John Curl's Blowtorch preamplifier part II
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jneutron
diyAudio Member

Join Date: Jan 2004
Location: away
Quote:
 Originally Posted by DF96 Proximity effect is just the mutual version of skin effect (i.e. self-proximity). Skin effect is linear, therefore proximity effect is too.
Think of it within the context of figure 3. The loop area modulation and therefore the resistance, is a function of the absolute value of the current slew.

Proximity effect modulation of a cylindrical resistor's resistance is a function of the absolute value of the current derivative.

jn

 10th January 2013, 09:17 PM #32482 john curl   diyAudio Member     Join Date: Jul 2003 Location: berkeley ca V/nS? __________________ "Condemnation without Examination is Prejudice"
 10th January 2013, 09:25 PM #32483 DF96   diyAudio Member   Join Date: May 2007 Skin effect and proximity effect arise from Maxwell's equations and the 3-D version of Ohm's Law. These are linear. Therefore any solution must be linear.
jneutron
diyAudio Member

Join Date: Jan 2004
Location: away
Quote:
 Originally Posted by DF96 Skin effect and proximity effect arise from Maxwell's equations and the 3-D version of Ohm's Law. These are linear. Therefore any solution must be linear.
Review the equations. Find the absolute value "clause".

jn

simon7000
diyAudio Member

Join Date: Nov 2008
Location: Oakmont PA
Quote:
 Originally Posted by scott wurcer Excuse me, these numbers are at G = 1, the distortion making resistors must be imaginary. There is no current flowing in Rf in figure 4 save the (101x the error signal)/Rf. Come on guys, pay attention. Ed you mis-understood my joke, you said the thermal distortion was third order for a DRY resistor.
C'mon Scott, you know the drill. They are looking at the difference across a 10 ohm resistor with a gain of 100. The noise from just the resistor should be (back of envelope calc's) 100pV/Hz at the input. Add this to the 2.7 nV/Hz and you get 2.702 nV/Hz. (For those who have trouble with this addition please do a bit of homework before commenting.) With a gain of 100 that is 270.2 nV/Hz of noise. Now .00003% of 5 volts is 1.5 uV. So (1.5 uV/270.2 nV)^2 is a measurement bandwidth of 31 Hz.

Now they are measuring using an AP System 2, something I am familiar with. If I just go to the FFT analysis without stepping up the default resolution this level wouldn't even show up. Now at maximum rate the AP does go to -150ish re 1 V rms. But that takes 45 minutes or so. Without details on the settings of the AP one does not know if they were looking at noise or signal.

When they first did their setup they used higher value resistors. (So please don't give me they know what they are doing line... everyone makes missteaks.) I did tease BP about it and never got a reply, but the next time I looked they were using much lower value resistors.

ES

jneutron
diyAudio Member

Join Date: Jan 2004
Location: away
Quote:
 Originally Posted by john curl V/nS?
In Ed's test setup? No. I've delved in components and test setups using 400 V/nS with 8 amps per nanosecond, where the effects were right there in your face/slap you upside the head. But I've no access to an AP to try this at the low levels necessary in audio.

Let Ed do the test (if he wishes). It would be nice to confirm or refute a proximity based resistance modulation as applied to audio level signals and components.

jn

DF96
diyAudio Member

Join Date: May 2007
Quote:
 Originally Posted by jneutron Review the equations. Find the absolute value "clause".
?

scott wurcer
diyAudio Member

Join Date: Jan 2004
Location: dorchester ma
Quote:
 Originally Posted by simon7000 C'mon Scott, you know the drill. They are looking at the difference across a 10 ohm resistor with a gain of 100. The noise from just the resistor should be (back of envelope calc's) 100pV/Hz at the input. Add this to the 2.7 nV/Hz and you get 2.702 nV/Hz. (For those who have trouble with this addition please do a bit of homework before commenting.) With a gain of 100 that is 270.2 nV/Hz of noise. Now .00003% of 5 volts is 1.5 uV. So (1.5 uV/270.2 nV)^2 is a measurement bandwidth of 31 Hz. ES
What math? This circuit works as shown just fine a 65k FFT has about 1Hz noise BW and the distortion components are easily resolved. Ed the 1.5uV is also X101 to the output not just the noise. 1.5uV of thirds is 150uV at the output (that's the point of the circuit) the noise in a 1Hz BW is ~.27uV. I think Bob Pease included the pictures when he did it.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Last edited by scott wurcer; 10th January 2013 at 09:47 PM.

scott wurcer
diyAudio Member

Join Date: Jan 2004
Location: dorchester ma
Quote:
 Originally Posted by DF96 ?
Think one frequency in the Fourier domain the derivative has both signs, but it makes no physical sense to subtract AND add resistance by constriction of path. So I see seconds, sort of a rectifying mechanism.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

jneutron
diyAudio Member

Join Date: Jan 2004
Location: away
Quote:
 Originally Posted by DF96 ?
Examine figure 3 again. Pretend the conductor they show is actually cylindrical in shape. Pretend it is skinning as they depict, such that current is flowing on the surface. Then pretend that there is a return current right next to it such that the current on the cylinder is closest to the return conductor. In other words, substitute a cylinder for their rectangular section.

Now, is the picture of positive going current or negative going current?

The answer is, it is a depiction of current crowding INDEPENDENT of the direction in which the current is changing.

That is the "clause" I refer to.

The resistance of the cylindrical resistor can be modulated higher than the base resistance by the proximity effect. It CANNOT be modulated to be lower than the base resistance.

The resistance will modulate in only one direction. Given sine wave excitation and cosine slew, the resistance will modulate based on the absolute value of the cosine slew.

jn

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