John Curl's Blowtorch preamplifier part II

[john curl]

We understand, Pavel, and I agree that this is important. Thermal capacitance is the key, and, of course, tempco. This is one of the reasons why I specified Holco resistors as feedback resistors, approximately 20 years ago, in the Parasound HCA2200. Thicker leads and larger body than even 1/2W Resistas.

[1audio]

Building a reference divider for surge testing is very challenging. Construction to balance the voltages at high frequencies uses lots of tricks to compensate for errors. Here are some examples of hv versions: High Voltage Divider Making a small one using similar techniques would make sense. The challenge is verifying its performance.

[john curl]

What I am hoping for and getting, is results that show differences. It is all nice to be as accurate as possible, but nit picking about what COULD go wrong, or what makes a PERFECT test, doesn't show results, just the headaches.
For example, once, Dr. Hawksford 'nit picked' Walt Jung, Scott Wurcer and me, because the EQUATIONS showed that a real capacitor's inductance would effect the NULL. What he overlooked is the the AMOUNT of deviation could easily be controlled by proper choice of the test signal settings, and by bandwidth limiting the test signal with a quality polystyrene cap to have just enough rise-time for the signal to show properly on the oscilloscope screen. This removed the problem that SEEMED so apparent in the equations. Had Dr. Hawskford contacted me in advance, or tried the test, himself, this would have become self evident. However, please remember that Dr. Hawksford and I are competitors, as well as colleagues, and a 'justifiable criticism' by him, might make him look like he was really on top of it. Matti Otala did the same thing to me, on occasion, as well. Seems to be a PhD trait. ;-)

[megasat16]

I've been following this thread for so long and I currently have no mean of testing a resistor noise down to -170dB considering the equipments I owned are very old and not calibrated to make such accurate tests.

But I am wondering what's noise is more important to look at. i.e those coming from switching of active devices such as transistors or the noise (thermal/ white/pink/eletctro-magnetic induced noise due to the conduction of electricity in the metal) of passive devices such as resistors?

I understand the concept of everything else matters in a good circuit but the practicality of obtaining such low noise resistors that needs to be matched and pre-selected for a DIY community or mass production seems to be of much difficulty.

[iko]

Originally Posted by john curl

However, please remember that Dr. Hawksford and I are competitors, as well as colleagues, and a 'justifiable criticism' by him, might make him look like he was really on top of it. Matti Otala did the same thing to me, on occasion, as well. Seems to be a PhD trait. ;-)

Have you never done this?

[john curl]

Sure.

[iko]

I don't think there's a man who hasn't or will not do it. It's a human trait.

[john curl]

Simon, you may have mentioned it once, but what resistors are you using for the REFERENCE resistors in the bridge?

[Professor smith]

However, please remember that Dr. Hawksford and I are competitors

In what sense are you competitors? can you explain?

[john curl]

We both design audio products, as consultants, for money.