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Old 26th September 2004, 01:59 PM   #1
Zodiac is offline Zodiac  United States
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Default Measuring amplifier gain

Is it possible to measure amplifier gain using just a digital multimeter? I was thinking to input a constant sine wave, like 100hz, and measure the voltage using the multimeter on ac mode, then measure the output of the amp.

If I can do this, do I need to load the outputs of the amplifier whilst measuring the gain or not?

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Old 26th September 2004, 03:30 PM   #2
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You can for example take 100 mV in and then you should have 2-3 volt out. You don't have to have a load at those levels and frequencies
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Old 26th September 2004, 09:14 PM   #3
Zodiac is offline Zodiac  United States
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Cheers, I will give it a go and post the results here.

I am doing it so I can equalise gain in an active speaker with different amps for the bass and mid / tweeter
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Old 26th September 2004, 09:36 PM   #4
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A digital multimeter will work, but not well for higher frequencies.
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Old 27th September 2004, 07:18 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi, Do you know how to build a switched variable attenuator? All you need is a bank of double pole switches and some accurate resistors.
Can anyone out there post a circuit layout?
Provide attenuation of -20db,-10db,-5db etc. down to the level you require. Insert this on the input to your amplifier. Set up the switches to give the output level exactly as the input level from an oscillator or even a test disc in a cd player. Since the AC reading multimeter is now comparing the same voltage at input and output it ignores error in frequency response of the multimeter and can be used effectively over a very wide frequency range. I have taken readings upto 150kHz to check the frequency response of a range of power amps. I cannot work @ very low frequency because my multimeter samples the waveform and @ less than 12Hz it becomes very difficult to take sensible readings.
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Old 28th September 2004, 09:35 PM   #6
Zodiac is offline Zodiac  United States
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Default Done. I think (!)

OK, so I measured the input and output voltage, the voltage gain was 20.3, which is near enough 26db

I want to take 6db off this, so I figured an attenuator circuit 10k in series with signal and 10k to ground after this would do the job.

This will then equalise my Nakamichi PA7 (26db of gain) with my Pass Labs Aleph 3's (20db of gain) .... I think!
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