Connectors for Audio – The problem of Self-Inductance with thick metal parts.
From “The Complete Guide to High-End Audio”… Page 290. “We want a large surface contact between the cable’s plug and the component’s jack, and high contact pressure between them.”
From Matthew Bond: Actually, the best we can strive for in terms of audio connections and electrical transfer, is high contact pressure (gas-tight) with a small amount of surface area in ‘intimate contact’. The trade-off with a larger surface area is that contact pressure is reduced and contact is inconsistent. Instead, high contact pressure over a relatively smaller area is the desired reality. The best example of this is the ETI Link RCA connector. The RCA plug and RCA jack rely solely on high contact pressure with minor surface area contact.
The worst connector for audio is any large, thick, or massive design because of increased self-inductance. A classic example of the false logic in audio connector design is the traditional 5 way binding post. The larger and thicker these connectors get the worse the sound becomes due to increasing self-inductance and high-frequency attenuation. In a few words: loss of detail, high frequency extension and upper octave air.
The best connector for audio frequencies is a thin-walled copper tube, seen in some banana plugs. As yet there is no mating connector with the same design and engineering concept at the amplifier or loudspeaker end.
The traditional style banana plug is about 14 AWG or 2.5mm in diameter or thickness, and also attenuates high frequencies, making it sound dull compared to a spade lug.
A normal spade lug owes its superior sound due its reduced thickness or profile compared to the traditional banana plug. The typical thickness of a spade lug is around 18 to 16 AWG or 1.2 to 1.5mm.
A common misconception about spade lugs is that the flat surface areas of a spade lug are in consistent contact within a binding post, and that there is greater ‘surface area’ in intimate contact. This is not true. The spade lug sounds better because it usually has a thinner plate or wall thickness (less self-inductance) and has better high frequency extension.
Consider this; the four separate mating surfaces of a spade lug in a binding post have unmatched, inconsistent and unreliable ‘plate to plate’ contact of their separate ‘surface areas’.
The reality of the connection of a spade lug is this; when the spade lug is inserted into the binding post, the rotating top section of the binding post creates small circular cuts into the upper surface of the spade lug, and this is in fact, the primary electrical contact between the spade and the binding post.
Try this with a few fresh, new, shiny, gold-plated spade lugs… install and check visually, and then you’ll be able to see that the primary contact is mostly a small number of lines.
I would concede that with greater torque and under greater pressure, the four separate mating surfaces of a spade lug in a binding post would have improved contact of their separate surface areas. But there is no such binding post that can mechanically torque down to the kind of ‘plate to plate’ surface area contact that we wishfully imagine is happening in the spade lug and binding post interface. In any case, the perfect binding post would need higher conductive materials with less mass, less structure and therefore less mechanical strength, and would fail to provide high contact pressure.
From “The Complete Guide to High-End Audio”… Page 291. “Most high-quality RCA plugs are copper with some brass mixed in to add rigidity.”
From Matthew Bond: The RCA plugs used by most high-end audio cable companies, are actually made from Free-Cutting Brass, Copper Alloy No. C36000 (Alloy 360). Alloy 360 is a standard alloy of copper (60%) and zinc (40%) with a small percentage of lead to ensure the ‘free-running’ or ‘free-cutting’ in machining operations. I have tested the cross-section of many of these RCA plugs by simply filing away the plated surfaces. A fine round file, reveals the plating materials and usually at less than 20 microns, bright yellow brass appears.