a/b interconnect cable comparison single ended

John's idea of using the tape look to simply route signal through the cable is a good one, but there is one catch. That is, if you've not used the tape loops to any great extent, just switching them into the circuit will change the sonics regardless of the cables under test. This obviously has to do with "break in" and many will think that it is kinda crazy, but it is true. If in doubt, plug your CD player into a different input that you don't normally use ( NOT a phono input ) and see if you can hear a difference. We've done this using even mass produced receivers and the differences between various inputs was quite evident, even to the "non-audiophiles" that first noticed the differences in their system. Sean
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Jea48: Using the tape loop allows one to use their existing set-up and simply switch the interconnects in and out of the system instantaneously. No need to remove, replace, reconnect, etc... All of this at a flip of a switch WITHOUT altering the load impedances by running cabling in parallel to two different input jacks. Sean
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"I know the tape loop method will allow easy switching back and forth, but is it a true A/B comparison?"

This is a method to see how "coloured" a cable is. It may not be representative of how the cable actually works in a different part of the circuit with different mating impedances.

"Is the signal path and switching contacts of the tape loop cicuit the same as the line inputs signal path and switching contacts of the preamp?"

This would depend on if the output jacks on the source were wired in parallel or if they were individually selectable. If they are in parallel, it would not be the same. If they are selectable, it would be almost the same. The difference would be that you would have to select outputs on the source and the inputs on the preamp. This would mean introducing two switches and their associated parts / signal path into the circuit rather than just one. More variables with more potential for outside influences.

On top of that, signal goes wherever it can, even if the circuit is open and there isn't a complete path for it to take. This is especially true of RF based signals, such as the digital output on a transport that one might use to feed a DAC. I know that this is contrary to what many people have been taught, but there's nothing that i can do about that. Since the cables themselves present a nominal impedance, signal will flow and they will effectively become part of the "load" that the device sees. This is true even if you and i see it as an "open circuit".

As such, using a device with parallel outputs and choosing between the cables at the preamp still places the nominal impedance of the unused interconnects in parallel with the signal path of the interconnects being used. Nothing short of switching them out of the circuit at the source or physically removing them would solve this potential variable.

"And are you not putting the two ics in series with one another when using the tape loop".

My take on this was that the system remained as it was and one was simply inserting cables for testing into the tape loop. This would allow one to maintain the sonics that they were used to and at the same time, allow them to switch the interconnect in and out as desired via the tape loop. If one noticed a large difference, the cable itself would probably be introducing its' own sonic influence. As previously mentioned though, there would also be additional impedance related alterations to the signal path due to the tape monitor circuitry and additional switching, etc...

As to your specific installation, i'm not directly familiar with either piece of gear i.e. the Arcam or the SF preamp. How each piece works in terms of selectable inputs and outputs and loading characteristics is a mystery to me. Sean
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That's what i thought you meant Jim, but thanks for clarifying it. That would put the cables in series, but as we've discussed, it would be far faster and more convenient to do this than to have to manually connect / disconnect as needed when trying to make this type of comparison. Sean
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I discussed hooking cabling up to a distortion analyzer quite a while back. Some cables are far higher in distortion than others. John Curl has also discussed this over at AA.

With that in mind, this type of test still doesn't simulate the way that a cable acts as an impedance transformer between pieces of gear. Since no two pieces of gear have the same input / output impedances, the loading characteristics, distortion and sound WILL change somewhat from system to system / component to component.

As far as the approach that David Salz recommended, it really can't tell you too much of anything. One could easily see the electrical differences between the two cables and the variances in signal flow when hooked up in series using a network analyzer. However, attributing what sonics go with what cable, regardless of where Cable A is in relation to Cable B or vice-versa, would be nothing more than a crapshoot. That's because the source sees the combined electrical characteristics of the two cables and load component on the whole. Thevenin's theory teaches that the sum of impedances can be summed into one impedance. Then again, i've never been a huge fan of Thevenin's theory. Lumped and distributed impedances can and do very different things electrically, even though they might sum into equal values if looking at the circuit on the whole. Sean
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Altering the source and load impedances can vary the response that a cable would demonstrate under these test conditions. This is the same thing that happens when you change components i.e. the load and / or the source impedance is altered. As such, one can simulate various circuit combo's and see how each cable responds accordingly. Why there aren't any reviewers / manufacturers doing anything like this, i don't know. Sean
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