John Curl's Blowtorch preamplifier part II - Page 2318 - diyAudio
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Old 18th May 2012, 04:10 PM   #23171
Bonsai is offline Bonsai  Taiwan
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Well, I'll for sure continue skipping the CC's!
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Old 18th May 2012, 04:34 PM   #23172
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Well Ed Simon, you have made it very clear why we have to take care as to what feedback resistor we use.
Just to remind everybody, I have been 'harping' about differences in resistors for more than a decade, especially with the feedback resistor, as it is the 'template' that the amp tries to model itself on. Usually to much 'laughter' as well. Well, now it should be clear, VERY clear. '-)
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Old 18th May 2012, 04:53 PM   #23173
jcx is online now jcx  United States
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but you say you don't find bulk metal foil - arguably the technical best to be the audible best - hows that square with you "I never add distortion" claim?
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Old 18th May 2012, 05:00 PM   #23174
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Originally Posted by simon7000 View Post
Demian,

BTY if you know of any -140 db amplifiers I'd be curious. (-140 IM @ say 1KHz -30 and .03 Hz -3.)

ES
Ed,

Can you be more specific here? Maybe I missed something. Are you talking about a power amplifier? What kind of IM are you talking about? Two tone? SMPTE? Or did you mean to be talking about 1 kHz THD?

Cheers,
Bob
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Old 18th May 2012, 05:28 PM   #23175
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Originally Posted by scott wurcer View Post
GASFET's do fine,IEEE Xplore - Abstract Page

20K noise temperature at 500MHz not bad.
There's a company that has been testing and categorizing silicon for dc to dc conversion at 77k. Power as well as smart stuff. The purpose of conversion at 77k is to eliminate the warm to cold transition heat loss of very large copper conductors required for 5 or 10 kiloamp operation. If they can use a kilovolt or 2 and drop the current to 50 amps, the refrigeration expense goes down.

John
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Old 18th May 2012, 05:33 PM   #23176
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Now you know why I prefer cheap as dirt Russian military MLT, C2-22, C2-23 resistors...
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Old 18th May 2012, 05:42 PM   #23177
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Originally Posted by Bob Cordell View Post
Ed,

Can you be more specific here? Maybe I missed something. Are you talking about a power amplifier? What kind of IM are you talking about? Two tone? SMPTE? Or did you mean to be talking about 1 kHz THD?

Cheers,
Bob
Bob,

IM dual tone, one at .03 Hz at a power level of -3db re full power, the other 1 KHz around -30db re full power. Just for you you can also try it at 20 KHz.

Yes I meant a power amplifier. Now most can't handle .03 Hz so you may have to run up the frequency a bit, but that will result in lower distortion.

The issue I have been playing with as shown by the two measurements of the same resistor comparisons is that the envelope of a musical note (often mentioned as ADSR) can cause shifts in amplifier performance. The question has become, are there forms of transient distortions (ex. once every 1000 seconds!) that are missed in testing but are large enough to be detected by an experienced listener?

ES

And just to be a B... show the same levels of distortion at the real operating point say one watt!
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Old 18th May 2012, 05:45 PM   #23178
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but you say you don't find bulk metal foil - arguably the technical best to be the audible best - hows that square with you "I never add distortion" claim?
Others measure better on third order distortion. Low tempco is nice low and linear is better.
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Old 18th May 2012, 06:11 PM   #23179
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Originally Posted by simon7000 View Post
As you can see from this 19 & 20 KHz IM plot, it is the low frequency modulation that makes the CC & MF perform significantly differently.
Simon,
I find it difficult to interpret measurements in your second picture.
After zooming in, one can see that yellow trace is always underneath the red one, which means almost the same spectral content.
Yellow trace shows, what appears to be, higher noise floor in 20Hz-1kHz region, but according to text notes, yellow is MF. Is that correct?

Best,
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Old 18th May 2012, 06:14 PM   #23180
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Originally Posted by elektroj View Post
Simon,
I find it difficult to interpret measurements in your second picture.
After zooming in, one can see that yellow trace is always underneath the red one, which means almost the same spectral content.
Yellow trace shows, what appears to be, higher noise floor in 20Hz-1kHz region, but according to text notes, yellow is MF. Is that correct?

Best,
That is correct. Although they seem to be about the same below 40 and back by 250 Hz.

Last edited by simon7000; 18th May 2012 at 06:18 PM.
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