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Old 20th April 2012, 02:46 AM   #4531
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The top one was the classic 1kHz signal. You mean noise measurements like this?

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Last edited by SoNic_real_one; 20th April 2012 at 02:49 AM.
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Old 20th April 2012, 02:49 AM   #4532
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Old 20th April 2012, 02:57 AM   #4533
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Quote:
Originally Posted by SoNic_real_one View Post
The top one was the classic 1kHz signal. You mean noise measurements like this?
No, but rather spectra of the output response to the test signal at several points on the upslope with decreasing power part of the curve.
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Old 20th April 2012, 03:01 AM   #4534
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Probably it would worth investigating more...
For me, the fact that the first amp (MBL 9011) is 10 time less than the HK990 (good SNR also), makes me think that the noise is not the issue there.

I don't use amplifiers so low, I think I am at minimum 2-5W usually. If I need to go below that (night, family), I have the headphones.

Last edited by SoNic_real_one; 20th April 2012 at 03:04 AM.
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Old 20th April 2012, 03:16 AM   #4535
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That kink just above 10W is the AP range changing - means the DUT is beating the AP, nice one Which amp is it?
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Old 20th April 2012, 06:58 AM   #4536
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.0001W. Yea right. In the noise. Is .01 watt valid? ONE watt would be. Going for a standard 10X resolution, start at .1W. I think it was mentioned a few thousand posts ago of an Italian mag that tested at many powers across the spectrum and produced a nice 3-d waterfall plot. That would be insightful information. It still leaves out the difference in amps in proportion of high to low order harmonics and if that changes across the spectrum or with power. We need at least a four dimensional plot. Frequency, power, distortion, ratio high to low. We need to be able to slice the plot on any axis. If you have the data, Matlab can do the plot.
Yes, Italy's SUONO (Sound) magazine went into 3D power plots from roughly -5 to +3 dB relative to nominal declared power output into 8 Ohms.

I remember sseing that HK 2400 power amp did particularly well, signs of disturbance started to appear at around +1 dB. Marantz's model 80 power amp also did well, and, not surprisingly, Nakamichi's Stasis amp did well.

By contrast, UK's Musical Fidelity nominally working in class A (when in fact it simply uses higher bias, far from true class A) did especially poorly, as it was breaking up at -4 dB.

The graph looks very much like a loudspeaker waterfall graph. As far as I am aware, they were the first to use such graphs, but then, they have always been at least cut above all others I have ever seen since the mid 70ies. They were tightly connected to Rome's IAF (Instituto Alta Fedelita) and had measurements like no other magazine, but also pioneered the combination of objective and subjective in their tests.

Frankly, they were at least 10 years ahead of all others I have ever seen.

But, magazines are created and staffed by people. All that was achieved by one set of people, and when they disbanded during the mid 90ies, the mag was never quite the same quality again. Today, it's just a reminder to older readers of what it once used to be.
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Old 20th April 2012, 07:16 AM   #4537
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"My name is Steve Keiser, the 'K' of B&K components, [snip]- Steve Keiser
Wayne do you have a link to this or is it personal communication?
Can't find it on the 'net.

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Old 20th April 2012, 07:24 AM   #4538
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A long, long time ago, in a galaxy far, far away ...

We used to see graphs like the ones shown even in ads (e.g. Sansui 9900 and 11000 ad sheets).

It was called "distorion comeback".

Then somebody discovered that if you give your output stage a little more bias current than the usual 20-30 mA as the Japanese industry did, this effect seemed to subside quite considerably (although it didn't conveniently disappear)

By comparison, the European production was always on a higher level, typically 40-80 mA, most being in the 50-60 mA range, but most European production models were made for nominal 4 Ohm loads.

I've played with this quite a lot over the years. I found that up to a point, there will be favorable effects you can hear, and after that point, you can add all thebias you want to, nothing favorable will happen. In fact, in some cases, you will experience a certain dulling of the sound, a loss of focus, so to speak.

In my experience, you get what there is to be gotten out of it by about 130 mA per output device. Thus far, I have not come across an amp which benefited from more than that, but I have seen and heard amps which had their limit of improvement at a lower point, like 110-120 mA per output device.

I should also note that only plain, old THD was investgated.
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Old 20th April 2012, 10:00 AM   #4539
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Originally Posted by janneman View Post
Wayne do you have a link to this or is it personal communication?
Can't find it on the 'net.

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Old 20th April 2012, 11:12 AM   #4540
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I seem to recall it was in an interview of Keith Johnson in The Abso!ute Sound, many years ago, but I could be mistaken. I do recall he remarked about the large number of charge carriers involved in a tube versus silicon devices.
Just trying to understand this. Wouldn't the opposite be true, since tubes usually operate at much higher voltages than silicon, and so I would presume use less charge carriers to achieve the same power output?
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