# Voltage/Amp Requirements for Audio Amplifiers



## Talley (Dec 8, 2010)

I'm the type of guy that tinkers and one of things I've done is purchased a Fluke 289 Industrial Logging capable multimeter with an i400AC clamp accessory. For those who know me and know that I've done pretty radical work on my power feeders to my AV equipment know that it may of been a bit overkill. But... is it really?

My new meter will arrive within the next day or two and one of the things I want to test will be voltage drop, peak ampacity, sustained ampacity, etc for my feeders connected to my amplifier and my subwoofer. We all know that most subwoofers with built in amplifiers are rated RMS/Peak. I'm curious to see what effect these amps have on the AC line supplying the equipment. With the logging meter I'll know to within 0.00025 seconds what requirements are what. I'll soon be able to post graph data of the current draw/voltage drop and more.

Even better? I have 8 dedicated circuits in my outlet box... I have one feeder with a large #4 wiring. 3 are #8 and 3 are #10 and one circuit that is #14.

So.... I'll be able to move the amp from the #4 circuit... to the #8, #10 and even try it out on the #14 15amp circuit as well. My distance from the panel is short... 63 feet to be exact. I'll be able to really load the sub down with some heavy organ music and/or fight scenes that are intents like the Hulk movie and graph the voltage/current on the AC line and to find out what gauge wire is needed for these situations. Find out what is overkill and what is not enough.

Now... what will this test prove?... nothing except for the hard data on the AC lines. Will that be audible? This is the debate. What is the peak wattage on my amplifier during reference playback?... lets find out.


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## Tonto (Jun 30, 2007)

The last time I checked my system, with 2 Klipsch KSF 8.5's, the SC-1 center & my SVS PB-13U. It pulled up to 1700 watts during some intense scenes. Not on a dedicated circuit. My APC S-15 shows how many watts are being used in real time. Not the same stuff you'll be measuring, but the standard wiring in my house doesn't seem to have a problem yet. Looking forward to your results.

I'll have to check what kind of breaker I have on the dedicated circuit for my HT. Is there a recommended amp rating for HT equipment (15 vs 20 amps)? I know my freezer needed a 20 amp receptacle (had to change it to pass inspection), but I don't know what this means at the box. Sorry for my ignorance bout electricity.


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## Talley (Dec 8, 2010)

Tonto said:


> The last time I checked my system, with 2 Klipsch KSF 8.5's, the SC-1 center & my SVS PB-13U. It pulled up to 1700 watts during some intense scenes. Not on a dedicated circuit. My APC S-15 shows how many watts are being used in real time. Not the same stuff you'll be measuring, but the standard wiring in my house doesn't seem to have a problem yet. Looking forward to your results.
> 
> I'll have to check what kind of breaker I have on the dedicated circuit for my HT. Is there a recommended amp rating for HT equipment (15 vs 20 amps)? I know my freezer needed a 20 amp receptacle (had to change it to pass inspection), but I don't know what this means at the box. Sorry for my ignorance bout electricity.


Just depends on the equipment. Most AVR only require around 700 watts. A 15a you can load to 1440w per NEC and 20A to 1800w. If you have dedicated separates then it's a tad different of as story or a high power amp for a sub type thing. Example is the Emotiva XPR type amplifiers have very potent 3300w power supplies so the requirement for a dedicated 20 amp circuit is key even having 240V.


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## Talley (Dec 8, 2010)

Well my Fluke 289 has arrived. So awesome :wave: what didn't arrive is the clamp on amp meter so I can make power measurements. It shows up tomorrow.

Here is a sample though taken at a random outlet in my house (12g wire) was stable at 122 volts. Plugged in a vacuum and turned it on and back off for a second then turned it on for and ran it for several seconds. The vacuum is rated 12 amps 120v. As you can see the voltage drop on initial startup was 9.16 volts on a 12 amp motor load. Then running was right at 118 volts or 4 volts from stable = 3.2% drop which is actually unacceptable to the NEC (3%) BUT this is a momentary load so it's OK. Still... a 9.1V drop at startup.... thats an initial hit of 7.4% eeek. This is the affect at the receptacle the vacuum was plugged into and what it has. The other small dip at 41 seconds is me turning the rollers on which again did a small drop. The resolution on this was around 1/4 second or so... maybe finer than that. I'll have to see if it'll log min/max peak which will really dial in some numbers as it has a 250 micro-second resolution.

I wonder if this was your power amp from quiet to dynamic explosions if this amount of swing would be audible or not. Again this was pushing probably 1400-1500 watts and it's a motor load... you can see that the motor was still going when I turned it on the second time so the voltage drop wasn't so much of a hit... around 115.x volts.

Either way... a quick photo to drool over.


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## Talley (Dec 8, 2010)

HA I just checked the math. I'd estimate this outlet is around 85 feet from the panel. If you figure in the 120v line and 12 amp load on 12g wire the math works out to be *3.2%* which is exactly where the running vacuum cleaner was operating at... 118V!!!

Now... if I had #10awg wire the math drops to 1.9%.... if it was #8 awg wire would drop to 1.3% and if it was #4awg the math drops to *0.5%*... which is exactly what my amp is wired up to. 

what is .5% voltage drop work out to at the 122v? a drop of .6 volts.... or 121.4 volts. Recap:

122V line
14awg - 115.9V (a staggering 5%)
12awg - 118V
10awg - 119.6V
8awg - 120.4V
4awg - 121.4V

I think I prefer the #4 feeder for my amp  More testing coming soon.... with reference level amplfication test graphs :hsd:


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