KLE Innovations Classic Harmony Plug - Bullet Plugs
KLE Innovations Classic Harmony Plug - Set of 2 - Bullet Plugs

HiFi Accessories · Connectors & Plugs

The RCA plug has remained virtually unchanged for over six decades — a connector designed by the Radio Corporation of America that became a global standard more through inertia than merit. Keith Louis Eichmann, an Australian engineer with an obsession for electron flow and signal purity, challenged this status quo back in the late 1990s with his legendary Eichmann Bullet Plug. The philosophy was as simple as it was radical: less mass, better geometry, purer materials. After founding KLE Innovations (KLEI) in 2013, he took that concept further with the Harmony Plug — a wholesale rethinking of the phono connector. The Classic Harmony is the entry point to this line, and it is far more than a budget compromise.

What appears at first glance to be a modest RCA plug is the result of rigorous mathematical modelling: pin mass, cross-section and alloy composition are all tuned for optimum electron flow — not for ease of manufacture or maximum margin. The proprietary copper alloy achieves conductivity values exceeding 101% IACS (International Annealed Copper Standard), the global benchmark for electrical conductivity. For reference, the gold-plated brass contacts found in the vast majority of off-the-shelf RCA plugs achieve just 28% IACS. This physical reality is audible — and it is why the Classic Harmony has been regarded as a benchmark in its price class within the DIY HiFi community for years.

The Eichmann Bullet Plug, developed by Keith Louis during his time at ETI in Australia, was far ahead of its time: while every other manufacturer relied on solid round contacts, he reduced mass radically and isolated signal from ground with precision. The audio press responded with enthusiasm. When KL left ETI in 2013 and founded KLEI, he faced the challenge of not just continuing the concept but rethinking it from the ground up.

The result is the Harmony line: signal and ground pins are no longer round but flat and tag-shaped — which makes soldering significantly easier, even with thin solid-core conductors or complex multi-layer screened cables. Between the two solder tags sits an anti-short shield, a valuable safeguard particularly for less experienced builders. Signal and ground pins are also arranged at maximum distance from one another to minimise capacitive coupling — a detail that is measurable in the laboratory and perceptible in listening.

The heart of the Classic Harmony is its proprietary copper alloy. KLEI deliberately avoids tellurium copper (92–95% IACS), widely used in audiophile connectors as a compromise between conductivity and machinability, and brass, which at 28% IACS functions almost as an insulator by comparison. The specially developed alloy achieves extrapolated conductivity values of over 101% IACS — a figure that seems paradoxical at first glance, but is physically explained by the crystallographic purity and specific microstructure of the alloy. A high-purity silver plating protects the surface from oxidation and ensures long-term stable contact properties.

The housing is made from a high-temperature thermoplastic with an extremely high melting point — a conscious break from industry norms where cheaper polymers routinely yield under soldering temperatures. Anyone working with silver solder or high-temperature irons will notice the difference immediately: no warping, no melting, no compromise at the bench. Cable retention uses two screws that firmly secure the cable sheath — compatible with outer diameters from 4 to 9.5 mm (with detachable rubber grommet from 3.5 mm). The plug head itself uses a snap mechanism: it seats precisely in the RCA socket with no play, yet releases easily without tools. The ground pin also features thread teeth that provide defined star-point grounding when used with a conductive metal or carbon fibre housing.

The Classic Harmony is designed as a DIY connector and can be assembled without difficulty even by beginners. The tag-shaped pins offer ample soldering surface for both solid-core and stranded cables. KLE Innovations recommends a burn-in period of at least 125 hours before forming a final sonic judgement — a recommendation taken seriously in the community and related to the crystallisation of metal and solder joint under signal flow. Those who allow the connector to settle before evaluating will be rewarded with a substantially more resolved and coherent result.

Ideal cable partners include high-purity copper or silver-copper hybrid designs — such as Duelund Copper in Silk or cables from the Jupiter range — since the Classic Harmony passes the quality of the conductor to the system without addition or subtraction. It neither colours nor veils: a quality that only fully reveals itself when the cable itself follows the same philosophy of transparency.

The Classic Harmony is the entry point into a product family designed to scale upward with purpose. Above it sit the Copper Harmony (copper-silver alloy, also >101% IACS, silver-plated), the Silver Harmony (pure silver ground pin), the Pure Harmony, and then the Pure22, Perfect22 and finally the Absolute Harmony as the flagship. Each step builds on the same underlying philosophy while refining material purity, geometry and execution further. Those who start with the Classic Harmony are already thinking in the right category — and will quickly understand why KLEI has earned a devoted following worldwide.