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Old 13th December 2012, 01:05 AM   #1111
RNMarsh is offline RNMarsh  United States
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Comparing specs from Audio instrument makers ($$) --- SRS model SR1 the residual thd+n is spec'ed at -106 to -112dB. The AP 2700 is spec'ed at -112 to -115dB. I want better, unfortunately. Thx-RNMarsh
Noise floor (22KHz BW) is -118dB spec on the SRS. Now there is some fudging going on with both examples... like using 3-4 volts of output as ref. In any event, it looks like < -120 is pushing things pretty hard in analog domain for wideband sources/testers. -RNM
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Old 13th December 2012, 01:22 AM   #1112
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Originally Posted by RNMarsh View Post
Comparing specs from Audio instrument makers ($$) --- SRS model SR1 the residual thd+n is spec'ed at -106 to -112dB. The AP 2700 is spec'ed at -112 to -115dB. I want better, unfortunately. Thx-RNMarsh
The Christmas tree bulb was better than that out of the box.
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Old 13th December 2012, 01:25 AM   #1113
1audio is offline 1audio  United States
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Hi Demian -- something isn't correct here -- I RMSed the first 9 products using my little Excel worksheet and got 0.00035%, -109dB. I assumed that the fundamental was at 0dBFS. If it is lower, and it seems to be lower than -4dBFS, then the THD is even higher than I calculated.

Edit -- with fundamental at approx -5dBFS, the THD is -104, 0.00064%
You are right, the calculation is off somewhere. I got different numbers the second time I tried it. Beta software. . .

Can you post a link to the spreadsheet?

My point was that the broadband noise can make even really low numbers not so low. And the THD+N meters (any of these older units) only measure the combination.
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Old 13th December 2012, 01:28 AM   #1114
1audio is offline 1audio  United States
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Originally Posted by scott wurcer View Post
The Christmas tree bulb was better than that out of the box.
Here is an idea, use a DC voltage added to the AC across the bulb to steer the absolute output level.
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Old 13th December 2012, 03:16 AM   #1115
davada is offline davada  Canada
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Here is an example of THD vs. THD+N. This is a measurement of my KH4400A. The THD is -117 dB/ .00013% but THD+N is -97/.0014%, a 20 dB difference and the noise floor is in fact quite low. Its just the effect of the energy inside the frequency band.

I will collect the different protection solutions I have docs for and we can see what there is to learn. There are anumber of different tricks used in different products. To meet the CE spec most measurement instruments need to be able to withstand something like 300V without damage (or becoming a hazard to the user) so there are a lot of good solutions.
Hi Demian,

What OS are you running QA400 on?
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Old 13th December 2012, 03:19 AM   #1116
richiem is offline richiem  United States
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Default Excel spreadsheet for THD calc

Not sure this will download for use successfully, but it's worth a try. I left the last run of numbers in to give an example.
Attached Files
File Type: zip THDcalc.zip (5.5 KB, 25 views)
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Old 13th December 2012, 03:21 AM   #1117
davada is offline davada  Canada
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Originally Posted by richiem View Post
Hi Demian -- something isn't correct here -- I RMSed the first 9 products using my little Excel worksheet and got 0.00035%, -109dB. I assumed that the fundamental was at 0dBFS. If it is lower, and it seems to be lower than -4dBFS, then the THD is even higher than I calculated.

Edit -- with fundamental at approx -5dBFS, the THD is -104, 0.00064%

I't works out to .000607% THD.
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Old 13th December 2012, 03:49 AM   #1118
1audio is offline 1audio  United States
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Hi Demian,

What OS are you running QA400 on?
Win 7 64 on I5 w/ 6 GB of ram.

I'll try it on the other systems in the next few days. It seems to crash a lot on this system.
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Old 13th December 2012, 03:59 AM   #1119
RNMarsh is offline RNMarsh  United States
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Originally Posted by scott wurcer View Post
The Christmas tree bulb was better than that out of the box.
that one and several others as well. Whats up with these companies not being SOTA in lowest harmonic distortion attainable... and at their prices, too?? [no need to answere] -RNM
When I used the thd+noise instrument from Demian, it was reading on my little amp... .0005% . Too close to the test equip residual? The FFT output was uncalibrated so that didnt help. can it be easily/accurately calibrated? Looking for a test system to easily and accurately measure harmonics in the .00001 - .0001% area. Thx-RNMarsh

Last edited by RNMarsh; 13th December 2012 at 04:17 AM.
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Old 13th December 2012, 04:08 AM   #1120
davada is offline davada  Canada
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Win 7 64 on I5 w/ 6 GB of ram.

I'll try it on the other systems in the next few days. It seems to crash a lot on this system.
Smoking.

What version of software do you have?
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Last edited by davada; 13th December 2012 at 04:11 AM.
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