2. amps-preamps
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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
draw.
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.
noslepums

Showing 3 responses by magfan

magfan
1,583 posts
 
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.
magfan
1,583 posts
 
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.
magfan
1,583 posts
 
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.
OR
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.
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