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Where can I go to use a high end distortion analyzer?
Where can I go to use a high end distortion analyzer?
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Old 8th December 2018, 01:15 AM   #41
chris719 is offline chris719  United States
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Where can I go to use a high end distortion analyzer?
Quote:
Originally Posted by hellokitty123 View Post
I haven't been able to get my amps to produce harmonics above -130db until right at the edge of clipping and I have several variations of the circuit in question which I need to measure in order to optimize the cost and performance. I designed it to be extremely low in noise as far as parts choice and component values go so I'm not worried on that front but I can't really do anything further until I can see the harmonics. Spice suggests that the harmonics are well down into unicorn land but I won't believe it until I see it.
Since the AK4490 DAC in your QA401 can manage -112 dB best case, I suspect all your measurements are lying to you.

If you are serious, just ship a prototype to Tom. Sand the markings off the parts if you must .
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Old 8th December 2018, 01:45 AM   #42
hellokitty123 is offline hellokitty123  United States
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Originally Posted by chris719 View Post
Since the AK4490 DAC in your QA401 can manage -112 dB best case, I suspect all your measurements are lying to you.
I thought we just discussed that the point of averaging was to solve that issue along with the noise floor? Why bother having anything display below -112db if it's a lie?

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Originally Posted by chris719 View Post
If you are serious, just ship a prototype to Tom. Sand the markings off the parts if you must .
What I need right now is quality time in front of a good analyzer so I can finalize optimizations, a one off measurement would not help me much at this stage. A combination of the distortion magnifier, a quality oscillator, and the QA401 should get me where I need to go right?
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Old 8th December 2018, 01:53 AM   #43
Markw4 is online now Markw4  United States
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Quote:
Originally Posted by hellokitty123 View Post
A combination of the distortion magnifier, a quality oscillator, and the QA401 should get me where I need to go right?
Depends what you are building, IMHO. You might look at some sets of measurements they do at Sterephile for different types of equipment. DACs need a different set than power amps, for example.
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Old 8th December 2018, 02:03 AM   #44
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by hellokitty123 View Post
A combination of the distortion magnifier, a quality oscillator, and the QA401 should get me where I need to go right?
Read Cordell's article in Linear Audio #0. It'll answer that question for you.

Tom
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Old 8th December 2018, 02:17 AM   #45
Terry Demol is offline Terry Demol  Australia
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Originally Posted by tomchr View Post
Not true. My Audio Precision APx525 hits -158 dBV noise floor reliably on the analyzer section. Sadly, the analog signal source is considerably noisier.

Tom
Tom,

I'm sure you already know this but just in case -

If the noise 'grass' is on -158dBV that means nothing WRT the RMS noise measurement. With audio we generally use a 20kHz BW. A good example of this are measurements of something like 24bit ASRC. -144dB DR but the noise floor will be around -170dB on a typical FFT.

The only reason you are seeing the grass on -158 is the measurement bandwidth is very narrow = less noise energy.

I learned this very quickly using an old, VHQ analog spectrum analyser. You could keep reducing the sweep bandwidth and magically see the noise floor disappear. Smoke and mirrors!

T

Quote:
Originally Posted by Markw4 View Post
Depends what you are building, IMHO. You might look at some sets of measurements they do at Sterephile for different types of equipment. DACs need a different set than power amps, for example.
They really need to start using a notch filter at the AP IP more often. As gear gets more linear, the AP test set is being challenged. From memory they did this with the Benchmark power amp.

Other frustrating habits are when they measure transformer coupled gear and only do a 50Hz measurement. The transformers LF distortion will dominate. I think JA might be on to this more recently.

T
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Old 8th December 2018, 02:55 AM   #46
jackinnj is offline jackinnj  United States
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Where can I go to use a high end distortion analyzer?
You can drive down to my place in NJ and we can look at it -- but you'll have to bring Christmas cookies or some such bribe to be in my good graces.
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Old 8th December 2018, 03:05 AM   #47
anatech is offline anatech  Canada
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Where can I go to use a high end distortion analyzer?
I normally also suggest that coffee will also help.
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Old 8th December 2018, 03:12 AM   #48
abraxalito is offline abraxalito  United Kingdom
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Hi abraxalito,
That may be, but I wouldn't call that situation a real or useful result.
No disagreement that its a useless number in the absence of a bandwidth.

'A text without a context becomes a pretext'.
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Old 8th December 2018, 03:29 AM   #49
hellokitty123 is offline hellokitty123  United States
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Originally Posted by jackinnj View Post
You can drive down to my place in NJ and we can look at it -- but you'll have to bring Christmas cookies or some such bribe to be in my good graces.
Haha, very tempting! If only I could before Christmas
If that's a serious offer I might be able to take you up on it at some point soon though.
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Old 9th December 2018, 05:42 AM   #50
1audio is offline 1audio  United States
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Where can I go to use a high end distortion analyzer?
Per the spec the APx525 and an equivalent input noise of 1.3 uV or equivalent of 5000 Ohms. That translates into 8 nV/rtHz. The best instruments are around 5 nV/rtHz.

Using FFT's you can see noise and artifacts well below that limit with high resolution FFT's. Still oscillators capable of harmonics below -130 dB are limited. Victor's would be the go to solution and very cost effective. The QA401 is really very good. Not quite an RTX but still very low distortion and very useful for this stuff. It uses the same DAC and a wider band ADC that has a higher distortion floor. On both you need to keep the levels about -15dBFS for lowest distortion.

The THX stuff is a bit of an outlier since they have focused on ultra low distortion for some time. Those measurements showing a harmonic at -140 dB from a headphone amp are not done with commercial equipment. AP can tweak an APx525 for around -120 dB THD+N but that is a hybrid analog/digital instrument. I can get there with a Victor oscillator and a Shibasoku 725. And the combination can just hit -140 dB on harmonics typically.

When the system and the DUT have similar harmonic levels they can add or subtract with big errors. If they are out of phase the level goes to zero. In phase then it goes up 6 dB. This is why the system needs to be significantly better than the DUT.

I can get to -170 dB with the CLT-1 but its a single frequency device generating 10 KHz and measuring 30 KHz.

The distortion magnifier will get you further when checking a linear amplifying stage. If everything else is optimal you can get pretty good results. Hopefully it will show what you want to see.

I would be happy to put your device on the bench if you want. PM me. It would force me to clean up the benches.
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