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RE: UBYTE-2 Questions

Posted by Jon Risch (B) on March 27, 2012 at 21:33:55

In Reply to: UBYTE-2 Questions posted by Realitytunnel on March 27, 2012 at 15:15:45:

First, the UBYTE-2 recipe calls for a specific coaxial cable, one that has copper foil with a vestigial copper braid over the foil to make electrical contact at either end. The core surrounding the solid center wire of pure copper has hollow channels, creating a primarily air core dielectric, one with a very low amount of dielectric involvement.

The original production runs of this special coax (generally available only in Europe) had a decently thick copper foil, so when the copper braid is removed, there was copper all around the coax core, and it was thick enough to solder to, and to make good electrical connection.

Later production runs had the copper foil so thin, that it was being cut through by the copper braid, and was left in fragmented pieces that were electrically discontinuous and did not wrap around the whole circumference of the cable. Thus, the original coaxial cable used to make the UBYTE-2 is effectively no longer available.

YOU CAN NOT CONSTRUCT THE UBYTE-2 CABLE USING REGULAR ALUMINUM FOIL COAX.
Good electrical connection for audio frequencies can not be made to aluminized mylar, or even true aluminum foil.

If you try to build the UBYTE-2 with any other coax than the originally specified type, and a spool that has thick enough copper foil, IT WILL NOT ONLY SOUND TERRIBLE, BUT IT COULD FAIL AND/OR DAMAGE YOU AMP!

Some folks have taken various coaxial cables that had a foamed teflon core around a solid center wire, and removed the jacket and braid, and then laboriously wrapped copper foil from hobby shops (or copper tape from security supply companies) around the foamed teflon core, and created their own base cable for a UBYTE-2 construction. Needless to say, this is not only difficult, but the likely hood of the hobby grade or security grade copper foil being as pure as cable grade copper is virtually nil. You then also have to insulate the copper foil of each coax from the other, and this is not easy to do with quality materials.

All of this means that if you want to be able to build a cross-connected speaker cable, Belden 89259 is still the best bet, and while some folks seem convinnced that it is not the best way to approach this geometry, due to the stranded wires and strand based braided shield, it helps to keep in mind that the big bugaboo evil of stranded wires is supposed to come from skin effect, and we are talking about a relatively small center wire for Belden 89259 (22 ga.), and braid that only has a thickness when two braid weaves overlap of perhaps the equivalent of 32 ga. wire, and the fact that the coax braid is symmetrical about the cable center means the driving forces behind strand jumping are much lower than they are for wire of a gauge of 32 AWG.

Most of the signal passes through the cable braid, and a portion through the center wires.

So, as a result of these physical dimensions, and the electrical symmetry the coaxial cable possesses, the "evils" of stranded wires are not nearly as strong or pervasive as they would be for a zip cord construction, where you can really notice the problem with stranded wire when it is 12 and 14 gauge.

RE the reason for cross-connecting the center wire of one coax to the braid of the other, this creates a self-cancellation of the magnetic fields of the various conductors, which reduces the self-inductance of the overall speaker cable. As a result, the inductance of the cross-connected 89259 speaker cable is quite low, with out the usual penalty of having a very high capacitance as a counter-balance to the low inductance.

The only speaker cables with lower inductance tend to have capacitance's that are five to ten times that of the cross-connected 89259.

If you do not cross-connect the two coaxes, then the inductance is not that low, and the capacitance does not go down very much, leaving you with a much lower overall performance.
Jon Risch

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