Output Jack Considerations

In this article, Pete Biltoft at Vintage Vibe Guitars goes in-depth on the simple, often overlooked output jack.

Thanks again to Pete for the permission to post this here!

September 2013

Howdy!

The topic for this tech tips newsletter is the all-important output jack.

While there are a few different styles of output jacks have been used in electric guitars and basses including cables with XLR connectors, ¼” stereo output jacks and 1/8” size mono and stereo jacks, for the purposes of this newsletter I plan to focus on the industry-standard ¼” mono output jack. I quite often use output jacks manufactured by Switchcraft and unless specified otherwise in this discussion I will be referring to the Switchcraft model output jack designed for strat, tele and Les Paul style instruments.

This simple and often overlooked component provides both a mechanical and an electrical interface to the guitar cable and is one of the most frequent causes of electrical issues in an electric guitar or bass.

I. Mechanical considerations:

As a mechanical interface to the guitar cable, the output jack is designed to capture and hold the tip of a ¼” guitar cable plug and also to release the plug when pulled. A simple formed metal tab or prong with a “V” shaped feature at its end engages a groove near the tip of the guitar cable plug. The straight section of this tab functions as a spring flexure. Over thousands of uses there are a few possible failure modes in the output jack including:

1. The flexure can become bent or fatigued and lose its ability to securely hold the guitar cable plug in place.
2. The conductive metal coating on the tip of the formed metal tab can be worn away and the base metal can corrode which may compromise the electrical connection with the guitar cable plug.
3. Foreign material (dirt, grease, fine particles or sand) may accumulate on the prong compromising the electrical connection by causing either a short or open circuit.
4. In some cases there is insufficient space available in the output jack cavity of the instrument for the prong to flex during insertion of the guitar cable plug; this can cause partial engagement of the plug and both an unreliable mechanical and electrical connection between the plug and the guitar cable.

At the initial installation of the output jack in the instrument I suggest double-checking that there is sufficient space for the prong to flex and that there are no materials in this area which can become loose over time including connecting wires or grounded copper shielding.  Occasional inspection of the output jack would reveal the presence of wear or debris that could impair reliability.

Another mechanical interface associated with the output jack is the connection between the output jack and the instrument. In strat style guitars the output jack is often secured to a formed metal plate by a thin ½” hex nut, dress washer and perhaps a lock washer. If a lock washer is not provided with your output jack you can use one of the lock washers designed for standard size volume or tone control pots. In most cases one must solder the “Hot” (signal) and ground leads to the appropriate tabs of the output jack prior to installation (more on this later). Take care not to pull or twist the wires soldered to the tabs of the output jack when tightening the locking nut. I use a ½” nut driver or socket wrench to tighten the locking nut. More sophisticated tools designed specifically for this purpose are available from guitar parts suppliers such as Stewart MacDonald.

In tele style instruments the output jack is often connected to a chrome, nickel or gold plated formed metal cup or a machined aluminum plug. In Les Paul style instruments the interface with the output jack is frequently a bent metal plate. Most of the comments previously made regarding the strat style mounting plate and those mounting plates used in tele or LP style instruments apply.

II. Electrical considerations:

The ¼” mono output jack is considered a “polarized” electrical component in that one must correctly assign the two tabs for electrical connection to the leads from the instrument’s controls circuit. Improper connection of the leads from the instrument’s controls circuit to these two tabs can cause a wide range of undesirable outcomes including: no signal to the amplifier, failure of the instrument’s grounded shielding and possible electric shock to the player of the instrument from a damaged or ungrounded amplifier. Careful inspection of the Switchcraft ¼” mono output jack will reveal that the two tabs designed for electrical connection are different; one has small corners or “shoulders” near the end of the tab where the hole is located and the other does not. In the output jacks I use, the tab without the corners is formed from the same piece of metal which connects to the cylinder of the output jack into which the guitar cable plug is inserted. These form the electrical ground interface surfaces and this tab should be connected to a ground lead from the instrument’s controls circuit. The tab with the small shoulders near the hole is the “Hot” tab which is electrically connected to the formed metal prong of the output jack which contacts the tip of the guitar cable plug. This tab is where the hot signal output lead from the guitar controls circuit should be soldered. If there is any doubt about the assignment of these two tabs I suggest using a multimeter set to indicate continuity to double-check. When I make solder connections to these two tabs I typically slide a 1” length of shrink wrap onto the leads and I pre-tin both the stripped end of the leads and the output jack tabs prior to making the solder connections. Once the connections are made and tested I use a hot air gun to shrink the shrink wrap into place forming a reliable layer of electrical insulation around these solder joints.

After installing the output jack into the instrument it may be wise to test the interface under playing conditions. With the instrument complete and ready to play, plug a guitar cable into the instrument and the other end of the cable into an amplifier, turn the amp on and wiggle the guitar cable at the interface of the cable and the output jack. If all is good you should hear no “popping”, “crackling” or static noises and should experience no drop out in volume while playing. If during use the guitar cable is harshly jerked out of the output jack repeatedly I recommend inspection and preventative maintenance of the output jack during down times between playing of the instrument.

I hope you find this information useful.

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Best wishes,

Pete Biltoft

Vintage Vibe Guitars
website: www.vintagevibeguitars.com
email: [email protected]