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Old 23rd April 2009, 08:32 PM   #17771
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Quote:
Originally posted by syn08


Is hum (and other mains frequency harmonics) a form of non harmonic distortion?
Do you mean non-linear distortions of hum?

One mechanism of what I meant, thermal changes of transfer functions by the signal itself, that may contain a hum as well, right.

Are such distortions measurable by ordinary THD measurement procedures?
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Old 23rd April 2009, 08:33 PM   #17772
dimitri is offline dimitri  United States
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Default http://www.aes.org/events/126/papers/session.cfm?code=P27

Quote:
P27-8 Subjective and Objective Evaluation of the Audio Vacuum-Tube Amplifiers—Andrzej Dobrucki, Wroclaw University of Technology - Wroclaw, Poland; Stanislaw Maleczek, Military Institute of Engineering Technology - Wroclaw, Poland; Maurycy Kin, Wroclaw University of Technology - Wroclaw, Poland The subjective and objective evaluation of 5 high-quality vacuum-tube audio amplifiers is presented in this paper. As the reference the professional transistor amplifier has been used. The subjective evaluation has been done by the team of judges as well as with the computer-based psychoacoustic model according with PAQM protocol. The amplifiers’ sound quality assessed by the listeners is consistent with the one evaluated with the use of the psychoacoustic model. It was found that the best sound quality is obtained by vacuum-tube amplifiers, the worst—by the reference amplifier. The results of subjective evaluation are inconsistent with quality assessed by measurement of objective parameters: all amplifiers have comparable quality, but the best is the transistor amplifier because of lowest level of THD+N level.
 
Old 23rd April 2009, 08:54 PM   #17773
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Default Re: Ad797

Quote:
Originally posted by Edmond Stuart


Hi Scott,

Are sure that this is the real schematic (AES preprint 3231, fig. 3a)?
There are a few things that puzzles me and/or makes no sense:

1. Q61, unless the bases of Q3 and Q4 are tied to the collector of Q61 instead of to the collector of Q7.

2. Under normal conditions Q50 is conducting, which spoils the whole thing. If I break the connection between the base of Q15 and the emitter of Q50 the circuit (almost) behaves as expected.
BTW, is Q50 meant to ease the recovery from overloading?

3. Bootstrapping the collector of Q19 instead of Q18. The latter makes more sense as no non-linear Cob loading (by Q18) of the input of the output stage.

Please, see below for my suggested mods and, of course, correct me if I'm wrong.

Regards,
Edmond.

1 and 3 make sense, I need to be at work since I don't have a copy at home. Sometimes clamp devices get drawn in a way that makes no sense.
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Old 23rd April 2009, 09:03 PM   #17774
syn08 is offline syn08  Canada
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Quote:
Originally posted by Wavebourn


Do you mean non-linear distortions of hum?

One mechanism of what I meant, thermal changes of transfer functions by the signal itself, that may contain a hum as well, right.

Are such distortions measurable by ordinary THD measurement procedures?
Yes they are. This is just another non-linearity type (not even new, Self is mentioning about and its pretty famous in IC design, requiring placing the input stage devices on izotherms, etc...).

For the same reasons, an amplifier with excellent THD20 and very poor IMD 19+20KHz (or the other way around) doesn't exist.
 
Old 23rd April 2009, 09:15 PM   #17775
syn08 is offline syn08  Canada
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Default Re: Re: Ad797

Quote:
Originally posted by dimitri
Before even looking at, I may fully agree with the conclusions. Its not even big news, it was previously reported that humas subjectively enjoy distortions (2nd harmonic?).
The problem is to objectively evaluate this kind of preferences and quantify in a general acceptable form. Then engineers could easily pick up and design according to these guidelines.

But I am afraid its going to be pretty hard to set such generally accepted guidelines, for controlled distortions content. As such, it is naïve to imagine that an amp with personalizable distortion content will ever be economically designed and manufactured.
 
Old 23rd April 2009, 09:24 PM   #17776
VivaVee is offline VivaVee  New Zealand
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1audio wrote

Quote:
A spectrum analyzer will only look at content present long enough for it to be seen by the analyzer's technology. Its conceivable that transients could pass through that the analyzer doesn't see. This trick is used a lot to get FCC approval of products that should never have been shipped.
I think this is a very poor example. I believe that you are referring to spread spectrum clocks being used to to spread clock harmonics over a wider than usual spectrum in order to pass the FCC emissions test. Any decent spectrum analyser available in the past 20 years (apart from the cheap garbage based on tv tuners) can see this effect.

The spectrum anlyser is NOT at fault. The FCC test is based on the average signal level in a narrow sweeping band. This is not an example of inadequate equipment but of an outdated mandated test regime. Or rather a perfect example of commercial greed leading to some clever design methods that satisfy the letter of the law while comprehensively breaching the spririt.
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Old 23rd April 2009, 09:58 PM   #17777
PMA is offline PMA  Europe
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Look at DDS output by spectrum analyzer. 3D view would help a bit.
 
Old 23rd April 2009, 10:35 PM   #17778
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I think we are at stage 2: 'It exists, but it is not important' (or something very close to this)

I got a ride in Jack Bybee's Bentley today. What a nice car! 650HP, and all we did was drive local streets. Naim made the auto stereo, and it was pretty good sounding.
 
Old 23rd April 2009, 10:46 PM   #17779
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Quote:
Originally posted by john curl
I think we are at stage 2: 'It exists, but it is not important' (or something very close to this)

I got a ride in Jack Bybee's Bentley today. What a nice car! 650HP, and all we did was drive local streets. Naim made the auto stereo, and it was pretty good sounding.
Jay Leno's car dealer gave me a test drive in a Bentley, I thought it was a little stoggy. He also had an F1 in the shop but it was too expensive to let the riff-raff have at it (1.3M).
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Old 23rd April 2009, 10:53 PM   #17780
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> Naim/650PH

Did you measure the S/N ratio?
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