[Cjattwood]

Great post ferbose with lot's of thorough and detailed information. Thanks for the info!

 

[audiorapture]

Ferbose: great info, thanks for the time and effort. I can see opinions being changed by this............

 

[JiggaD369]

So is it ok if I use a UPS System for home theater instead of a so-expensive audiophile power conditioner?

 

[Ferbose]

Quote:

Originally Posted by JiggaD369 So is it ok if I use a UPS System for home theater instead of a so-expensive audiophile power conditioner?

As far as I know, UPS systems may have a couple of problems for audio applications:
1. Fan noise
2. Many UPS don't output sine-wave AC, but some distorted waveform. Most UPS systems are designed for computers, and I assume the switching power supplies in computers don't really care about AC waveforms.
3. Instaneous current capability: a 200W SS amplifier can draw up to 30A of instaneous current during musical peaks

But then again, an UPS might work well in your system, which is hard to predict.

 

[CookieFactory]

Quote:

Originally Posted by Ferbose 3. Instaneous current capability: a 200W SS amplifier can draw up to 30A of instaneous current during musical peaks

lol well there goes the Universe!

 

[JiggaD369]

Damnit. lol. What about those Monster home theater power conditioners?

 

[Ferbose]

I heard that Monster power conditioners aren't bad, unlike most of their overpriced cables. I never used one myself.

On the other hand, Furman is the MAJOR brand in pro-audio power conditioners. I figured, if musicians and studios trust Furman's products, why should not I? So far I like what I am getting out of my Furman conditioner.

 

[Publius]

To a large degree, hospital cables don't need shielding because it's not supposed to be the job of the cable to improve the signal. You either use a power conditioner or you use a power supply that does a proper job of providing a good DC output. Have you seen hospital-grade power supplies? They are large. And quite often linear too.

IOW, at least from a semi-objective point of view, it's entirely possible that a piece of equipment does need a shielded cable for optimum performance. But that usually implies that the power supply is inferior for the specifications that are being expected out of it.

 

[soultek]

Hey all, here's my first post.

Ferbose, that's good research, unfortunately I feel like audiophiles are barking up the wrong tree with high end AC power cords. (there's SO many other things to spend money on that make more of a difference)

A few points:

POWER FACTOR largely has to do with the efficiency of a power supply. From a user perspective, it should be transparent. If the power supply is designed properly, then any large quick transients will draw current from the bulk capacitors. Although a non unity power factor implies a voltage/current phase lag, this is never heard since the bulk caps should damp any transient current draw that is faster than 60Hz.

POWER FACTOR CORRECTION is not necessary for good audio performance, it mainly improves the efficiency of the AC power network from the power plant to the power supply in your piece of equipment.

WIRE GAUGE is quite a silly spec for an AC cable. The resistance of the wire will not affect power factor, the power factor only changes with a reactive load. The important spec for wire gauge and jacketing is all safety related. As noted, the contact resistance in a typical AC plug probably has more resistance.

SHIELDING is quite useless for an AC input cable. Assuming the device in question is designed good, it will have RF filtering at the AC input of the power supply. Also the box will be metal and earth grounded no doubt? between those two measures, it's quite easy to kill any RF problem. The only implication is that the electrical field of the AC power cable can couple into the circuitry. Not if the box is electrically shielded, which most are.

WIRE MATERIAL is also kinda silly. All this would do is improve the DCR and maybe improve stray capacitance, but this would have no effect on the signals in the box. The stranding of the wire doesn't matter much unless you're worrying about flexture.

POWER CONDITIONERS do work well if well designed. I've heard some good things about the Monster products. If you have a relatively clean AC supply, and a well designed device, then you will probably not see any difference whatsoever. Spend your money on more audio gear.



I realize this is a touchy subjects, there's a lot of people that want to justify their exorbitant purchases and there's still more who want to make a living selling snake oil. I'm just trying to add my two cents from an audio designer's perspective so that people are not decieved out of their money.

Also I've been wrong on many things before, the bottom line is people LISTEN! If you can hear a difference in a blind listening test, then something's happening!

 

[Ferbose]

Clearly I am not an EE, so the power factor issue may be somewhat beyond my understanding. Do other appliances in the house with highly reactive loads increase the outlet's impedance?

If I understand correctly, linear power supplies only draws current during a small fraction of a 60Hz cycle. Therefore, the maximal instaneous current could be 2-5 times larger than current computed from continuous power P=IV. That means a 200W SS amp at its peak output will draw 800W of continuous power (assuming two channels and 50% efficiency). For a 120 V outlet this would mean 6.7A of RMS current. Instaneous current could be as large as 30A.

If the impedance of the outlet is 0.2 ohms, 30A would cause a voltage drop of 6V. A cheap stock power cord could have 0.1-0.2 ohm impedance due to thin wires and suboptimal contact, which could add another 3-6V of voltage drop. If I am not mistaken, other appliances in the house could cause the outlet impedance to go even higher, causing even more voltage drop. The combined voltage drop could now amount to more than 10%. Though I am not an expert on power supply, it seems to me that amplifier performance (output power and distortion) could be compromised if AC voltage drops by something like 15V. Of course the actual problems caused by high AC impedance could be more complex than the simple analysis I outlined.

Clearly, using a thick power cord with nice plugs is only the first and less significant step toward tackling AC-related problems. Some also try to replace the wall outlet itself. But it seems to me that a suitable power conditioner is the answer to most AC issues.

 

[Ferbose]

A good link that helped me roughly understand power factor:
http://www.ibiblio.org/obp/electricC.../AC/AC_11.html

 

[soultek]

Wierd things can happen with wall outlets and home AC power systems in general. I depends on how the system is wired.

I see what the concern is here.

First of all is the issue of amp power ratings. Typically amplifiers are rated by running a sine wave through the amp to a resistive load and then noting at what power output 1% or 10% THD is measured. Important to note that this is done with a SINE wave. Sine waves are very different from music: they are continuous, have no harmonics, and have a different crest factor. Crest factor is important here. Crest factor is basically the signal difference between peak and RMS. For sine waves this is ALWAYS 3dB. For music it varies. For pop stuff, it could be 6dB, for more dynamic stuff it could be as high as 20dB.

Now,

The point of a well designed power supply should be to account for everything: low and high line voltage (usually designed to account for +/-10%), rated power out of the amplifier, temperature, etc.

So,

If the amplifier is designed well, it should draw all it's instantaneous peaks from the power supply, and NOT from the line.

Typically, with an unregulated power supply in an amplifier, the droopage of the voltage rails in the box will be related to the power transformer more than anything. When magnetic flux of the core starts to saturate, the voltage will droop. This is why really nice amps sometimes have HUGE toroids in them.

Bottom line is that for a TYPICAL LINEAR AMP a 200W SS amp will NEVER be dumping 200W continuous into speakers. Think about it in the terms described above. If the amp is rated at 200W, that means that it can pass a sine wave to a specified load at 200W. For the sake of arguement, lets say the amp is mono, is a voltage amplifier, and the power supply is linear, and that the load is 4ohms. So that means that the load is seeing 28.3Vrms. If the amp trys to deliver more power to the load, it will square off the wave and sound terrible. This is the ceiling on the performance. Therefore, with music with a crest factor of 20dB, and running music signal in with no sqared off peaks, the RMS level of music would be around 2.83Vrms at the load with peaks as high as 28.3V. This translates to about 2W or average music signal. Now this is very controversial in the industry, but it's a much better way to understand this stuff than with just sine waves.

This explaination doesn't cover transients really. So what's the worst transient really? a 20Hz pulse at full peak (28.3V). The power supply should store enough juice to be able to deliver this to the amplifier. What would happen is the resivoir capacitors in the power supply would drain to provide the current necessary to drive the load. Then it would start to charge back up after the transient (MUCH slower than the speed at which the transient hit). Now you may ask, what if it's hit repeatedly with 20Hz transient peaks. Well, the answer is that that is very very very unlikely in music, and any well designed amp should account for all these things.

Now, all this discussion focuses on standard, voltage amplified, linear supply, solid state amps. There's a lot of wierd stuff out there that might act differently.

hope this helps..

You could always take a reasonably equipment multimeter and measure some of this stuff for yourself.

 

[Ferbose]

After trying some genuine, 16 AWG, low-leakage, hospital grade power cord from Volex (Belden), I am not impressed with its sonic result. This is already the best "true" hospital grade power cord I managed to find. I still prefer black, pre-molded, shielded power cords. Nor did a 10 AWG, silver-plated copper, unshielded, fat-ass cord with big hospital grade plugs impress me.

Not sure why power cord shielding works in my system because all my audio interconnects are far away from power cords. Now my favorite is Volex's 14 AWG, shielded 3 ft cord. $14 for very-low-impedance, shielded cord for a world-leading brand--I can live with that. A logical upgrade from those sotck, 18 AWG, garden-variety brand IEC power cords.

 

[John Massaria]

The best thing I can personally suggest is to invest in a dedicated 15A-20A single pole circuit breaker for your digital equipment and AND MAYBE another 15-20A for your amplifier/preamp/headamp. Using 12 gauge or better yet 10 gauge romex type wire. Another suggestion while your electrician is there- ask him to tighten all grounds connected to your box. To quote an article I read from PS Audio (not a fan or not of PS Audio mind you)- "A dedicated AC line is simply a separate AC wire going back to your home’s circuit breaker box. Instead of the standard AC feed with multiple AC outlets available for many pieces of equipment, a dedicated line is a “home run” single-use wire from the equipment it powers all the way back to the circuit breaker box where the AC power comes into our homes.... For less than the cost of a budget power amplifier-a mere $373.45—the electrician ran two new 20A lines to the listening room, one with the hot on one side of neutral, the other on the other. Each had its own circuit breaker and each fed two hospital-grade wall sockets. (These orange receptacles grasp the prongs of AC plugs with a clasp akin to the Vulcan death grip.)" Hope this helps- when you sell your home its a feature some buyers may love- but in the time in between you will have musical bliss blowing away any cable purchase or maximizing equipment purchases you can make. You could also do a isolated ground- and a metal box thats also grounded.

 

[Speedskater]

Isolated Ground receptacles are for circuits that are wired with metal conduit (ridge or flexible). Romex® cable does the isolating all by itself.

Also, post #1 in this old thread is well worth reading.