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Old 8th March 2014, 05:23 PM   #1
2wice is offline 2wice  South Africa
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Default Balanced attenuator testing

Hi all

Would it be possible to test two types of attenuators with a function gen and scope, to measure which one performs better?

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Old 8th March 2014, 05:40 PM   #2
DF96 is offline DF96  England
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You need to define 'performs better'. If you mean more precise gradation of attenuation or flat frequency response then probably yes. If you mean low distortion or low noise then probably no - a scope is far too crude an instrument for seeing the very low levels of noise and distortion from any competent attenuator or pot.
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Old 9th March 2014, 03:37 PM   #3
2wice is offline 2wice  South Africa
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Thanks very much.

What equipment would then be used to measure distortion or low noise?
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Old 9th March 2014, 05:26 PM   #4
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hi.
You'll need some expensive gear such as Audio THD analysers etc. That saying, a passive attenuater wouldn't create any audible noise. No distortion if designed correctly with the proper impedances.
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Old 9th March 2014, 10:59 PM   #5
DF96 is offline DF96  England
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I am always mystified why people make such a fuss about a simple potential divider.
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Old 9th March 2014, 11:26 PM   #6
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Well, some of them aren't very good, sometimes more distortion than an amplifier!
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Old 9th March 2014, 11:56 PM   #7
DF96 is offline DF96  England
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I'm not sure how you could arrange an attenuator to have worse distortion than an amp, since they use the same technology (resistors) to set attenuation and gain respectively. One exception might be LDR controls, as they are known to be non-linear (but surprisingly popular with some people).
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Old 10th March 2014, 12:09 AM   #8
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In this case, it was the gain pot of a mike amp I was testing on an AP2322. The pot became slightly dodgy, and distortion went up 20dB. Tapping and operating the pot brought it back down, but what if you didn't notice?

Sure, pots are icky, but still, it is an 'attenuator' made only of resistance materials. The point is that not all ways to do this are always good.
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Old 10th March 2014, 12:13 AM   #9
DF96 is offline DF96  England
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Ok, a faulty pot can add distortion.
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Old 10th March 2014, 12:44 PM   #10
2wice is offline 2wice  South Africa
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Apologies for all the noob questions. I'm trying to learn.

In what way does impedance mismatch effect noise /distortion?

Say I have [source-->DCB1-->20k attenuator-->Focal CMS65(Amp rated 20k)]

ie: What happens if attenuator is rated lower or higher than the amp?

In my current design I cannot find exact matches for the resistors, the range will be about 18k to 22k.

For interest sake what would happen if it was 100k?
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