Home Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

[ Follow Ups ] Thread: [ Display  All  Email ] [ Propeller Head Plaza ]
[ Alert Moderator ]

Re: Why is that?

[ In my own admittedly limited experience with say audio interconnects, I can't hear any difference between a $1 Radio Shack intrconnect inserted in the tape monitor circuit and shunting it out with the source monitor switch. ]

There ARE problesm with trying to use a tape monitor to test a cable, and I spell them out at:
http://www.AudioAsylum.com/forums/prophead/messages/3100.html

There are also problems with trying to use a "shunt" to test cables. The basis for this has been called the SWB test, or straight wire bypass test. However, there are several issues that come up once you start introducing additional switching contacts into the equation, as well as an arbitrary 'reference' chunk of metal.

Just as an example, this reference chunk of metal, the shunt, will it be shielded? If so, how, via an external metal box, a coaxial braid, foil, mumetal? ALL of these are different, and ALL will react differently to outside interferences, and present different impedances to the signal path.

Is there going to be a separate chunk of metal for the ground return? There almost has to be, because if you try to use the shielding enclosure as the ground return path, then your reference chunk of metal is no longer so simple and straight-forward, it now has a questionable ground return path.

Let's say we have two separate chunks of metal used as shunts, one is the "hot" shunt, and the other the "ground" shunt. Will your SWB test also lift the ground chunk/shunt to introduce the cable into the system? If it doesn't, then you have actually eliminated a portion of the cable circuit that is active in the real world when the cable is used with real components, as well as added additional circuit complexity to the cable circuit that is not present with a real world usage.

What about the purity of the reference chunk of metal shunt? Is it 6 nines copper? ETP copper, or even copper covered steel? Or is it silver, and then again, what purity level of silver?

Believe me, I am only touching on the surface of all the relevant questions and issues even a "simple" shunt could bring up.

When Peter Moncrieff of IAR fame was first getting into the use of the SWB to test unity gain components and cables, he found out early that the particulars of the bypass did indeed have an effect on what you perceived as "neutral", in other words, the shunt had it's own colorations, and so was tilting the test.

Now I don't agree with everything Peter has to say, nor do I embrace all of his methods either, but on this, I think he was on target. I say this because back when I was still learning about ABX, and was trying to make my own clone of the ABX switchbox, I found out how hard it is to get a really good switch that was truly neutral and sonically transparent (as well as finding out what the limitations of the ABX switchbox itself were).

If this is going to be done scientificaly, you can not assume that ANY portion of the measurement or test scenario is a "gimme", you can not take it for granted that all the other cables and switches and circuits are benign, and are not going to adversely influence the ability to measure/test/discern the DUT.


Jon Risch

This post is made possible by the generous support of people like you and our sponsors:
  Signature Sound   [ Signature Sound Lounge ]

Follow Ups Full Thread
Follow Ups
You can not post to an archived thread.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2025, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]