John Curl's Blowtorch preamplifier part II

[marce]

What would you class as a world class product:
daresbury particle accelerator, a mass spectrometer,an electron microscope, vehicle intercom system, a radar system, flight control systems, MRI scanner, M777, Nikon D4 etc etc

[flg]

Originally Posted by marce

What would you class as a world class product:
daresbury particle accelerator, a mass spectrometer,an electron microscope, vehicle intercom system, a radar system, flight control systems, MRI scanner, M777, Nikon D4 etc etc

Certainly not a "vehicle intercom system" which was the only audio product you suggested that we might even be concerned with in this thread? What's your point? Or, are you the devils advocate and you don't need to focus on this thread's topic?

[rsavas]

I find it hard to understand why epoxy/glass dielectric composition in a PCB, can not be used for 100% of all audio designs!! It is even used for many high power applications, which have metal cores, for say LED mounting applications. I believe that the Tg of epoxy/glass construction approaches or exceeds the maximum junction temperatures of silicon devices. So, is the reason, to not use epoxy/glass construction, is of a signal propagation issue (we are talking audio frequencies here!!) or a thermal issue or both?
Everything does in a sense require justification or it just does not make any logical sense, IMHO

Regards
Rick

[bcarso]

Originally Posted by elektroj

Here's the nice tutorial:
Tom Jerse and Mark Terrien, "A Designer's Guide To Shielding"
http://www.hparchive.com/seminar_notes/a-104.pdf
Apologies if it has been posted here before.

That is spectacularly good! Oh the good old days at HP (in some ways at least, that continue at Agilent).

[SY]

Originally Posted by rsavas

I find it hard to understand why epoxy/glass dielectric composition in a PCB, can not be used for 100% of all audio designs!!

Marketing. It's better, apparently, to use a floppy material with high triboelectric properties from which traces readily delaminate because it's more exotic/expensive and somebody wrote an article in a popular audio magazine 40 years ago showing that it was better in a totally unrelated application.

The exception (and even that can be dealt with) is ultra-high impedance applications, i.e., condenser mikes.

These exotic materials can be useful for many things, but audio isn't one, absent fashion and image.

[cliffforrest]

+1 @bcarso #28084

I have never seen it all so concisely compiled. Not that I understand the half of it, but am studying ....

Yes, HP and Tek documentation was an inspiration during my formative engineering years!

[rsavas]

Now we are getting to the technical points in justification = "Marketing hype" of not using epoxy/glass construction :-) As my Dad, once taught me, "BS baffles brains"

Cheers
Rick

[Wavebourn]

Originally Posted by SY

The exception (and even that can be dealt with) is ultra-high impedance applications, i.e., condenser mikes.

In condenser mike I prefer to drill a bigger hole in PCB, and put through it a leg of 1 GB resistor with short Teflon tube on it.

I is a single point where coupling capacitor, FET gate (or tube grid), and grid leak resistor met. Well, there may be one more where met each other a wire from capsule, a resistor that supplies polarizing voltage for the capsule, a wire from the capsule, and still the same coupling cap. The same hole in PCB and the same short small Teflon tube is sufficient again. Why should I bother with Teflon PCB if it does not provide any advantages?

[SY]

That's one good way. Guard rings work, too. I use Teflon turret standoffs.

[john curl]

Last night I saw a documentary on the Alma telescope project. There, I found WORLD CLASS fabrication and I felt a 'kinship' with the manufacturers of the telescope. It makes my colleagues and my efforts look stingy and compromised by comparison, but at least, we are trying our best, within our budgets.