# Re: Electric current for same output: 110V vs 240V

Lawrence Logic <mr-NotThisBit-logic@xxxxxxxxx> wrote:

Thanks for your response, although you may need to recalibrate your
calculator. If P = I*V, then I = P/V (dividing both sides of the
equation by V to leave I on its own as the value that we're trying to
determine). If P = 175 and V = 240, then I would be about 0.73
(175/240). For 110V, the current drawn would be roughly 1.6 amps
(175/110).

I understand that the power consumed doesn't necessarily bear any
relationship to the power shoved out through the front. It does
raise an interesting point though. Is there any rating of effective
power for the output of an amplifier?

A good example of what I'm talking about was an occasion when my old
Peavey Classic 30 was turned up to about 3 (out of 12) and its output
via its single 12" speaker totally swamped a Yamaha G100 transistor
amplifier turned up full and delivered via 4x12" speakers. The
numbers meant nothing because a valve amp will generally be much
louder than its solid state equivalent. Even the difference between A
class, B class and A/B class valve amps is pretty much immeasurable.

It would be nice to have some sort of absolute rating that really
gave an indication of how loud an amplifier would actually be.

1. You've got to consider speaker efficiency as well. There's a pretty
wide variation in speaker sensitivity ratings and this quantity gets
folded in when determining perceived loudness.

2. Amps are often rated power-wise in terms of the highest output power
produced without exceeding a given level of total harmonic distortion
(THD). The thing is that, within certain limits, we perceive distortion
from tubes as pleasant and that from transistors as unpleasant. So a
tube amp can run well over this THD limit and still sound good, whereas
generally a SS won't. That's why, given the same speakers, a tube amp
comes across as "louder". In audio applications rather than guitar and
bass amps, that same tube amp run into that distorted regime would be
unacceptable because there's too much distortion and you don't get a
faithful replication of the input signal.

.

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