Fig. 1. With its large ceramic elements and innovative carrier design, the Takamine Palathetic
pickup installed in their PT-007S was the answer for touring guitarists in the late ’70s looking
for a hassle-free acoustic without feedback issues.
Fig. 2. Conventional undersaddle pickups
have relatively small piezo-ceramic elements that are sandwiched between the bottom of the
saddle slot and the bottom of the saddle.In my last column [“Saddle Up, Amigo,”October 2012] we talked about some of the
early pioneers in the development of amplified
acoustic instruments. This month, let’s dig into
the inner workings of the Takamine PT-007S,
one of the earliest—and most successfully integrated—amplified acoustic guitars.
Takamine first introduced the PT-007S in
1979, and the model was an instant success,
especially among touring guitarists playing in
the bigger country groups out of Nashville.
Factory equipped with Takamine’s new
Palathetic pickup and an onboard, battery-powered
preamp/EQ, the guitar was a no-hassle,
plug-and-play acoustic that could perform
onstage at high volumes without feedback.
Taking a closer look at the design of
the pickup in Fig. 1 will help us understand
why this guitar was able to perform
so well onstage in a high-volume setting.
Like conventional undersaddle designs, the
Takamine pickup employs six individual
piezo-ceramic elements. This, however, is
where the similarity ends.
In more conventional undersaddle pickups
used by most manufacturers (Fig. 2), the
ceramic elements are quite small. Located
directly under the saddle in a normal bridge
slot that has been deepened to accommodate
the height of the pickup, the ceramic elements
are sandwiched between the bottom
of the saddle slot and the bottom of the
saddle. The saddle is not glued in or press
fitted, but rather, allowed to slide in the slot.
As the strings vibrate, the saddle acts like a
piston and transfers the resulting change in
force directly to the sensor.
With the Takamine design, one of the first
things we notice is the very large size of the
ceramic elements, compared to more conventional
designs, as well as the large die-cast
metal carrier that holds the elements. This
carrier aligns the elements with the strings and
is attached to the bridge plate with screws that
engage a metal strap, which is located in the
saddle slot directly under the saddle. The cylindrical
elements are allowed to pass through
holes that are drilled through the bridge plate,
soundboard, and bridge, and they are sandwiched
between the die-cast carrier and the
metal strap. This larger design, according to
Takamine, offers up to 12 times the element
mass of a typical undersaddle pickup.
Before we continue, let’s review some
fundamental principles of operation for
piezo ceramics. This will provide a better understanding of why these unique design
elements play such a large role in the ability
of Takamine’s acoustic/electric guitars to perform
at high volumes without feeding back.
Piezo transducers are like any normal capacitor
where two conductive surfaces are separated
by an insulating material. In the special case of
piezoelectric materials, the insulating dielectric
material will generate a charge when subjected
to mechanical strain. This mechanical strain
occurs when the piezo material is deformed
by being in intimate contact with a vibrating
material. And the efficiency of the transfer of
these changes in force, created by the vibrating
body, is greatly influenced by several factors.
In some designs, the sensor becomes an
accelerometer when it is simply glued to the
face of the vibrating surface and is loaded
with a mass. Without the mass load, and if
the piezo element is thin enough, the element
becomes a bending mode sensor, such
as a typical bridge-plate transducer.
With Takamine’s pickup, however, the
sensor is a compression-mode force sensor.
This means that the sensor is excited by the
compression forces created by the piston
action of the saddle, which squeezes the
sensor against the die-cast holder.
One factor that greatly determines the output
character of a transducer is the nature of
the material that directly contacts the sensor.
Sound is a vibration of kinetic energy, passed
from molecule to molecule within a material.
And every material that transfers vibration is a
mechanical filter. The unique, elastic properties
and the density of these materials have
a significant effect on the manner in which
sound propagates through them.
In the course of my design work, I have
found that the size of the sensor elements is
influential in determining the sound factor as
well. It’s like a salad: Add a little onion and it
brings some flavor to the other ingredients.
Add a lot of onion and it becomes an onion salad. In pickup design, if the sensor is relatively
small and is in direct contact with the
wood itself, the resulting output of the sensor
is dominated by the resonant characteristics of
the wood. On the other hand, if the sensor is
relatively large and is separated from the wood
by non-wood materials, the resonant characteristics
of the sensor and the other materials
become dominant.
Let’s put this all together: In the case of
the Takamine design, the vibrating strings
create a changing force on the saddle, which
efficiently transfers this force through a thin,
metal plate—directly at one end of the massive
ceramic element that is supported on
the other end by an equally massive die-cast
support structure. Although the ceramic elements
pass through holes in the bridge plate,
top, and bridge, the coupling to the top
(which is highly resonant and the source of
feedback when interacting with a sound reinforcement
system) is minimal. The downside
of this design is that the amplified sound—
though very stable and predictable—is somewhat
less complex and acoustic than it would
be if the sensor coupled more intimately with
the wooden structure of the instrument.
Taken as a whole, this early example of a
fully integrated, acoustic/electric instrument
was a resounding success. The combination
of a heavily braced top, a decoupled piezo-bridge
pickup, and a fully integrated onboard
preamp were exactly the right elements in
making the PT-007S such a great working
tool for high-volume stage environments.
Hats off to Takamine for their early
innovation and a job well done!
Larry Fishman holds more than 30
patents in transducer and musical
instrument design. He is president
and founder of Fishman Transducers,
which he began in his garage in 1981.
In the early ’90s, he also co-founded
and managed Parker Guitars (which
was later sold to U.S. Music Corp.) with his friend
Ken Parker.