[GreenKeys] Incredible . . .

[Craig Sawyers]

> But some of those tube-audio guys are NUTs... I talked to one
> who claimed to hear the difference between carbon comp and
> metal film resistors. Okay! C U later! said I...

That is actually not so daft.  Look at the tempco of the resistors - carbon
comp resistors have several hundred ppm per degree tempco, and good
precision carbon film resistors about 10ppm per degree (down to around 3ppm
for precision items from Dale, Holco or Vishay).

If the resistor is disspating a little heat, low frequency (and often high
amplitude) signals modulate the resistance value in real time for carbon
composition, but nothing like as much for a precision carbon film (or metal
film, or bulk foil) resistor.

Now OK - the tube guys say that the carbon comp resistors are the ones that
sound better, and that is where my scientific approach breaks down.....

Incidentally, when I worked at Oxford Instruments here in the UK, we used to
use Allen Bradley carbon comp resistors as cryogenic temperature sensors
because the tempco was so high (and predictable).  When A-B ceased
production, we bought up tens of thousands of them to keep production
running for a decade or more.

Before Oxford Instruments, I was CTO of Wharfedale (a loudspeaker company).
To evaluate designs, we had a listening room with an acoustic curtain (so
you couldn't see what you were listening to) and used a double blind test.
The listener had a switch box, and could select only A, B, C etc - and
record his/her impressions on a test sheet.  It was really surprising what
sort of things had a strong correlation, and what didn't.  It seems that
most can clearly hear different loudspeaker cable and (I swear!) different
mains cable.  At the same time, in a multiple test where A and B were the
same loudspeaker design, listeners in general recorded them as having a
different sound.

To convince yourself one way or the other, make up a normal IEC lead, but
using house wiring cable - the sort that goes in the wall (in the UK we call
it twin-and-earth - solid wires for live and neutral, with a solid ground
wire between the two).  Easy to make up in 10 minutes.  Now replace one of
the normal moulded flexible cables on your hi-fi with the one you have just
made.

If you can hear no difference - fine.  If you can (and most people can) I
think you will be somewhat surprised.  And there is at least a plausibility
argument why.

Craig