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Old 30th October 2015, 10:23 AM   #1
nareshn is offline nareshn  India
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Default Measuring Amp output V and I

Used a true rms meter at AC setting to measure o/p voltage of a amp ....the reading is only in mV when the loudspkr is working?
Is it because the meter is limited in freq ?

Also plan to use a true rms clamp meter to measure the output current into the loudspkr? not sure if this will work either ?

Any pointers to existing threads appreciated.
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Old 30th October 2015, 10:41 AM   #2
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Play a 1kHZ tone, measure the AC voltage across the loudspeaker. P = V / I.
You know V. You know R. You can work out I as I = V / R. You now know P.
P is in Watts
V is in Volts
I is in Amps.
R is in Ohms.
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Old 30th October 2015, 11:42 AM   #3
DF96 is offline DF96  England
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For most speakers in most rooms playing music at 'normal' volume levels (i.e. much lower than 'live' levels) the voltage will be small.
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Old 30th October 2015, 12:05 PM   #4
AndrewT is offline AndrewT  Scotland
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Originally Posted by DF96 View Post
For most speakers in most rooms playing music at 'normal' volume levels (i.e. much lower than 'live' levels) the voltage will be small.
Indeed, average levels around 100mVac are quite common.

You need to send a known, measured, test signal into the input and measure the output.
Pano has a test to do exactly that and gives the file to record to a CDR to provide the test signal.
And a DVD player can read and send the correct test signal.
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Old 30th October 2015, 12:20 PM   #5
AJT is offline AJT  Philippines
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Quote:
Originally Posted by nareshn View Post
Used a true rms meter at AC setting to measure o/p voltage of a amp ....the reading is only in mV when the loudspkr is working?
Is it because the meter is limited in freq ?

Also plan to use a true rms clamp meter to measure the output current into the loudspkr? not sure if this will work either ?

Any pointers to existing threads appreciated.
with speakers, power is simply not the same as with a dummy load resistor...
a couple of months back we confirmed a Crown clone amp of 1kw (FTC) output into an 8ohm dummy load....

using a kill-a-watt device, with music playing into our speakers at chest pounding and ear splitting volumes, power draw from the mains was l little over 200 watts...
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Old 30th October 2015, 01:11 PM   #6
Pan is offline Pan  Sweden
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Due to the reactive nature of a loudspeaker you can not measure Vrms and Irms only to arrive at consumed power, you need to include phase angle as well.

Also, naturally, a 1kW amp playing nice music will have average power much less than 1kW unless you clip the amp like crazy. Music is normally (hopefully) a dynamic signal. Dynamic range may be 10-20dB (average to peak) for most music.
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Old 30th October 2015, 03:48 PM   #7
nareshn is offline nareshn  India
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Originally Posted by AndrewT View Post
Indeed, average levels around 100mVac are quite common.

You need to send a known, measured, test signal into the input and measure the output.
Pano has a test to do exactly that and gives the file to record to a CDR to provide the test signal.
And a DVD player can read and send the correct test signal.
A Test. How much Voltage (power) do your speakers need?

Does the spkr need to connected when the test tone runs.
The spkr i have are 4Ohms .
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Old 30th October 2015, 04:08 PM   #8
AndrewT is offline AndrewT  Scotland
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You need to set the vol pot with the speakers connected. After that you don't need the speakers.

But you are only trying to measure the output with a test tone input. You don't need speakers for that.

You need an amplifier that is 4ohms capable.
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Old 30th October 2015, 05:41 PM   #9
gdan is offline gdan  Greece
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Maybe you are interested on this:
Voltage and Current Peak Detector

regards
George
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Old 1st November 2015, 11:22 AM   #10
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If you have a look at this thread on Speakerplans, the measurement method used should do what you are looking for as well as provide you with additional information: Power Factors for 'Speakers - Speakerplans.com Forums - Page 1 Mik
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