GUITARTECH
’Bucking Hum and Then Some
I was recently put in a position where I
had to know a great deal about PAF pickups. Like most guitar players, I have a tendency to say “I can fake my way through
it,” but the stakes in this case were way
too high to not be honest with myself. So
off I went to the woodshed with the intention of learning everything I could about
PAFs. I will fill you in on why I put myself
through this endeavor later, but I first want
to pass along the essential knowledge I
learned in the process.
So I don’t lose anyone at the bakery, let’s
begin with humbucker basics. In any
magnetic pickup, a vibrating guitar string
induces an alternating voltage in its coils.
However, magnetic coils are also antennas
and are therefore sensitive to the electromagnetic interference that can be generated by wiring and various electrical appliances. Guitar pickups collect this noise,
which can be quite audible, sounding like a
constant hum or buzz.
A humbucker has two coils with opposing
windings and polarities. The string motion
induces current in both coils in the same
direction. Electromagnetic interference, on
the other hand, induces current in opposing directions in each coil because of the
reversed winding and polarity. When the
signals from both pickups are combined,
the noise is cancelled and the actual signal
is increased, dramatically improving the signal-to-noise ratio. This technique is called
common-mode rejection by electrical engineers and is also used for balanced lines in
audio recording.
Before the invention of the humbucker,
guitarists relied on single coil pickups, like
Gibson’s P- 90, which did nothing to block
the dreaded 60-cycle hum. In the mid
1950s, Gibson engineer Seth Lover was
assigned to tackle this problem. Seth connected two single coil pickups in series,
as opposed to parallel, and connected the
coils out-of-phase, both electrically and
RICK WHEELER
magnetically – thus the signal noise of one
coil canceled out that of the other, which
is ultimately how the pickup came to be
known as “humbucking” or humbuckers. Seth and Gibson filed their patent for
the pickup design on June 22, 1955, and
Gibson added the new pickups to steel
guitars in 1956 and on electric solidbody
and archtop guitars – including the Les
Paul Model – in 1957. During late 1957, a
small black decal with gold lettering was
added to the underside of the pickup that
read, “PATENT APPLIED FOR” and the PAF
designation was born.
Each humbucker has a bobbin wound with
a certain type of wire. On original PAFs
the bobbin wire appears purple, versus
later PAFs that have a reddish appearance. Additionally, different types of wires
had unique coatings. When wire coatings
change, the sound of the pickups also
change. The amount of wire and coating
wound on each bobbin helps to determine
the pickup’s resistance. When the bobbins are wound with more than a nominal
amount of wire they become more powerful, offering fatter midrange at the expense
of treble response. The people running the
pickup winding machines used by Gibson
from 1956-1961, whether knowingly or
unintentionally, were inconsistent with the
numbers of windings. The machine operators essentially estimated when a pickup
bobbin reached 5000 turns of wire, which
ended up giving each set of PAF pickups a
unique sonic character.
I had to learn all this info because Larry
Carlton wanted to replace the original humbuckers in his number two 335, a ‘ 68 that
has been previously used as the backup
guitar for his famous ‘ 69 model, played on
over 200 number one hits. Knowledgeable
techs told me to look for the “PATENT
NO.” style with unopened nickel-plated
covers, or, better yet, a pickup with the
“PATENT APPLIED FOR” decal intact,
which are highly valued and harder to find.
Here is what I was specifically looking for:
original PAFs made in 1956 or 1957 that
had a long magnet, no PAF sticker, purple
bobbin wire, black leads on both coils,
brushed stainless steel covers, Phillips
screw bases, ohms ranging from 7k to 9k,
black PAF-style bobbins, and L-shaped tool
marks on the feet; original long-magnet
PAFs made from 1957 to 1960 that had
“PATENT APPLIED FOR” stickers, purple
bobbin wire, black leads on both coils,
nickel covers, Phillips screw bases, ohms
measuring from a low of 7k to a high of
9k ohms, black PAF-style bobbins and
L-shaped tool marks on the feet; or a set
of the final batch of PAFs made in ‘ 61 or
‘ 62 that featured a short magnet, “PATENT
APPLIED FOR” sticker, purple wire, black
leads on both coils, nickel covers, Phillips
screws on the base, double black bobbins
and the L-shaped tool marks.
I knew if I found any of these and their
measurements were good, we were in
business. Lo and behold, we found a
matched set made in 1960 and put them
in the ‘ 68 335. They sound amazing. Lately,
Larry has been touring with “number two”
exclusively, due to the sound of those pickups. It was a great learning experience for
me and the end result was that the world
gets even more from Mr. 335 himself,
which we can all enjoy.
Rick Wheeler
Rick Wheeler currently works as Larry Carlton’s guitar tech and front of
house engineer. He is also an accomplished jazz guitarist, vocalist, and
educator. You can contact Rick at rickwheeler@hughes.net
