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Amps, Cables and Current: A Question

Hi folks. I have a few questions I'm wondering if you can help me with....

1. I've seen some amps, such as the Odyssey Monos, that list peak current capabilities around 65 amps. How is it possible to deliver that kind of current when the unit is connected to a wall outlet that is fed from a 15amp circuit?

2. I've been having a email dialogue with the folks at Audience. I'm still confused by their response. According to them, "the Audience power cords need to be thicker because they carry so much current. A power cable the same diameter as the Au24 speaker wire would be a fire hazard" because it would not be able to carry all the current coming from the wall. They continue by pointing out that the speaker wire can be thin because it carries much lower current than the powercord.

If you understand what I've said here I think you can see my confusion. If an amp like the Odyssey is putting out 65 amps of current then that far exceeds what is coming out of the wall and therefore my thin little Au24 should be melting or causing a fire or something, no?

I'm no electrical engineer, obviously. I have to be missing something. Can anyone help?
dodgealum
4 responses Add your response
ampnut
7 posts
 
On yr second question ...

The total POWER ( not current) consumed from the Wall outlet is the Max POWER ( not current) delivered to a speaker load, on a continious basis.

The AC Power charges up Capacitors in the amp that can dump Very High Instantanous ( Peak ) power into the speaker load, but on a continious basis, the power to the Speaker canot exceed the Power drawn from the wall.

Most Audio power amps ( Excluding the recent Class D, T and other switching amps ) have an over all efficiency of about 50% or Less.

That is why the Power Cord actually carries more Power ( Not necessarily more current ) than the speaker wires.

POWER = Voltage x Current

Hence 200 Watts drawn from the mains @ 120 VAC implies a current of 1.67 Amperes.

Power is also = Current x Current x Resistance

Hence a 100 Watt, 8 Ohm Speaker load draws ( Per channel ) a current of 3.5 amperes.
gs5556
769 posts
 
That 65-amp currennt delivery is misleading. You wall outlets are supposed to deliver 20-amps. If you short it out with a piece of copper, you could get as much as 10,000 amps short-circuit current. The 65-amp "peak current" is the same thing - what it's capable of producing under short-circuit conditions, or the reservoir capacity of the power supply.

The amplifier current is determined solely by the speaker load. (See jeffreybehr's post). Current can only flow through a resistive load, and the value of the resistance determines the current. But if you short the speaker wires together, you will probably get that 65-amp current - blowing all sorts of transistors and electrical components, as well as melting the speaker wire.

Just goes to show that some manufacturers, just like magicians, try to divert your attention from sonic performance by waving around big electrical performance numbers.
dodgealum OP
976 posts
 
Thanks, Jeff. Point #1 is as I suspected. However, Point #2 I don't get. Can you put it in somewhat more layman's terms? And in addition, can you address why the Audience speaker cables do not present a problem handling the kind of "peak" output current some amps deliver even for only a fraction of a second? Thanks.
jeffreybehr's avatar
jeffreybehr
805 posts
 
1. The powersupply capacitors discharge. It's called 'peak' because that high current draw can occur for only fractions of a second before the caps are 'empty'.
2. Current delivery is related directly to Voltage and inversely to impedance driven. 120VAC has little to do with low-Voltage music signal delivered to speakers. For instance, 100 Watts into 8 Ohms is only 28 Volts-AC at about 3.6 Amps.

You're really making fruit salad here, Dodge. Don't try to equate these 2 substantially different situations.
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