Top resistors

05-26-13: Rodman99999
Testing capacitors for outer foil, has shown me how much influence a body can have regarding induced noise.

Exactly! And my suspicion is that if he were not holding the resistor in his fingers, he would not have had enough signal to make a meaningful measurement.

Note this statement in the page he links to about the corresponding measurement for capacitors (for which his methodology seems to me to make more sense):

How to do the test with Oscilloscope? Simple by testing both leads, and give some “interference” outside the capacitor (touch by hand or put some electric field interference e.g. high voltage cable, etc). The side with higher noise, means the outer foil.

Regarding

Why would the impedences of the probes, ground wire, etc not remain constant?

They would remain constant, of course, but the impedance of the path between his fingers and the probe's ground would depend on where he was grasping the resistor, and on which end of the resistor the ground clip was connected to. Likewise for the impedance of the path between his fingers and the probe's tip.

Visualize the situation taken to its extreme: He grasps the resistor at one end (without touching the lead). Regardless of the resistor's directionality or lack thereof, it would certainly seem expectable that he would see something different on the scope depending on whether the probe's ground or tip were connected to that end.

If the results were repeatable, and mostly constant, between resistors of the same value; I'd see no reason to doubt the conclusions he's made.

If the measurement were repeated for a number of resistors of the same type and value, and if he grasped each of them at approximately the same position, and if he kept his body located and positioned similarly throughout all of the measurements, I'd expect the results to be reasonably consistent. However, I don't see how those results would say anything about the directional characteristics of the resistor. They would just say something about the net result of the interplay of the five factors I listed in my previous post.

Regarding my previous post, btw, upon re-reading it I realized that the following sentence is flawed. Consider it to be deleted from the post:

That conclusion would be true even if he managed to grasp the resistor exactly at its mid-point, due to the differences in AC leakage to the probe's ground and its tip.

Regards,
-- Al

Bruce Hofer (founder of Audio Precision) did a recent AES Convention lecture on many topics pertaining to low-THD circuit design, including parts quality in both capacitors and resistors. He was kind enough make the PowerPoint slides available for download in his May newsletter, which can be found here: http://www.ap.com/kb/list/2

You do have to register to have access, but there's a wealth of tips available from one of the true modern masters of analog audio design.

As an update, I installed the naked Vishays and overall found them to be better in my preamp that the other resistors I used. Not a warm sounding resistor but open, detailed and good tone without any edge. Very good clarity. Lucky for me I can change them on the fly anytime I want. As already mentioned, mine are in a preamp and not tested in an amp or speakers, etc. I only require two resistors, one for each channel.

If you want a little warmth added to that transparency you could add a Riken Ohm in series, following the Vishay. Of course you would have to use different values to sum to the value you want.

I did something similar in my Hagerman step up. There are 2 resistors in the signal path. The first one I use the naked Vishay, but using that in both spots was just too revealing. Adding the Riken Ohm carbon to the second spot was (as the baby bear says) just right. I then used the leftover Vishay for cartridge loading, with another improvement.

Can Anyone help me identify the wattage of Caddock MDN0178 11.75ohm, 2% resistors used in the tweeter section of Wilson Audio Sophia 3?
I'd like to change it for an 8ohm resistor but don't know the required power capacity.