Amplifier current draw/wattage

Hello All,
Trying to figure my system's total power requirement.
I'll have 12 devices plugged into the wall, or some kind
of power supply. By reading fuse sizes and/or power
consumption, I come up with about 24.75 amps (120-VAC).
This is only steady-state operation and I don't think
includes startup surges. The power amps take most of this
I feel fairly comfortable with the accuracy of this figure.
Here's my point of uncertainty: I do not know if the
amplifiers draw more current as I increase the volume.
I have 4 amps (powering 4-way speakers):
Bryston 3B-ST..............5-A fuse
Linn 5105 - 2 of these....."6.3-A MAX"
NAD 2600a..................5-A fuse
So at peak current draw the 4 amplifiers would supposedly
draw about 22.6 amps.
Can anyone tell me what class each of these amplifiers
belongs to, I know only that none are class A.
I can certainly supply more info if anyone asks.
Does my reasoning seem sound ?
The whole result is that it appears I need to add
a new 30-A circuit from my breaker panel, probably
with 8-ga wire. This will be a fair amount of work.
No no no.
The total peak draw would only occur at max output.
An amp like the Bryston 3B-ST will only be drawing a fraction of that power.
What you want to do is find the idle wattage. Then the maximum wattage actually used.
The fuses are not an indicator of amperage used.
I would say your three amps if used to play music at Rock Concert levels.. might start needing a lot of power.
As they are normally used. 15 amp circuit would be fine.

So if you plan on having endless 120dB concerts.. you do not need 30amps service.
A 20 amp would be fine for all your stuff.
Elizabeth is correct. The fuses are there for protection in case something goes wrong with the amp and it suddenly draws excessive current. you will be ok with a standard 15 or 20 amp circuit
You can get a watt meter at Home Depot for about $20 that will give you a digital readout. It also reports current drawn, voltage, freq. and other cool stuff. I use mine to very accurately read idle watts being used on various equipment. If you plug all your stuff into a nice power strip, then into the meter then the wall you will get your answer.
Bryston 3B SST: 668W @ 150W (8 ohm), 1096W @ 250W (4 ohm)

Linn 5105: 25-850W. 4700 ohm input impedance might be interesting for your setup.

Divide by 115 to get amps.

Didn't find particular specs on NAD.
Spend the 20$ or so on a 'Kill-A-Watt' meter. This will allow you to MEASURE what you are curious about.
If you are plugged into a 20 amp circuit, you must derate by 20% for a continuous load....something like 3 hours is the time limit.

The meter will also allow you to check out 'power factor' which is an indicator of how reactive the load is. Watch your power line voltage sag as the load increases. Fun stuff.
At normal listening levels, I've never seen either my 2-channel or HT systems draw anything over 6A.
Does the "Kill-A-Watt device allow measurement of power amp wattage used to drive a speaker load or just current draw fom AC outlet?
The 'Kill-a-Watt' plugs into the wall and the device under test plugs into IT. Speakers are different impedance and different reactance at all freuqencies so a single number representing the speaker won't work.

Everything in the meter is calibrated / set, for 60hz. A broadband signal? I'd recommend starting with a scope and a true-rms meter if you want to measure speakers. Add a test tone CD, perhaps.
Hi Magfan,
I don`t want to measure speakers, but want to know the power output of the amplifier at different volumes. IOW how much power is used at say SPL of 70db vs 85db(how hard is the amp working) measured in watts.
01-17-12: Charles1dad
I don`t want to measure speakers, but want to know the power output of the amplifier at different volumes. IOW how much power is used at say SPL of 70db vs 85db(how hard is the amp working) measured in watts.
Charles, that can be calculated (to a reasonable approximation). Caveats are that the calculation assumes that speaker efficiency (or, alternatively, voltage sensitivity and impedance) is known accurately, and that the calculation neglects the contribution of room reflections to SPL.

Your Total Eclipse II's are spec'd at 94 db/1 watt/1 meter. For a box type speaker (as opposed to a planar) subtract 6 db for each doubling of distance. Add 3 db to approximately reflect the presence of two speakers.

So at a listening distance of 4 meters (about 13 feet), 1 watt per channel would result in an SPL of 94+3-6-6 = 85 db.

That figure can be adjusted to reflect different power levels based on the db relationship of the ratio of two powers, which is 10logarithm(P1/P2). From that it can be calculated that a 15 db reduction in SPL corresponds to reducing the power level by a factor of 31.6. So a 70 db SPL at 4 meters would correspond to (1 watt/31.6) = 0.032 watts.

The 8 watt maximum power rating of your Franks would correspond to an SPL at 4 meters of 85 + 10log(8/1) = 94 db.

For other listening distances, adjust up or down based on 20 times the logarithm of the distance ratio. For instance, the SPL at 3 meters would be higher than the SPL at 4 meters by 20log(4/3) = 2.5 db.

Best regards,
-- Al
Another, more obtuse path to the same data would use an SPL meter, test tone disk and a good DVM or scope....scope preff'd. The voltage at the speaker is related to *power* to the speaker.
You could also measure watts used...of the amp, and calculate backwards using probable efficiency of amp. Hi/Lo estimates will yield a range of powers.

Al's method relys on knowing the sensitivty of the speaker. Not always reliable or even measured the same way.

BTW, Charles, amps need a load to generate power. So, in that sense they are entwined. Don't run any tube gear without a load or you'll get another lesson in electronics....and the bill to prove it.
Hi Everyone,
For me, this thread has been quite helpful, thank you !
Elizabeth, I believe I could have described my problem
with better wording, but I do understand and agree with
your explanation.
Ngjockey, you raise a good point about impedance matching;
another variable I should examine closer.
Koestner, I don't know why I didn't think of getting
a wattmeter myself.
So, hopefully I'll be fine with a normal 20-A supply,
and listening to the music at semi-sane levels.
Hello AL,
Thanks for your response. Al I already knew the calculation and realized that at my listening distance= 9feet and usual sound levels=70-85db(depends on recording) I`m only using small fractions of a watt! I was just curious to know if the inexpensive device could measure and confirm with an actual meter readout.
Best Regards,