Amplifier Watt Meter

[Philippe]

Where in the amplifier output circuit do you attach a watt meter & lastly, what's a good type of (inexpensive) analog meter to use? Something with a needle would be fine, no flashing lights or LEDs.

[brett]

Hi
W=A*V
A=V/R
for a speaker, R might be 8 ohms (nominally - it will vary with frequency and voltage)

For R=8, 8V = 1 amp = 8W.  16V = 2 amps = 32W.  So you can see that W varies non-lineearly with volts and linearly with current.
So you could put a ammeter in-line with the speaker.  Better still, put one in-line with a 1 k ohm resistor.  Then 8 V (8W) = 8/1000 = 8mA.  Low current and nice and proportional  .
cheers 

[gmoon]

If you're lacking a 'scope, signal generator and such, here's one way to get a "ballpark" power measurement:

-- connect a voltmeter across the speaker
-- plug in and play, write down the voltage
-- square that, then divide by the load impedance

I.E., 12V reading, 8 ohm load : (12 * 12) / 8 == 18 watts

Not highly accurate (differs with input frequency, etc.), but useful...