John Curl's Blowtorch preamplifier

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#12,964
I once used a chopper stabilized servo and it is still working with Dave Wilson's Ultramaster analog tape recorder.
Because I used 450KHz bias on the record head, I had to reduce the inductance of the record head so that it would not self resonate at too low a frequency. This created coupling problems from the record amp and the record head, as the drive impedance at low frequencies is almost nothing. Normally I would use a non-polar cap of 30uf or more, BUT this would be too low a value for this situation. What to do? Well, why not servo the design with a chopper stabilized IC op amp? Remember, this is 1983, more than 25 years ago, and Scott Wurcer was just a kid. (joke). Really good op amps of the linear kind did not offer the offset that I needed. It worked, but this was a line drive application, not a preamp application. Please keep that in mind.
 
#12,965
SY said:
Lots of things are sold with no actual function other than in the mind of the user.

It's OK to not understand the mechanism of an effect, but when the explanation is hooey AND there's no data presented to show the existence of the effect, you'll have to pardon me for being somewhat cynical and believing that it's all a marketing exercise and an abuse of the patent system. It's analogous to a patent on a means of shielding against N-Rays. Now, if you actually have some real data, I'm all ears, so to speak. But I'd also wonder why it wasn't presented in the patent...

I guess I don't understand the analogy you draw to capacitor biasing (presumably, electrolytics), either from a dielectric physics or an equivalent circuit view.
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Biasing the dielectric of a cable is no different from biasing the dielectric of a capacitor.

There is no need to present data proving the functionality for a patent if the examiner accepts twhat you submit, and good reason for providing only the information necessary to get a patent. Background data is for the learned journals (unless you want to fund your lawyers next European vacation).

Its simple enough to try the biasing trick. Perhaps you should before you dismiss it. If it doesn't work for you that's fine. Most who have tried it seem to find it very beneficial. I have not made any money on either the patent or the "discovery". I would not recommend patenting anything if you are expecting to ever defend it.
 
#12,966
The book from 2007 by Vogel titled "Sound of silence: Lowest-noise RIAA Phono-amps - Designer's Guide " is also very good reading. It is about designing very low noise RIAA amplifiers using BJT, JFET, or transformer (or a mix of these).
Sound of Silence

Vogel uses MathCAD as a powerful tool in RIAA design.

I like to use a simulator aswell as MathCAD.




Sigurd

scott wurcer said:
Try Motchenbacher and Fitchen for a start. Unfortunately good stuff is spread pretty thin. you won't find a noise book with as much meat as, for instance, one of Donald Fink's books on TV.

http://www.amazon.co.uk/Low-noise-Electronic-Design-C-Motchenbacher/dp/0471619507
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#12,968
Using an AC mains powered computer and an USB EMU soundcard powered by the USB bus
connected to an old Technics SUA6 line amp,
I get this spectra.

Pavel,
you have a very clean spectra!
As you see I have some AC mains issues....




PMA said:
It can be well seen in the attached image - SNR over audio band is about 115dB (80.98 + 34.55 dB) (ref 1Vrms) :
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#12,969
Biasing the dielectric of a cable is no different from biasing the dielectric of a capacitor.
Click to expand...

Perhaps I'm not getting what you mean by "biasing the the dielectric of a capacitor." When I read that phrase, I think, "putting one end of a coupling cap, through which signal is passing, at a DC potential higher than the other." The measurable consequence for an electrolytic has been demonstrated and makes physical sense.

In the case of a cable or interconnect, the capacitance is a shunt, not a series. And the dielectric is polymer, not electrolytic, where biasing to low values of DC has not (to my knowledge) shown any measurable consequence nor has any controlled listening test supported the claim of more accurate signal transfer.

If I'm thinking about this the wrong way or there actually is data supporting the claims of more accurate audio signal transfer when the polymer dielectric of a shunt capacitance is biased to low-ish DC, I'd greatly appreciate being set straight.
 
#12,973
Yes, it is good, but still I do not like to have those main's components there.

I use FFT Size = 131 072, and Fs = 48kHz.
100 linear averages.
So, it is the same as yours.



Sigurd

PMA said:


Hi Sigurd,
your sound card has much lower background noise (would you mention sampling frequency and FFT memory, to get the RBW). My card ends somewhere at -135dB for 48kHz/128K FFT + 100x average.

So your result is very good.
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#12,979
SY said:


Perhaps I'm not getting what you mean by "biasing the the dielectric of a capacitor." When I read that phrase, I think, "putting one end of a coupling cap, through which signal is passing, at a DC potential higher than the other." The measurable consequence for an electrolytic has been demonstrated and makes physical sense.

In the case of a cable or interconnect, the capacitance is a shunt, not a series. And the dielectric is polymer, not electrolytic, where biasing to low values of DC has not (to my knowledge) shown any measurable consequence nor has any controlled listening test supported the claim of more accurate signal transfer.

If I'm thinking about this the wrong way or there actually is data supporting the claims of more accurate audio signal transfer when the polymer dielectric of a shunt capacitance is biased to low-ish DC, I'd greatly appreciate being set straight.
Click to expand...



With many dielectrics arguments about biasing will quickly lead to violation of symmetry. One step away from cable directionality
🙁 🙁 🙁
 
#12,980
Indeed.
I like the math for the RIAA transfer function and A-weighting
which I use in both MatchCAD and Microcap. Kinda interesting to see what the RIAA transfer function does to SNR for a ressitor vs SNR without the RIAA transfer function.

Still, the book could cover much more ground, which would fill another book😉



Sigurd

john curl said:
Vogel's book is pretty good.
Click to expand...
 
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