John Curl's Blowtorch preamplifier part II

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#81,081
simon7000 said:
I will be ordering some PC cards next week. Simple 2 layer FR4. So what test card should I use to measure how much the PC material really affects an audio signal? Should I lay out a winding long trace over a ground plane and drive it with a modest 10,000 ohm source and a high impedance 10 M load. Test this with square waves from say 20 -20,000 hertz?

Should I do an FET buffer with and without an input guard ring?
Click to expand...
Again, it is claimed that modern board materials do not have significant hook.
 
#81,082
@Simon7k
So you are looking for some measuring setup to discover differences in properties of different pcb material. Measuring with enough resolution you will find some in the end, but - you are not sure what you are looking for. And you do not know the criteria in real numbers for what is relevant for audio and what is not.
So, what is the point?:scratch1:
 
#81,084
bcarso said:
Levinson as well did stuff with a different dielectric, I think it was Arlon?
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From the owner's manual for the Nº32 Reference Preamplifier:

The Mark Levinson Nº38 introduced revolutionary volume precision
and resolution to the world of high end preamplifiers, with the firstever
0.1 dB-step volume control. In the Nº32, this same approach is
taken to an even higher level in a discrete attenuator of Madrigal’s design
that uses 66 surface-mounted, precision resistors per channel.
Used in combination, this balanced volume control gives us over
65,000 possible volume settings between zero- and maximum-attenuation.
(Don’t worry, we don’t use them all.)

This design, implemented on an Arlon 25N printed circuit board with
local, discrete regulators, delivers greater transparency than any volume
control technology we have ever experienced. It also provides increments
as small as 0.1 dB, allowing you to select precisely the correct
volume for any given recording, and to do so repeatably.
 
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#81,090
Just think about making capacitors out of circuit board material, and testing it against a more accurate capacitor in a differential subtraction test. In fact, if you took a dual metalized circuit board (a copper film on each side), you could easily make such a capacitor. Then test.
 
#81,097
Mike Gergen said:
Stupid question;
Has actual glass ever been used as a substrate?
Just curious.
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I bought some glass screen protectors as an easy way to build 2 layer construction smd T&M jigs using stick on copper foil as tracks and earth planes.
Drilling holes (diamond bit) would provide 'vias'.
It may be interesting to see how these sound as an audio pcb....these glass protectors are 3 layers...tempered glass, plastic layer and an adhesive so may not have the same ideal electrical characteristics as plain glass.

Here's an intersting way using microscope slides - youtube.com - How to make Clear Glass PCBs

Dan.
 
#81,099
Max Headroom said:
I bought some glass screen protectors as an easy way to build 2 layer construction smd T&M jigs using stick on copper foil as tracks and earth planes.
Drilling holes (diamond bit) would provide 'vias'.
It may be interesting to see how these sound as an audio pcb....these glass protectors are 3 layers...tempered glass, plastic layer and an adhesive so may not have the same ideal electrical characteristics as plain glass.

Here's an intersting way using microscope slides - youtube.com - How to make Clear Glass PCBs

Dan.
Click to expand...

Plating the barrels of the holes would be interesting...
Quite honestly though is there any point with the range of modern materials available today....
Better to use a high speed FR4 weave such as 7268 or even a high performance laminate...
https://www.altera.com/content/dam/altera-www/global/en_US/pdfs/literature/an/an528.pdf
why go to extremes with something that is totally impossible to manufacture a board reliably
 
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