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Old 28th June 2010, 09:12 AM   #1
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Exclamation Tone generator output Voltage for amplifier measurement?

Hello,i'm viewing this forum for whole years,really great work!

Since i want to measure an amplifier and i don't have a function generator i'm using my sound card to do that.

The problem is the following:

I have a lot of software tone generators set on 3db but i'm getting a different voltage from them.

For example if i set the NCH Tone Generator to 3db and the sound card to 100% i'm getting on the sound card's output about 445mV RMS,but if i use another tone generator i'm getting another number lower or higher.

The question is,how much Volts RMS am i supposed to have on the amplifier's input for a proper measurement? Is the correct voltage 2.87v RMS?

Also on the max volume i'm getting a stable AC Voltage,am i have to convert this Voltage to Volts RMS?

Thank you very much.
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Old 28th June 2010, 09:30 AM   #2
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
insert a pot between the PC and the amplifier.
Use the pot as an analogue adjustment.
Arrange a -20dB switch (9k & 1k) that outputs just 10% (precisely) of the pot signal and then flick the switch to get full signal.
This is particularly useful when doing power testing when everything gets very hot very quickly.

I would aim for a maximum test signal of 2Vrms switchable to 200mVrms and then the pot to reduce that by a further -40dB giving a range of test signals from 2mVrms to 2Vrms

Keep the PC output near maximum all the time and don't go too high in frequency. The output is far from sinusoidal when frequency rises and digital attenuation is applied.
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regards Andrew T.
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Old 28th June 2010, 09:44 AM   #3
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You just don't know how much i appreciate your instant answer! A big THANKS!
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