Acoustic Guitar Endpin Jacks
By Steve Carmody
Acoustic guitar endpin jacks can be a mystery, until you see them removed and installed
Inside all acoustic guitars there is a block of wood which anchors the sides at the bottom
of the guitar body. This is referred to as the endblock. On the outside of the guitar, a
strap button is often located in this area. On acoustic guitars with electronics installed,
endpin jacks are located at this spot. The jack itself is a two-stage threaded barrel
with a wide ( usually around 13mm outer diameter) long shaft which seats inside the guitar
endblock, and a narrower shorter shaft which extends outside the guitar. There is a nut on
the inside and a nut on the outside which, when tightened, compress against the guitar
endblock. Finally, there is a flanged cap which threads onto the shorter narrower shaft
and covers the outer nut. This flanged cap also serves as a strap button.
The photo below shows what the installed endpin jack looks like from the outside.
Here is a photo which shows the basic mechanical workings of the style of endpin jack used with
most American made guitar electronics. Inside the wider part of the jack are metal tabs
which connect to the various wires associated with the pickup and pre-amp ( ground, signal
lead, battery ground).
The first step in removing the jack is to unscrew the strap button cap which
covers the outer nut. Sometimes this cap is finger tight and can be unscrewed by
hand, but in other cases it must be loosened, carefully, with a pair of pliers.
Once this cap is removed the outer nut can be loosened.
Since the shaft can spin if it is not held in place, a small hole has been
drilled in the outer threaded shaft so that a tool (here I am using an awl) can be
inserted to prevent the shaft from spinning as the nut is loosened
(or tightened) with a thin crescent wrench. Once the nut is removed the jack can be pushed into
the guitar and removed. Installation is the reverse of this process.
Even on large body guitars removing or installing the jack from the inside can
be a challenge, so I like to use a wooden dowel stick. This is a 5/16" dowel
stick which I tapered at the end. I also wrap a bit of masking tape around
the end, which helps to keep the jack from falling off as I move it into and
out of the hole at the end of the guitar.
Once the outside nut has been loosened and removed I can use the dowel stick to
push the jack into the guitar and up to the soundhole where I can either remove it
or adjust the inside nut, as
necessary. Then I can use the dowel to draw the jack back through
the guitar and into the endpin hole.
There are a couple of common maintenance issues related to endpin jacks.
problem is that one or both of the nuts comes loose, allowing the jack and the
associated wiring to move around. If the inner nut has become loosened, the outer
nut can be fully tightened and yet the jack is still loose. In this scenario the inner
nut must be tightened until the wider long part of the jack is fully
inside the endblock. If any of this part of the jack extends outside the the guitar,
the nut on the narrow part of jack will not compress against the guitar and the jack
will be loose. It should be noted that if too much of the narrow portion of the jack
is inside the endblock, and the jack strap flange is installed, the guitar plug will
not fully insert into the jack, and there will be no signal.
On occasion, the outer cap/strap button flange will
loosen, even though the two nuts are correctly situated, and prevent the guitar cord
from fully inserting into the jack. This is also often
the cause of "no signal" issues. In this case, just tightening the cap
will correct this problem.
Another common problem is that, over time, the signal, ground and battery
contacts ( metal tabs) inside the jack can become fatigued and the signal from
the guitar will crackle or cut in and out when the guitar cord is moved. At this
point the jack must be replaced.
Steve Carmody is an independant guitar repairman and luthier with a shop in Silver Spring, Md.
He has been doing guitar repair and restoration full-time since 1990.
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