it can, and will be marginal.

I’m going to research more into the 240 V option that makes sense. Does anybody else know anything about this?

Yes. If you are having problems with AC line noise, this will do nothing since the noise is coming from outside the house. Your house is powered by 240V which is split into two halves; that's what electricians are talking about when they talk about 'the other side of the line'. You can see this by simply looking at your breaker box- the left and right columns of breakers are the two sides of the line. There is no transformer involved to cause the two sides to be 117V  (or 120V or whatever).

Power cords obey Ohm’s Law. Voltage drops across them can cause a very measurable loss of power in an amplifier. In that manner it can affect distortion and output impedance too.

The voltage drop is easy to measure with a regular digital voltmeter. So this isn’t anything mysterious.

A good power conditioner is helpful too. A glorified power strip that gets called a ’power conditioner’ is not. The latter forces all the equipment to obtain its power through the same power cord, FWIW.

A proper power conditioner will not limit current, it will be able to guarantee the AC sine wave distortion (you’ll see that in its specs) and should be able to regulate the AC line voltage. One of the more pesky AC line aberrations is the 5th harmonic, which can cause power transformers to become noisy, power rectifiers to become noisy and can affect synchronous motors found in turntables and tape machines.

There are very few power conditioners offered to high end audio that can do everything I’ve mentioned here.

That means that most people on this thread, in particular those that think power conditioners don’t make a difference, simply haven’t heard what a proper conditioner can actually do. Its not as if they are wrong; most of what they have heard simply doesn't work!

That is why there is controversy on this topic.

I know of only two power conditioners that seem to work. One is made by PSAudio. The other was made by a company called Elgar, who got out of the power conditioning market a long time ago, so if you find one of their conditioners (they show up on ebay) its likely it will have to be refurbished.

A proper power conditioner has to have active components- if passive (for example a choke or transformer is all that’s involved) it won’t work. To give you an idea of why, let’s take the Elgar as an example. It has a low distortion 60Hz oscillator that is synchronized to the incoming AC power. The AC power goes through an isolation transformer that also has windings to run the conditioner’s internal power supplies. Feedback is taken from the output and compared to the low distortion oscillator; this correction voltage is applied to the isolation transformer as correction (through a power amplifier built in); in addition it also is used to buck the output voltage so that voltage is thus regulated without current limiting.

That’s a bit of sophistication! If you don’t have that in your power conditioner, it can’t filter out the 5th harmonic, it won’t be able to correct line voltage, it won’t be able to provide a clean AC waveform to your stereo. Put another way, +90% of all ’high end audio’ ’conditioners’ are so much junk.

If y’all want to argue about this topic, at least have the facts available!