@wyan001 - I’ll leave any comments on the USB cable to @grannyring since it his design and I have NO experience with this particular cable
The XLR design on my web site is from another DIYer in Europe and is a single/single design.
I am not sure if anyone has tried a Double/Double version - anyone built one?
I am not sure if anyone has tried the "Air" aaption either - anyone built one?
If I were to try building an XLR cable I would definitely go for the "Air" Adapton but opt to build a Double/Single version as follows:
For each of the +ve and -ve conductors I would use
- 2 x 18 or 20 gauge bare wires with each wire in their own Teflon tube
- twist the two wires "gently" together (one tiwst every 3-4 inches)
- NOTE: do not bother twisting the the two assembled conductors together - simply insert inside the Helix Coil
- For the Helix Coil I would used a 1 x 16 gauge Solid Neotech Solid UP-OCC wire with Teflon insulation
- but 2 x 16 gauge Solid Neotech Solid UP-OCC wire for the neutral Helix Coil could be used for a Double/Double design
- you could also try 2 x 18 gauge solid UP-OCC wire with Airlok Insulation from VH Audoi for the Helix Coil - the Airlok insulaton has a slightly better Dielectric Constant value
PLEASE NOTE - for the Air adapton the internal diameter of the teflon tube used only needs to be approximately 20%-25% wider than the diameter of the wire, which assures adequate air gap between the wire and the sides of the tube
If you do NOT want to use the Air adaption simply use insulated wire for the +ve and -ve conductors - For this I would use 2 x 18 gauge solid UP-OCC copper with Airlok insulatoin from VH Audio.
Hope that helps - Steve