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Old 22nd January 2012, 09:52 PM   #11721
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The 3rd harmonic is dependent on the amount of cancellation of 2nd
harmonic, so it is possible to see reduce 3rd in the presence of greater 2nd.

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Old 23rd January 2012, 05:41 AM   #11722
Dzius is offline Dzius  Poland
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I used computer as a source, recording and FFT analysis tool.
More specific Audacity program: Audacity: Download for recording and analysis, and Windows Mediaplayer for playing 1kHz signal generated in Audacity.

So there is a chance that spectra are not so fabuluos duo to computer soundcard distortion. Nonetheless it can be used to trim amplifier.
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Old 23rd January 2012, 01:05 PM   #11723
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When you run any kind of FFT or analog "narrow bandpass" scan it's useful to establish a couple of baselines -- you can short the RCA's on the input and see whether you're picking up interference from a power supply, video card etc, you can connect the test leads and terminate them in a 50R load and see how much interference is picked up by the cabling. Generally, if these unhelpful artifacts are 30% or less of the fundamental the RMS'ing works out such that you're better than 2-sigmas.
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Old 23rd January 2012, 01:26 PM   #11724
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Default Lower value of one source resistor

Hi,

I know that official F5 amp has one source resistor 0.47 Ohm and other is 0.39 hm (0.47 + 2.4 in paralell). How do I determine which resistor should I lower? The one that is connected to mosfet with higher transconductance?
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Old 23rd January 2012, 06:01 PM   #11725
lykkedk is offline lykkedk  Denmark
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Hello...

I am trying to build a F5, for the hole lot FUN of it

Do i benefit anything, "pairing / matching" the Q1 vs. Q2 to each other ??? (2sk170bl / 2sj74)

Jesper.
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Old 23rd January 2012, 06:14 PM   #11726
Dzius is offline Dzius  Poland
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So that's the noise floor.
Noise.jpg
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Old 24th January 2012, 10:55 AM   #11727
xenob is offline xenob  Austria
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Hi Dzius: nice distortion pics.

I recently discovered ARTA and used it to set up my BA-3.
It shows you THD and THD+N in %.

Next thing to do do is check distortion vs frequency (Farina method or in STEPS).
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Old 24th January 2012, 01:01 PM   #11728
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Quote:
Originally Posted by Dzius View Post
So that's the noise floor.
Attachment 262017
Try with the input shorted -- I ran this test a half-dozen times to make sure my eyes weren't fooling me -- although I believe that the numbers below 30Hz or so are bogus as they are well below the threshold of the SYS2722. This is noise referenced to 0dBV.

Bottom graph is an F5 connected to the analyzer, but not to the a.c. line, second test is connected to the power line, but not "ON", third is with the F5 on.
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Old 24th January 2012, 03:24 PM   #11729
AndrewT is offline AndrewT  Scotland
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Better than -100dB ref 1Vac (0dBV)?

That's equivalent to no individual frequency giving more than 10uVac at the output.

Adding all the frequencies together would give the total noise at the output. Expect <100uVac

I am surprised there is no 3rd harmonic of the 60Hz mains.
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Old 24th January 2012, 04:48 PM   #11730
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Quote:
Originally Posted by kacernator View Post
I know that official F5 amp has one source resistor 0.47 Ohm and other is 0.39 hm (0.47 + 2.4 in paralell).
I am unaware of this being the official circuit.

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