This month
is third of a series discussing electronics inside your
guitar. Previously we discussed how pickups switches, jacks
and pots operate. It will help greatly if you read the
first two articles as the information contained in them
is a great foundation for understanding the material contained
here. The first two articles can be found in the Metro
Music Mayhem archives. Let's begin by discussing what can
be done with pickup wiring and combinations. I am not going
to go into the actual physical wiring of the pickups, but
will try and explain conceptually what occurs.
PICKUPS
As was stated in the first article, the most common types
of pickups are single coil and humbucking, either of which
can be passive or active. Also common is the piezo pickup
utilized for its ability to reproduce acoustic guitar sounds.
Since we now understand how each of these types of pickups
function, let's discuss what happens when they are used
in combination with each other. With the exception of arch
top jazz guitars and of course the guitar Eddie Van Halen
used early on, most guitars have more than one pickup installed.
The first thing we notice is that it is best to use pickups
of the same type as in all passive or all active. Without
taking further measures, mixing active and passive pickups
will not sound very good if they are both used at the same
time. The reason for this is impedance mismatching. The
output of an active pickup is low impedance and passive
pickups are high impedance. Each type of pickup uses different
value tone and volume controls to optimize tone and level.
When they are combined together the low impedance active
circuit will load down the high impedance passive circuit
causing loss of high end and output level. If it is really
desired to combine active and passive pickups in a single
guitar there are two practical ways. The first is to put
the relevant value volume and tone controls with each style
pickup and use them independently of each other. There
are Les Paul players who never use the pickups in combination
so this would work for them.The second way is to lower
the impedance of the passive pickup down to the active
pickup impedance so they will combine well together. This
can be done by adding a buffer circuit to the output of
the passive pickup. It will require a battery but you already
have one installed for the active pickup so power could
be taken from it to run the buffer. Purists should bear
in mind that the addition of a buffer to a passive pickup
will change the way it reacts with the amps input circuitry
possibility altering any of the attendant Mojo associated
with it. The actual tone of a pickup is determined by the
combination of the tone and volume pots, cable capacitance
and the amp's input circuitry as they are all parallel
resistive capacitive and inductive loads on the pickup.
Inserting a buffer into this combination of variables may
make the sound better... or worse.
Piezo pickups should always be used with a buffer to bring
them down to low impedance because not only is the impedance
of the piezo pickup too high to combine with a passive,
it is too high for the input impedance of most amps causing
a mismatch with the input circuitry. Adding a buffer to
the piezo will also let it mix with active pickups but
the same problem remains when mixing a piezo with passive
pickups, its buffered output is too low an impedance.
Now let's look at some possible pickup combinations:
SINGLE COIL
Let's use as an example a Stratocaster containing three
passive single coil pickups installed using a five way
pickup selector switch. Our choices here are each pickup
by itself plus the combinations of bridge and middle or
neck and middle. Along with each of each of these choices
comes a very unwelcome guest, HUM. But have you ever noticed
that on some three single coil pickup guitars in the positions
where two of the pickups are combined together most of
the noise drops out to a humbucker like noise level? How
is this possible as we are using single coil pickups that
are not able to reject hum? The explanation centers around
a different type of middle pickup. Let's explain it like
this: Suppose we remove the single coil bridge and middle
pickup from the guitar and replace it with a single humbucker
in the bridge position and leave the middle position empty.
For the moment ignore the neck pickup. When using the humbucking
bridge pickup the guitar now has little hum. As stated
in our earlier explanation of the humbucker it consists
of two coils in series that are wound opposite each other
combined with placing each coil in an opposite polarity
magnetic field in relation to the other coil. Now suppose
we had the ability to leave the coil closest to the bridge
alone but move the other coil and magnet until it is sitting
in the position a middle pickup would be located. We still
have a humbucker as it satisfies the opposite coil and
opposite magnetic polarity requirements, but now have a
coil located in the bridge and middle positions. This is
almost what is happening on the guitars with single coils
where the noise is reduced when pickups are combined. What
is really done is the set of three single coil pickups
contain a middle pickup whose winding direction and magnet
polarity is the opposite of the other two pickups. Therefore
when it is combined with either the bridge or neck pickup
we get a humbucking effect. One difference here from the
actual definition of humbucker is that the coils are in
parallel with each other rather than in series as in an
actual humbucker. This creates two effects. First, the
ability to reject noise in relation to signal is less than
a series wired humbucker, because the signal voltages of
the two coils don't add together as when they are in series
serving to raise the signal voltage further above any induced
noise voltage. Second, the inductance doesn't add either,
which leaves more highs to be able to reach the output
and creates a more single coil like sound.
HUMBUCKER
There are several ways we utilize a humbucker outside
of wiring it up as a straight humbucker. If your pickup
has a single coaxial cable coming from it as in an old
style humbucker there is really no other option with this
pickup, it must be hooked up the way it is. But on many
modern humbuckers we see four wires coming out of the pickup
enabling alternative wiring options. These four wires are
the start and finish wires for each of the two coils so
the assembly can be thought of before any wiring is done
as two single coil pickups sitting right next to each other,
each sitting on an opposite polarity magnet. There is no
industry standard for pickup wire color, so you will need
a chart from the pickup's manufacturer to tell you which
color wire goes where.Even if they only tell you how to
wire as a regular humbucker, the other wiring options can
be deduced. Let's look at some alternative wiring options
for the humbucker.
PARALLEL HUMBUCKER
This is exactly the same as what we discussed above concerning
the reverse wound reverse polarity middle pickup combining
with the single coil bridge pickup except we do it with
the two coils of the humbucker. Again, this is very close
to a regular humbucker but instead of the two coils being
out of phase in series they are wired out of phase in parallel,
giving us less output, more high end and more hum than
with a regular humbucker. But if you have a guitar with
a bridge humbucker and two single coils, a switching option
to wire the humbucker in parallel gives a closer approximation
of a bridge pickup Strat sound with less noise.
COIL TAPS
A tap is a point on the wiring of a coil where wiring
is brought out from that point. On a four wire humbucker
one wire goes to ground from one of the coils, one is the
pickup signal output taken from the other coil and the
other two wires are connected together to combine the two
coils in series. These two wires are also the midpoint
of the two coils.They are normally soldered together and
taped off but if a switch is put in that when thrown will
connect those two wires to ground, the coil between the
midpoint and ground is shunted out leaving only the other
coil which now becomes a single coil pickup. This is nice
on guitars with single coil middle and neck pickups because
it gives the option of three single coil pickups. On a
two humbucker guitar coil tapping both pickups will have
a Telecaster type effect. Remember though, that when the
pickup is used in the tapped position its output will drop
and noise level will go up. It is a little more complicated
wiring but it is also possible to tap the pickup so the
coil between the signal output and midpoint is the coil
shunted out in tap mode if that sounds better to you or
is the coil that will create a humbucking effect when combined
with another pickup.
SERIES IN PHASE HUMBUCKER
As mentioned before how the humbucker works is to put
its two coils out of phase in series having the magnets
flip the phase back. Therefore the wiring option of the
two coils in phase in series is not something that will
be useful. It will create a thin sounding, low output pickup
with lots of hum.
SWITCH WIRING
Alternative wiring options can be a useful tool to expand
the range of sounds coming from the guitar. But the more
options you have require the ability to access them in
an easy fashion so they can be utilized while you are actually
playing. This is where the pickup selector switch is important.
On Strat style guitars there is a three or five way switch.
But the switch also contains a second set of terminals
(poles). This is the same as two independent switches that
are controlled by the same switch lever (called a double
pole switch). The first row of terminals routes the choice
of pickup combinations to the output jack. The second row
can be utilized to engage a coil tap or remove a tone control
etc. at certain positions of the switch. For example you
could wire the humbucker normally when it is used by itself
but engage its coil tap to come on automatically when it
is combined with the middle pickup for a classic Strat
sound. There are some specialty switches that have a third
set of terminals if you have the desire to build in a lot
of switching options such as adding the ability to use
the neck and middle pickups together on a Strat for a Tele
style sound.
A Les Paul style guitar has less ability to vary from
the stock switching. It uses a single pole pickup selector
switch which does not allow any switching options. There
are two other ways to enhance switching on this type of
guitar. First you can add toggle switches, but these require
drilling into the front of your 59 cherry sunburst Les
Paul Standard. I don't think so! The better option is to
replace the tone and volume pots with pull pots and wire
the switching options to the switches on the pot. Then
for example a coil tap can be activated by merely pulling
the knob on the pot up.
One resource I can direct you to for guitar wiring is
on the Seymour Duncan web site. He has really nice wiring
diagrams for just about any pickup combination you desire.
But be realistic about your soldering skills before you
start modifying. Guitar wiring looks simple, but if your
soldering is not professional you are going to make a mess
of your guitar. We see this often at our shop.
REPLACEMENT PICKUPS
Be careful when replacing pickups on guitars with a different
brand than what was originally installed. There is a chance
that the new pickup is out of phase in relation to the
other brand of pickups still in the guitar. In other words
the new pickup would work fine with others from tits same
brand but not with the ones you already own. A simple solution
is to reverse the phase of the new pickup in relation to
the others. This is easily done on pickups when all coil
wires are accessible. But if you have a clone of a vintage
pickup where one side of the coil is hooked to a braided
shield this is not possible because using the shield as
the positive out will cause noise especially when the pickup
is touched. The solution here is to reverse the phase of
the other pickups. Remember phase is a relative term applying
to the phase relationships between the pickups. It doesn't
matter how the total phase of the system is wired as long
as all the individual elements are in phase with each other.
There are quite a few possibilities to pickup wiring.
You can experiment all you want but there are two sides
to this. You may come up with a new and novel tone that
works well with your playing style, but if you are looking
for conventional tones realize that most of the time the
sounds you hear and desire are coming from conventionally
wired guitars. Looking aside from tone, these conventions
also work well as far as deriving the least hum and highest
output and bandwidth.
Steve Weiss is the owner and main technician
of Steve Weiss Electronics Inc. He is experienced in
the repair of analog and digital musical equipment.
This includes everything from Vintage Tube Amps and
Pro Audio equipment to Digital Keyboards There is also
a guitar repair shop staffed by some of the areas top
guitar repair techs. He is authorized for warranty
work on most major brands. Steve Weiss Electronics
is located inside of Sam Ash Music at 5460 West Sample
Road Margate, FL 33073 954-975-3390 Ext 272. Steve
has also spent 25 years on the road as a performing
guitarist and is the designer of Primal Guitar amps
that can be seen at Primal
Audio.com Steve can also be reached at stevew@metromusicmayhem.com |
|
|
