Is it worthwhile to buy Bulk Metal Resistors?

[Conrad Hoffman]

Nonsense. I keep manganin wire on hand and often make my own custom low value shunts and non-inductively wound resistors. Still, even a non-inductively wound resistor won't have the HF performance of the bulk metal devices. Fortunately I can't hear the difference between resistor types, and suspect that if any difference exists, it has more to do with strays and tolerance, than the resistance material itself.

[abzug]

Originally posted by Conrad Hoffman
non-inductively wound resistors.

How does one wind to get it non-inductive?

[abzug]

Also, I'd like to ask whether the S102 (around $12 at Percy Audio) are really that much better than the VT-55/54/52 (around $7 at Partsconnexion). They're both bulk metal foil.

[Bobken]

Originally posted by abzug

How does one wind to get it non-inductive?

Originally posted by abzug
Also, I'd like to ask whether the S102 (around $12 at Percy Audio) are really that much better than the VT-55/54/52 (around $7 at Partsconnexion). They're both bulk metal foil.

Hi,

Look up "Ayrton Perry" for non-inductive (or low-inductive) resistive winding info.

Having carried out a lot of resistor 'listening' trials, I didn't find the larger circular-bodied Vishay Bulk-Foils to be quite so good sonically as their other varieties like S102, VSRJ etc., which are in a less-substantial flat package.

As the best for me sonically are the so-called Naked Vishays, which are TX2352 from Texas Components, I can only guess that these very small sonic differences are related to the amount of epoxy packaging used, as the Naked Vishays don't have any such encapsulation at all. Otherwise, according to the makers, the resistive elements used in these Vishays are the same.

Regards,

[abzug]

Do the 'naked' Vishays have resistive elements actually exposed to the air?

[Bobken]

No,

They have what looks to be a clear, possibly epoxy or similar type of varnish coating the entire device.

There is no added mass as with any usual plastic-encapsulated resistor like this, though, and this is the only apparent significant difference which I am guessing gives rise to the slightly-improved sonics.

Regards,

[Conrad Hoffman]

There are various ways to wind non-inductive resistors, some better than others. None of them will give the performance of a bulk metal foil resistor, though you have a greater choice of materials, if you believe materials affect the sound. IMO, that remains an interesting area of research.

The easiest way is to take the required length of resistance wire and fold it over in the middle- a bight, I believe. Fasten the fold to the form, keep the two leads close together, and wind. A flat form (mica was the old method, and I still use it sometimes) is good because it keeps the loop are small, thus the inductance small. The parallel wire also cancels out the inductance. Resistors wound this way are very good out to a few MHz.

You can also twist the wires a bit to keep them close. This helps the inductance, but increases the parallel capacitance even further, and probably increases the risk of insulation failure. It also looks bad, so I don't do it that way.

Another trick can be learned from the big ten turn pots. If you take one apart, you'll find the resistance wire has been wound on a piece of heavy copper wire. That is then wound around the body of the pot for the wiper to ride on. The coils are small, so the inductance is small, plus the copper wire reduces the inductance still further. This method is good to several hundred kHz or more. Interesting side track- look up tuning wands with brass and iron ends, and how they work.

Remember that these parts can be physically large, so stray capacitance to the chassis and other parts of the circuit has to be considered. IMO, that's a big factor with Teflon and polypropylene high end audio caps as well.

[FoilEngineer]

Hi all,

I just wanted to let you know that Vishay is now going to release Z-Foil "naked chip resistors"
We're on the final stages of testing and the datasheet is just about ready.
It should be fully published and available within about 2 weeks.

If you have any general questions about the Vishay Bulk Metal Foil, feel free to ask.

[Bobken]

Hi,

Now that is some interesting good news.

Having used the VSRJ, VSH and S102 series for very many years, and nothing else comes to close to them 'sonically' in my experience, I was pleased to try some TX2352s in a more-recent commercial design, and these were slightly better still than the encapsulated versions.

In fact I commented on this in the "Blowtorch preamplifier" thread only yesterday.

Thanks for letting us know.

Regards,