I love interesting weird audio problems—the stranger the better! When a colleague reached out with a baffling issue of severe signal loading on their freshly built instrument cables, I knew it was right up my alley. It involved high-quality components behaving badly, and it was a great reminder that even experts can overlook a small but critical detail buried in the cable specifications.
The Mystery of the Missing Signal
My colleague was building cables using Mogami instrument cable (specifically 2319 and 2524) and Neutrik NP2X plugs, both industry-standard choices. The results were perplexing:
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With Neutrik NP2X plugs: The signal was heavily compromised—a clear sign of signal loading—requiring a massive 15dB boost just to achieve a usable volume.
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With generic ‘Switchcraft-style’ plugs: The cables functioned perfectly, with no signal loss.
The contradiction was the core of the mystery: Why would a premium connector fail where a generic one succeeded, all while using the same high-quality cable?
The Sub-Shield Suspect: A Deep Dive into Cable Design
The answer lay in the specialized design of the Mogami cable, particularly a feature intended to prevent noise. Most musical instrument pickups, like those in electric guitars, are high-impedance, voltage-driven circuits. This makes them highly susceptible to microphonic noise—the minute voltage generated when a cable is flexed or stepped on.
To combat this, the Mogami W2319 cable specification includes a specialized layer:
| Layer | Material | Details |
| Sub-Shield | Conductive PVC (Carbon PVC) | Placed under the main shield to drain away this microphonic voltage. |
This sub-shield is designed to be conductive.
The Termination Trap
My colleague’s standard, logical termination procedure was to strip the outer jacket and shield, then solder the hot wire to the tip connector with the inner dielectric butted right up against the solder post. This is where the problem originated.
I theorized that the internal geometry of the Neutrik NP2X plugs—which features a tightly-fitted cup and boot—was the culprit:
“It’s the way it sits in the cups. Sometimes it touches. Like when you put the boot on it goes into compression and jams it right up to the solder cup.”
When the cable was compressed by the tight Neutrik boot, the exposed, conductive sub-shield was being pushed into contact with the tip solder cup—creating a partial short circuit to ground (the shield). This resistive path to ground is the definition of signal loading, which robbed the high-impedance guitar circuit of its precious voltage and necessitated the hefty 15dB boost. The generic connectors, by chance, had just enough internal clearance to avoid this fatal contact.
The Professional Solution
The specifications confirm the necessity of a careful strip: Note: This conductive layer must be stripped back when wiring, or a partial short will result.
The fix was straightforward: cleanly peel or strip back the black, conductive PVC layer a small amount, ensuring it cannot make contact with the tip solder cup when the connector is fully assembled. This prevents the short and restores the cable’s proper functionality.
My colleague quickly confirmed the successful result:
“The issue was in fact the conductive PVC layer.”
“fuck yeah, nailed it!”
This experience serves as a powerful reminder that even seasoned professionals must respect the specific design and termination requirements of high-quality components. When troubleshooting audio problems, sometimes the most unusual solution is found not in a faulty part, but in a necessary step that was, literally, not in the wire.
