# How to measure amplifier's Freq. resp.?



## leoparleur (Oct 9, 2010)

Hi,

I am new in this forum and would like to know if I can measure my amp's frequency response with REW. I've been searching for a few hours and haven't found any answers except maybe using a attenuator.

Is there a guide somewhere to help me out carry this mesurement? If not, can someone help out.

Thanks! :0)


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## JohnM (Apr 11, 2006)

The big risk is blowing up the soundcard input, hence the need to use an attenuator to reduce the output levels from the amplifier. Do you have a particular reason to doubt the amplifier's frequency response?


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## leoparleur (Oct 9, 2010)

Hello John,

First, thanks for helping. Not that I have a problem with it, I only want to validate the difference between my SET tube amp compared to a Pass Labs First Watt. I want to look more into details how my 6550 tubes emphasis in the mid and bass compared to the F1. If possible, I'd really be happy to also measure distortion at different wattage.

Could you or a member guide me to make such measurement?
Is there a procedure written somewhere I could use as a reference?

Kind regards.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Basically it would be the same as the sound card calibration routine. John mentioned you’d need an attenuator. If the amp has gain controls, that will work. If not you could connect a pre-amp in front of the amp and it could be your attenuator. Or, you could connect an L-pad in the output line (speaker wires). In any event, you’d start with the level fully attenuated, then bring it up just enough to get the appropriate readings on the REW input meters.

Regards,
Wayne


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## leoparleur (Oct 9, 2010)

Hi Wayne,

Thanks for your input. The First Watt doesn't have volume control, my tube amp does.

So not to take any chance, if not using preamp on First Watt what do you recommend as L-pad attenuator?

To make a fair comparaisons I guess I need to set and measure output voltage to same levels for both amp using REW or MS Win. The software setting will be different from the 2 amps. I also understand that I need to be very carefull on level so not to overload card input, it could fry it. I assume I need to have a dummy load connected and connect from that cable to the card's input, right?

If I decide to put preamp in the signal chain for measuring First Watt, I will need to redo system calibration including this unit compared to the tube amp.

Secondly for my integrated amp, in REW, is it doable to measure distorsion versus different power ratings? I guess this will necessitate a particular jig in this situation.

Thanks!


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