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Old 13th December 2012, 05:31 PM   #7821
bcarso is offline bcarso  United States
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Quote:
Originally Posted by a.wayne View Post
Krell ......!

Krell Full Power Balanced 350mc monoblock amplifier Measurements | Stereophile.com


This is a very quiet amplifier, with an A-weighted S/N ratio of more than 95dB. This is referenced to 2.83V output; this is equivalent of more than 130dB referenced to the amplifier's clipping point into 8 ohms! Even without the A-weighting network and extending the measurement bandwidth to 500kHz only worsened the S/N ratio to 84dB (again re. 2.83V).

Levels of harmonic distortion were also very low, particularly into higher impedance loads. The bottom trace in fig,3, for example, was taken at 2.83V into 8 ohms, and doesn't vary from 0.005% across the band. Reducing the load to 4 ohms increased the THD figure slightly to 0.007%, though into 2 ohms, the distortion went up to 0.03%.
There you go --- that's quite respectable, even with A-weighting. About 50uV rms at the output. Now the assumption there is that no hum etc. is going to come in at the higher powers to spoil the extrapolated >130dB. But still, these are numbers that should be, and apparently in this case are, achievable.

HFN/RR may have botched the measurement on the new stuff. Or did D. d'A. part company due to a philosophical disagreement? (I doubt it).

Thanks for digging up that reference. I was just on the verge of doing a search.
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Old 13th December 2012, 07:51 PM   #7822
dvv is offline dvv  Serbia
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Originally Posted by DF96 View Post
Yes, this is where 'everybody knows' perhaps clashes with physical reality. Unbypassed caps need low ESR for low total impedance. Bypassed caps need somewhat higher ESR for low total impedance. Even simple circuit theory can be counter-intuitive.
You said it, DF96.

As my late grandma used to say, we live and learn all our lives, yet we still die foolish.

Then again, to me at least, that was a delicious piece of info. The thing is, I love learning, and when something like that sort of unexpectedly flies in my face, I just thrive on it. That bit of info really made my week, I'm still mulling it over.

It's all like a big jigsaw puzzle and I'm enjoying putting it together.
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Old 13th December 2012, 07:58 PM   #7823
dvv is offline dvv  Serbia
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Quote:
Originally Posted by bcarso View Post
There you go --- that's quite respectable, even with A-weighting. About 50uV rms at the output. Now the assumption there is that no hum etc. is going to come in at the higher powers to spoil the extrapolated >130dB. But still, these are numbers that should be, and apparently in this case are, achievable.

HFN/RR may have botched the measurement on the new stuff. Or did D. d'A. part company due to a philosophical disagreement? (I doubt it).

Thanks for digging up that reference. I was just on the verge of doing a search.
That same magazine did a test of Krell amps during the 90ies, specifically by Martin Colloms. He mildly criticized Krell for producing like 0.3% into 4 Ohms at rated power, 20 Hz to 20 kHz, I remember that distinctly.

Unfortunately, I don't remember the exact model under test, it's been some 14 years ago, or more.
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Old 13th December 2012, 08:39 PM   #7824
KSTR is offline KSTR  Germany
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Some network analyser shots from today (first realistic measurements) :


1000uF/63 PanaFC + 220nF Wima MKS2 (upper trace) vs.
1000uF/63 PanaFC + 220nF Wima MKS2 + 3.3uF Wima MKS2 :
Click the image to open in full size.
The PanaFC has seen some minutes of forming then some rest time to droop DA residual voltage of ~300mV after charging to 40V.

Vertical scale is dB ref 1 Ohm, so -20dB is 0.1Ohm etc.
The 1000uF should give 0.16Ohms at 1kHz --> -16dB, -14dB actual, OK.
ESR is at -28dB which amounts to 40mR, on spec too, fine.

With 220nF impedance peaks to over 0.3Ohms at 2Mhz. Paralleling the 3.3uF Wima MKS shows more wiggling but overall impedance stays below 0.1Ohm up to 8Mhz. It's seen that an impedance variation of more 10:1 can happen easily somewhere in the lower MHz frequencies.


Effect of a few cm of wiring forming some little loop inductance vs. shortest possible connection of the probe (and only 220nF bypass this time) :
Click the image to open in full size.
We can see the slight increase of ESR as well as a quite diminshed effect of the bypass and a 15dB (6x) increase of impedance above 4Mhz.


Physical setup showing the less than optimum connection with probe leads not right at the caps (shown with 3u3uF bypass) :
Click the image to open in full size.
Attached Images
File Type: jpg 1000uF_panaFC+220nMKS+-3u3MKS.jpg (212.2 KB, 206 views)
File Type: jpg 1000uF_panaFC+220nMKS_long_vs_short_leads.jpg (203.8 KB, 200 views)
File Type: jpg 1000uF_panaFC+3u3MKS_imp_setup.jpg (53.6 KB, 109 views)

Last edited by KSTR; 13th December 2012 at 08:45 PM.
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Old 13th December 2012, 09:25 PM   #7825
bcarso is offline bcarso  United States
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Quote:
Originally Posted by KSTR View Post
Some network analyser shots from today (first realistic measurements) :


1000uF/63 PanaFC + 220nF Wima MKS2 (upper trace) vs.
1000uF/63 PanaFC + 220nF Wima MKS2 + 3.3uF Wima MKS2 :
Click the image to open in full size.
The PanaFC has seen some minutes of forming then some rest time to droop DA residual voltage of ~300mV after charging to 40V.

Vertical scale is dB ref 1 Ohm, so -20dB is 0.1Ohm etc.
The 1000uF should give 0.16Ohms at 1kHz --> -16dB, -14dB actual, OK.
ESR is at -28dB which amounts to 40mR, on spec too, fine.

With 220nF impedance peaks to over 0.3Ohms at 2Mhz. Paralleling the 3.3uF Wima MKS shows more wiggling but overall impedance stays below 0.1Ohm up to 8Mhz. It's seen that an impedance variation of more 10:1 can happen easily somewhere in the lower MHz frequencies.


Effect of a few cm of wiring forming some little loop inductance vs. shortest possible connection of the probe (and only 220nF bypass this time) :
Click the image to open in full size.
We can see the slight increase of ESR as well as a quite diminshed effect of the bypass and a 15dB (6x) increase of impedance above 4Mhz.


Physical setup showing the less than optimum connection with probe leads not right at the caps (shown with 3u3uF bypass) :
Click the image to open in full size.
Can you rig up the ground reference for the scope to eliminate most of the ground lead? It may be a contributing factor in the measurement.
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Old 13th December 2012, 09:32 PM   #7826
DF96 is offline DF96  England
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Quote:
Originally Posted by dvv
As my late grandma used to say, we live and learn all our lives, yet we still die foolish.
Your grandma must have been hewn from the same block as my grandma - that is the sort of thing she would have said!

The trick to remember about series-parallel components is that you get a form of inversion when converting from series to parallel or back again. Put a small resistor in series with a cap. Convert to parallel form at a particular frequency: you get a cap of almost the same value, but a parallel resistor with a big value. Make the small series resistor smaller, and the big parallel resistor gets bigger. The same thing happens if you replace the cap with an inductor. Put a cap and inductor in parallel and at resonance you see the big parallel resistor, not the small series resistor. The inductor is of course the big component which you bought as a capacitor.

What is more, the parallel resistor can vary like the square of the frequency or the inverse. This effect does not seem to be widely known, even among experienced engineers and academics.
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Old 13th December 2012, 10:22 PM   #7827
KSTR is offline KSTR  Germany
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Originally Posted by bcarso View Post
Can you rig up the ground reference for the scope to eliminate most of the ground lead? It may be a contributing factor in the measurement.
Yes, that is uncontrolled factor as of yet. I plan to repeat measurements with a fully compensated setup on the weekend, cutting a short BNC interconnect in the middle and feeding the 75R input directly, as I figured out I won't need the high-Z probe with the suboptimal GND clip for the purpose. Also I'll do a check witha true low inductance 1R reference resistor instead of the 10R 0207 I used, a 1206 film chip type should hopefully be OK up to at least 10MHz. I'm still on a steep learning curve of using a network analyser, let alone at MHz freqs.
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Old 13th December 2012, 10:45 PM   #7828
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Leads are too long.
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Old 14th December 2012, 06:47 AM   #7829
dvv is offline dvv  Serbia
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@KSTR

Many thanks for your time and trouble. This is exactly what I asked about, I certainly didn't expect you to run out and buy some F&T large caps.

As John pointed out, the leads are much longer here than they would be if it was properly soldered to a circuit board. Which I believe would probably drop the overall value down a bit across the board, but I don't think it would change the curves significantly. Of course, I could be wrong.

This is of particular interest to me simply because these would be almost exactly the same values, only I assumed 2.2uF Wima MKS, no particular reason, it just seemed right. I assumed the size difference between the first (100uF) and the next (2.2uF) should be bigger than between the second and the last (100nF).

Again, no particular reason, it just seemed right.
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Old 14th December 2012, 06:58 AM   #7830
dvv is offline dvv  Serbia
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Quote:
Originally Posted by DF96 View Post
Your grandma must have been hewn from the same block as my grandma - that is the sort of thing she would have said!
Most probably so, DF96. Those older folks were made sturdier than the kids of today, and they had no Tweeter or Facebook, they had to learn about life first hand. And life wasn't too kind to her, but that's another story.

Quote:
The trick to remember about series-parallel components is that you get a form of inversion when converting from series to parallel or back again. Put a small resistor in series with a cap. Convert to parallel form at a particular frequency: you get a cap of almost the same value, but a parallel resistor with a big value. Make the small series resistor smaller, and the big parallel resistor gets bigger. The same thing happens if you replace the cap with an inductor. Put a cap and inductor in parallel and at resonance you see the big parallel resistor, not the small series resistor. The inductor is of course the big component which you bought as a capacitor.

What is more, the parallel resistor can vary like the square of the frequency or the inverse. This effect does not seem to be widely known, even among experienced engineers and academics.
In your view, how would the following work: 1st power input cap 100 uF, second in // 2.2 uF metallized foil, // 01, uF metallized foil, // 1R/2W metal film resistor in series with low inductance in series with 0.47 uF metallized?

Theoretically, the 1R+470 nF to the ground should rid the circuit of stray inductance. I ask because as you pointed out, on occasion it can all be counterintuitive.
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