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Old 21st October 2013, 08:58 AM   #101
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The only time you'll see a tiny bit of hum from the SYS-2722 analyzer is when measuring the noise floor of very low noise sources using high-res FFTs. I don't recall exact figures, but I think for the unit I'm using the spikes are well below -140 dBu (more like -160/-180 dBu). Unlikely of relevance for THD/THD+N measurements.

Samuel
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Old 21st October 2013, 07:03 PM   #102
RNMarsh is offline RNMarsh  United States
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OK. If I see it, I'll try to be rid of it... one way or another. Other analyzers may not be as clean as the A-P.

-RM
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Old 21st October 2013, 07:56 PM   #103
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Quote:
Originally Posted by Samuel Groner View Post
The only time you'll see a tiny bit of hum from the SYS-2722 analyzer is when measuring the noise floor of very low noise sources using high-res FFTs. I don't recall exact figures, but I think for the unit I'm using the spikes are well below -140 dBu (more like -160/-180 dBu). Unlikely of relevance for THD/THD+N measurements.

Samuel
The 60Hz spikes on mine are below -140dBu, but the noise floor seems only a little lower than -155 dBu
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Old 22nd October 2013, 12:54 PM   #104
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Just checked, 150 Hz is at -146 dBu for both channels. The left channel (closer to the power transformer) shows additional weak signals probably related to mains, so for critical work it might pay off using the right channel.

The -160/-180 dBu I mentioned before is clearly not what it is, I probably remembered these numbers from THD ratio measurements--for a +20 dBu signal -146 dBu is at -166 dB. Yet, hum from the analyzer should not be an issue unless you're working with input signals well below 0 dBu.

Quote:
But the noise floor seems only a little lower than -155 dBu.
This depends on the FFT settings (sampling rate, resolution, window), as the FFT is not scaled for noise. For the measurements I've just done it was around -163 dBu.

Samuel
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Old 22nd October 2013, 01:01 PM   #105
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Samuel, I met Weiss Engineering's boss at the AES last weekend. I mentioned that you are an author for L|A; apparently he thinks very highly of your design and engineering abilities. Can't imagine why

Jan
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Old 24th October 2013, 05:35 PM   #106
KSTR is offline KSTR  Germany
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The issue is becoming weird for me, atm. I tried to see what hum component look like on my 2322 and only found that mentioned same -- and irrelevant -- little 150Hz spike, on the left channel, right channel is clean**), just like Samuel says. But I definitely measured much higher -- but still inside spec -- components (with inputs shorted) on both channels a year ago when I got it, and I personally witnessed the noise levels and the improvement when my colleague did the transformer transplant about 2 1/2 years back. Our lab is in an electrically very noise industrial zone, railroad tracks running along right behind the building, power plant nearby, transformers of various equipment starting/stopping to hum at will (dynamic DC-offsets, probably)... so mabye we were looking at the effect of highly disturbed mains at levels the toroid couldn't handle... will check what the 2722 looks like these days, next...

**) We always see a (non-mains) component at around 80Hz, level depending on time of day (much better in the evenings) which I have not been able to identify or remove yet.
Whish we had a pro mains synthesizer to see if and how much susceptible the AP power supply really is.

Last edited by KSTR; 24th October 2013 at 05:41 PM.
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Old 24th October 2013, 06:30 PM   #107
RNMarsh is offline RNMarsh  United States
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The ac power mains could very well be where the noise is coming in.... the spike.... I routinely apply ac line filtering and ground isolation transformer to test gear (Topaz Ultra-Isolator). Sometimes a quality line regulator as well depending on test/load. Its a habit just from such T&M issues showing up with data in the past.

Thx-RNMarsh
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Old 26th October 2013, 02:35 AM   #108
RNMarsh is offline RNMarsh  United States
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FINALLY! I installed both IM boards yesterday afternoon. Don'task. I am sooo far behind.... Multitasking like crazy to keep up. :-)

Thx-RNMarsh
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Old 28th October 2013, 10:10 PM   #109
RNMarsh is offline RNMarsh  United States
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FINALLY! I installed both IM boards yesterday afternoon. Don'task. I am sooo far behind.... Multitasking like crazy to keep up. :-)

Thx-RNMarsh
Presumably this will fix the #1 priority interrupt that Dolby circuits (a $4-5K option) would try and never let me do what I wanted to do... now they are removed. Part of installing the new IM boards -- remove Dolby.

-RNM
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Old 3rd December 2013, 03:32 AM   #110
RNMarsh is offline RNMarsh  United States
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Thanks to Samuel, I have the A-P running on my WIN8 system :-)
See line # 3253 at Low Distortion Audio Range Oscillator thread.

In a self-test I see -145dB at 2H and 3H on the A-P 2722. This was checked against the ShibaSoku AD725D and they are within 1dB of each other down to at least -130dB... I haven't checked at lower harmonic levels, yet. Expecting close to -150dB, I expect.

Thx-Richard Marsh
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