John Curl's Blowtorch preamplifier part II

[wayne]

Originally Posted by scott wurcer

And then they will love the -36dB one above all.

Of course they will it has no feedback resistor!

[jcx]

Originally Posted by simon7000

Others measure better on third order distortion. Low tempco is nice low and linear is better.

any references that show that?

Vishay Z-foil claims "< 0.1ppm/V"

so -140 dB would at worst require 1 R/V of output

Bruce Hofer of AP Analog Design presentation seems pretty clear on Bulk Metal Foil having lowest V coefficient - admits most other technology R don't spec it but he is certainly in a position to have measured lots of devices to very high resolution

[simon7000]

Originally Posted by jcx

any references that show that?

Vishay Z-foil claims "< 0.1ppm/V"

so -140 dB would at worst require 1 R/V of output

Bruce Hofer of AP Analog Design presentation seems pretty clear on Bulk Metal Foil having lowest V coefficient - admits most other technology R don't spec it but he is certainly in a position to have measured lots of devices to very high resolution

We were not talking about Voltage coefficient. We were talking about tempco.

The tempco can be 10 ppm/C but if that is limited to 0-100C and is actually of the K*Xexp2 with a limit of 10ppm at 100c then that will have more odd order distortion a than 10ppm tempco that is is 10 ppm at 0C and 100C.

Then there is the issue of thermo electric effects.

But look at the Linear Audio article which shows the distortion of bulk metal and other types.

[jcx]

hard for me to tell what you're talking about much of the time

or where you get your numbers:

“Z” foil presents a tenfold improvement in the TCR of Bulk Metal® foil
resistors, typically ± 0.2 ppm/ºC from -55ºC to 125ºC. Maximum TCR is
±0.2 ±0.6, ppm/ºC from -55ºC to 125ºC, for resistance values ≥100
ohms. From 0ºC to 60ºC the typical TCR is ±0.05 ppm/ºC. “Z” foil is the
closest thing yet to zero TCR in a resistor.

60 C seems a OK amp internal temp target, 10 mW is 1.5 C in a 150 C/W R

1.5 C * ±0.05 ppm/ºC is ±0.075 ppm - seems like we can typically manage better than -140 dB from TC if we care to spend for the R, vent the case



thermocouple emf follows the delta_T between junction of differing metals

by soldering both ends of the R into Cu PCB trace of similar weight we have somewhat reduced the differential delta_T

Thermal EMF: 0.05 μV/°C

I don't know the exact test conditions - probably documented on Vishay site

but lets just go with the 1.5 C delta, to get: 75 nVpk

so EMF is estimated as a series 75 nVpk following the power envelope curve, themal excursion heavily filtered at audio by the thermal time constants of the R

once again not quite reaching -140 dB in a 1 V signal

[morinix]

What is this thread about now?

[bcarso]

Originally Posted by morinix

What is this thread about now?

Potential distortions due to passive components, (somewhat distantly) related to what components account for sonics of JC's preamp.

[jcx]

good question, Simon seems to be digging deep under the noise floor to "explain" why amps driving dynamic loudspeakers with dB of power compression sound different

the example is single digit, at worst low 10s of C delta_T in properly selected feedback R with few ppm /C TC

vs sometimes over 100 C delta_T in voice coils with >30000 ppm /C

http://www.klippel.de/uploads/media/...ransfer_03.pdf

apparently Golden Ears can "listen through" these loudspeaker distortions of thousands times greater magnitude, even sharing fundamental cause, presumably similar "audio character" to "know" you've changed from "old" Holco to "unapproved" TX2575

[simon7000]

This is the distortion of a naked Vishay bulk metal film resistor test. An individual resistor would have 6 db more distortion.

Argue with yourself all you want. But it would be more productive if you looked at the material even the stuff on resistor distortion in this thread.

[morinix]

Originally Posted by bcarso

Potential distortions due to passive components, (somewhat distantly) related to what components account for sonics of JC's preamp.

Somewhat?!

[bcarso]

Originally Posted by morinix

Somewhat?!

I am trying of course to be diplomatic. However, after exhausting the basic topic in part I and part II, and continuing to reassure people who merely want to copy JC's design that he will not provide any further details, things have run fairly far afield --- although I still think, touching on areas of interest in general.

In this latest diversion one of the things lacking is disclosure of the test instrumentation details.


Brad Wood