About Vishay resistors
Resistors built using Vishay's bulk metal foil technology have shown themselves in my blind listening tests to be consistently more neutral and transparent than all other small-signal resistors, but they are very expensive. Many companies boast that they use Vishay resistors, but unless they are using bulk-foil resistors made from Vishay's C, K, or Z foils, they're using ordinary penny resistors from companies which have been purchased by Vishay. In other words, they are buying cheap resistors and selling you BS.
Here's why a company can use cheap resistors and claim to be using the good ones: Vishay is a huge company which has purchased dozens and dozens of other companies, such as Dale, Sprague, etc. ( the full list is here) - they will purchase any and all companies which compete with them.
Resistors from any of those subsidiary companies can be correctly called "Vishay" resistors, since they are owned by Vishay, but one company, Texas Components Corporation --TXCC-- is franchised by Vishay to complete the manufacturing process on resistors using Vishay bulk metal foil resistive elements purchased from Holon, Israel. TXCC is the largest manufacture of Vishay foil products in the western hemisphere, and are the company which makes the bulk- foil resistors that made the Vishay brand famous in audio circles.
Their S102C/K is the original bulk-foil resistor (you can buy these resistors from Michael Percy Audio). It's a very fine sounding part, and gets even better with the encapsulation (the plastic "box") removed and only a thin film of conformal coating on the foil to protect it. In its "naked" form it is called the TX2352: the renowned "naked" Vishay resistor .
Better even than the TX2352 is the Z201 bulk foil resistor, also made by TXCC. It uses the top-secret Z foil provided by Vishay, Israel. Resistors made Z foil cost four times more than the naked C/K foil TX2352 resistors, but they are more than 10 times better (electrically). Z foil resistors are intended for applications requiring extraordinarily low temperature coefficient, a common requirement in measuring instrumentation. More important to us audio guys is the fact that they sound fantastic.
While the TX2352 is sonically head and shoulders above all the other ordinary resistors, the Z201 is substantially -- not marginally -- better than that. They are more coherent, more natural, completely uncolored, fast, dynamic, nearly neutral, and nearly as close to a 1-12'' piece of wire as I've ever heard a resistor be, possessing only the tiniest trace of "resistoritis" -- a nearly imperceptible thinning of the sound, an impressive achievement.
And it doesn't stop here: TXCC has announced a new "naked" version of the Z201: the TX2575. Is this resistor perfect? No, no resistor is perfect. But it's as close to audio nirvana (in terms of absolute neutrality when compared with a bit of wire) as any resistor has ever come. At this time of writing (Feb, 2008) it doesn't get any better.
Here then, is the hierarchy of small-resistors,* from great to mediocre:
TX2575: the "naked" Z foil resistor
Z201: the original Z foil resistors,
TX2352: the original "naked Vishay"
S102 C/K: the encapsulated C/K foil resistors
"Vishay" resistors: any and all resistors built by a company owned by Vishay. Some good, some bad, most inexpensive, none great-sounding.
* As opposed to power resistors. There are no bulk foil power resistors that I am aware of. For power resistors I've found the best so far to be Mills audio-grade noninductive resistors.