# REW testing Amplifier?



## thaumas (Nov 6, 2012)

Hi everybody!

I was wondering if with REW we could also test the transparency of an amplifier? I'm using a Zoom H4n as a sound card, so the idea would be to just send the signal sweep from REW then it will flow through the previously calibrated sound card, into the amplifier and it would come back into the mic and finally analyze by REW. Knowing that the mic level entry would be set somewhere near the minimum. 
Is there something wrong with this? I know enough to know that I don't know enough to assume this will work, So if you've got any insight, please feel free to share, I'm eager to know.

Thanks anyway 
Thaumas


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## fusseli (May 1, 2007)

I don't really see the point? Amplifiers are designed to be transparent and unless it's of very low quality or has tone or EQ controls (or built in) it's almost certain to play flat.

I haven't heard of anyone testing an amp with the method you describe. It would be a risk of frying your soundcard and/or computer with your amp, I'm not sure if you could get the level low enough to look like a line-in signal but maybe it's possible...


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## thaumas (Nov 6, 2012)

Well actually I just got some old amplifiers I wanted to know how good they were/are. They are at least 15 or 20 years old or maybe more so I think the question about linearity is relevant. If you set the gain of your amplifier to the minimum and slightly increase the volume of the amplifier I should not fry my sound card? Or if I'm wrong please tell me?

I think it could also be a good idea to test a Bose amplifier to know more about the specific sound that people are talking about?

Thanks for you response! 
Thaumas


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## EarlK (Jan 1, 2010)

Google "Testing Electronics" for some inspiration . Then buy a book or two ( from Amazon.com, etc. etc. on testing circuits .



Give yourself a month or two to absorb all the info ( before hooking your soundcard up to the output of an amplifier ) .

Make sure that you research, how to make ( & use ) gain dropping pads .

Doing all this should save you the heart-ache of burned out computer components .

If you get bored with learning & simply move your attentions on to other important matters / well,,, that'll work just as well .

:sn:


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## thaumas (Nov 6, 2012)

Thanks earlK, I'll look into it! :T 
Thaumas


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## fusseli (May 1, 2007)

I wouldn't be the least bit surprised if there was compensation (EQ) built into Bose amps that are sold as packages with speakers. They and others have been known to make speakers with FR that appeals to the intended audience's ear rather than produce flat FR. Usually most amps designed for any speaker, like AVRs, PA amps, car amps, will have tone or EQ controls if the amp has the ability, and have an essentially flat FR that is band limited to the audio spectrum.


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## AudiocRaver (Jun 6, 2012)

With REW you can do frequency response and distortion measurements for a quality check on an unknown amplifier. Impulse and step responses should be very fast and clean. These are basic measurements, tell you if an amp is working properly or not.

The devil is in the details of how to go about it. Be careful not to fry your sound card.


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## thaumas (Nov 6, 2012)

Thank you AudiocRaver! It was the answer I was looking for! I'm going to read some stuff about the maximum input of my soundcard, and I will try it from there. or I'll try to find a cheap sound card for this purpose 'cause thanks to REW it will correct it  

Merry christmas to you all!
Thaumas


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## informel (Jun 21, 2011)

thaumas said:


> Hi everybody!
> 
> I was wondering if with REW we could also test the transparency of an amplifier? ...
> Knowing that the mic level entry would be set somewhere near the minimum.
> ...


The voltage out of the amplifier would be too much for the input of the sound card.
I would use a a voltage divider using 2 resistances. 

If you speakers are still connected you cna use 2 resistances in series like 1 ohm and 100 ohm and you connect the input across the 1 ohm.

If you disconnect the speaker, then the sum of the sum of the resistance should aproximate the load of your speaker you could use a .1ohm and a 56 ohm, it does not have to be 8 ohm ( your speaker impedance are not a constant 8 ohm).


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