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Digest of Theory and Construction of Electric Pickup articles
===========================================================================
There have been many excellent how-to-build your own electric pickups
posts on the net. I saved very few of them. Please provide me with
an archive or pointer for inclusion here.
Thanks!
Tim Stanley
===========================================================================
Newsgroups: alt.guitar
From: META000 <META@UNB.CA>
Subject: humbucker theory (was Ibanez hum)
In the early 80's, Jeff "Skunk" Baxter used to write a column for
Guitar Player. In one issue he explained how to improve the noise
and hum on humbuckers.
First, the theory. Hum"buckers" provide a virtually hum-free sound
by providing two "antenna's" for 60-cycle hum and RF, which are
electrically opposite to each other. When the hum and RF picked up
by one coil are combined with the hum and RF picked up by the other,
the two cancel each other out. Fortunately, for us, the sounds
picked up from the strings themselves don't cancel out entirely, and
the result is a hum-free, meaty sound.
In order to be able to accomplish this, the two coils have to act as
equivalent "antenna's". This means that the magnetic field in each
coil should be equivalent, and the coils themselves should also be
of equivalent impedance.
Althoughthe technology for producing pickup coils is pretty damn
good, there are sufficient differences that occasionally crop up,
such that the two coils in one "humbucker" are not matched enough to
buck the hum completely. It's my understanding that the factory
folks often take coils off the line and sort them into bins with
specific impedance ranges. Any two coils from the same bin will be
much more alike in impedance than two coils from separate bins.
Fine. IF it happens that somebody ain't doing their job right, you
can end up with a pickup where the impedance of one coil is a bit
different from the other. We're talking a few per cent here, but
not much more. Let's give the folks who work for Larry and Seymour
a bit of credit!
If you are delicate and graceful with a soldering iron, you can
improve the tone and noise/hum of your humbucker in the following
manner:
1) Remove the pickup entirely from the guitar (sorry).
2) Detach all relevant leads so that you have exposed two contacts
for each pickup coil.
3) Get hold of a 4 1/2 digit ohm-meter (3 1/2 may not be precise
enough), and measure the electrical resistance of each coil.
4) If they are within 1% of each other (e.g., one coil is 5000 ohms,
and the other is 5050 ohms), then any annoyingly loud hum may not be
coming from your pickups (although there are exceptions to this).
5) If they are more than, say 0.5% different, take the coil with the
greater resistance, and GENTLY! lift the wire at the end of the coil
(i.e., on the outside) and unwind it approximately ONCE for each
ohm, until you have reduced the coil resistance by thedifference
between the two coils (e.g., if you needed to reduce the 5050-ohm
coil in the above example, take off about 46 turns) scrape the
insulation off at the appropriate part and measure the new
resistance. When the two pickups are within 0.1% of each other,
you'll have done about the best that can conceivably be done. I did
this with a home- brew "stacked humbucker" I made, and I can
practically stick this thing on the damn power transformer, and not
hear any hum. We're talking VERY quiet.
6) Once the two coilsmatch, put the pickup back together, making
sure that the appropriate phase relationship between the two coils
is restored to its original state. If the two coils are
electrically in phase, no hum-rejection will occur.
This is obviously delicate work, and time-consuming. It is also one
of the reasons why pickupsof any quality cost big bucks.
Jeff Baxter was quite laudatory of this procedure, as am I. We both
stress the delicate nature of this. Pickup coils are easy destroy,
if you don't know what you are doing, so be careful.
Mark Hammer (aka META)
---------------------------------------------------------------------------
Newsgroups: alt.guitar
From: META000 <META@UNB.CA>
Subject: humbucker theory (was Ibanez hum)
Organization: The University of New Brunswick
Date: Sun, 4 Oct 1992 22:42:56 GMT
As usual, Don and R.G. set me straight. (Maybe it's true. Maybe you
DO need an engineering degree to be a musician these days!)
I might point out that my windings are VERY sloppy. When I say
handwound I mean HAND wound. I hold the coil in one hand and the
wire in the other. I suspect that, taking R.G.'s calculations about
length of turn into account, we really ARE looking at a 10%
difference in turn length between inside and outside turns.
Don mentions the phenomenon whereby pickups attain their
characteristic sound by virtue of variations in the magnetic
relationship between string and polepiece, and how the amount of
string length within the "eye" of the pickup determines timbre. I
assume that when the wave length of a note is such that "upsy" and
"downsy" parts of that wave are each within the "eye" of the pickup
(or both "eyes" in the case of humbuckers), then the two components
cancel each other, leaving only those string vibrations that are
uniquely represented at the pickup. Peaks and troughs of high
frequencies are so close together that they are usually somewhere
within 180 degrees out of phase over each polepiece, giving the
meaty, but lustreless, sound of a humbucker.
I understand why the dimensions of the humbucker have become a standard
of sorts these days, given how desirable it is to be able to buy a
pickup and just pop it in. Standards for cavities need not imply
standards for coil-spacing and voicing, though. It seems to me
that given how capable we've become at making eensy weensy
coils that can fit two to a single-coil-case, its surprising that
someone hasn't tinkered with an adjustable voicing pickup to fit in
a standard size humbucker chassis. Technically, itought to be
possible to make two small coils,one of which could slide backwards
and forwards inside the chassis, resulting in the cancellation of
different frequency components. The Fender humbucker (that showed
up on Starcasters and Tele's), has two sets of adjustable polepieces
so that one can create "angular" polepiece alignments (like a
Tele-bridge pickup in a humbucker case). With one moveable coil
within a humbucker chassis, it ought to be possible to do the same
thing with one of the coils; i.e., one perpendicular to the strings
and one slightly offset at an angle. The old Dan Armstrong guitars
(the see-through plexiglass ones) had a track along which a pickup
could be slid forward or backward to a different position to get
different "personalities". The Turner guitar that Lindsay
Buckingham plays has a pickup that can be rotated to different
angles within its' housing. So, the idea of "redefinable" pickups
is not new. I guess people are just to used to looking at double
coil pickups in a certain way.
Another idea I had for a pickup, and just never got around to
making, was a "coil-swapping" pickup that utilizes 3-coils, two of
which may be swapped to produce either a side-by-side humbucker or a
stacked humbucker. I discussed the idea with the guys atEvans
pickups, when I used to live near them a few years ago. Evans said
that, in theory, it ought to work, but that he and many others, found
the sound of stacked humbuckers less than desirable. Still, it
strikes me as an idea that might prove ideal for somebody,
somewhere. The basic rationale is this. Many guitarists try to get
a "single-coil sound" by cancelling one of the coils on a humbucker.
Although this does eliminate the within-pickup cancellation of high
end that usually occurs, it also results in a noticeable drop in
output, and loss of hum-rejection. I thought that if the (please
don't hurt me, Don) IMPEDANCE of the pickup could be kept constant
when switching to single coil mode, then the drop in output would be
reduced (although still there to some extent). If that extra
impedance could be provided by an additional coil in hum-bucking
mode, so much thebetter. Admittedly, I haven't tried anyone else's
stacked humbucker, and it's been so long since I've played with other
musicians, that I don't know if the stacked humbucker I made is some
kind of freak of nature, or whether my standards have drifted so far
that I actually like what others dislike immensely. In any event,
it functions just fine as a pickup, disregarding aesthetic
prferences. If one stuck it in a chassis alongside another coil, so
that, from the side, it looked like two humbuckers, piled on each
other, with an empty bobbin on the bottom of one side of the pickup,
you'd have my coil-swapping pickup. Let's say that the rear pair of
coils form a stacked humbucker. If the bottom coil of that pair is
replaced by the coil at the other side of the pickup, we now have
(assuming they are wired the right way), a traditional side-by-side
humbucker. Alternatively, if it's true what they say, that stacked
humbuckers really suck, then one could always try the following.
Wind a standard single coil Fender-style pickup, but tap it after
half the turns. Since many of the turns would be at both magnetic
poles (i.e., the north and south ends of the polepieces), this
tapped coil, in tandemwith the extra coil on the front of the pickup
(where all the turns would be primarily at one magnetic end) should
constitute a reasonably, but not perfectly hum-rejecting pickup.
When the extra coil is deleted and replaced with the remainder of the
windings on the main coil, we should get a standard single coil
sound, hum and all.
There you go, some ideas for novel pickups.
Now, if someone could only explain to me how Lace pickups reject
hum.
Mark Hammer
---------------------------------------------------------------------------
Newsgroups: alt.guitar
From: META000 <META@UNB.CA>
Subject: Re: Bridge Pickup Alignment
Organization: The University of New Brunswick
Date: Sat, 28 Nov 1992 18:33:28 GMT
As usual, not much to add to Don's thorough explanations, except to
note that one of the interesting quirks of Jimi Hendrix's sound was
his Strat rear pickup. Since Hendrix used a right-handed Strat
- strung* left-handed (high E where the low E should be), the
location of the bridge pickup polepieces on his setup were
equivalent to taking a Strat and positioning the bridge pickup at
the exact opposite angle. (close to bridge at the top, away from
the bridge at the bottom, looking at the guitar head-on).
Some years ago, I memorized the pickup layout on a Strat wrong and
inadvertently installed just such a pickup arrangement on my
Epiphone Coronet that I was modifying.
So how did it sound, you're wondering?
Well, the thin strings sounded "meatier" than they usually do in
relation to the thicker strings, and held up somewhat better under
threat of wah-wah. On the other hand, the "sparkly" sound that
usually comes with front-rear combinations was sorely lacking. Of
course, it may have been the pickups themselves (a DiMarzio Fat
Strat at the bridge; aye caramba!) that produced the sound. In any
event, not being Jimi, and being somewhat partial to combined-pickup
sounds, I re-oriented the bridge pickup and found it to be more to
my liking. A bit thinner, yes, but capable of generating sounds
with more character.
As Don implied, the location of the polepieces along the vibrating
part of the string determines (along with picking style, etc.) which
harmonics will be more emphasized in the final output. If my
physics knowledge serves me, higher harmonics have a SHORTER
wavelength, while lower harmonics have a longer wavelength. That
is, when a note is plucked, the string has numerous different
vibrational patterns going concurrently, each covering a different
proportion of the string's length, and, more or less, superimposed on
each other (essentially high ones superimposed on low ones). The
thinner and more flexible the string (although I gather there are
some exceptions to this), the easier it is for the string to undergo
little teensy bends in this place or that (i.e., short wavelength
vibrations). So, all other things being equal, thinner gauge
strings are "brighter" than heavier gauge strings, because they can
vibrate at shorter wavelengths moreso than heavy gauge ones.
So what the devil does this have to do with bridge pickups?
Simple. For any two notes played, the same harmonic (e.g., the 5th
harmonic) for each will have a different wavelength (assuming the
two notes were different to start with), with lower notes having
a longer wavelength for the same equivalent harmonic. What this
means is that, for the SAME harmonic from any note played on the
lower pitched strings, compared to any note played on higher pitched
strings, you have to move further away from the bridge before you
can pick up that vibration on the string at its' maximum displacement.
Stated another way, the same harmonics on the high E as on the low E
(remember, this is the same OVERTONE and not the same FREQUENCY) can
be readily detected closer to the bridge.
So, since the bridge pickup signal consists of a lot more harmonic
content than the neck pickup, people like Leo Fender angled bridge
pickups to provide a more CONSISTENT sound over strings, rather than
provide some kind of special "hot-rodded" tone. The angling is a
simple but effective way to make sure that the same overtones in the
overtone series receive the same emphasis from string to string. In
the case of my "Jimi" configuration, the pickup was sensing the
lower overtones moreso in the high strings than it was in the low
strings, and vice versa for the higher overtones. Small wonder that
it sounded "meatier" on its' own, and did little when combined with
another pickup.
The Fender humbucker design, with the 12 adjustable polepieces (of
which 6 are visible from the outside) was intended to allow for
balancing harmonics like this by placing the polepieces for the low
strings that were away from the bridge higher up, and the polepieces
for the low strings that were closer to the bridge HIGHER up,
creating a humbucker that fit in the slot, could work for neck and
bridge positions, but could be configured to be a "functionally
angled" pickup.
Don is quite right in pointing out that an angled Strat pickup
provides different coverage of the strings than a non-angled one.
In the case of an angled humbucker (a la Eddie), a slight tilt ends
up producing more coverage of the strings, rather than less,
behaving somewhat similar to those Carvin pickups with the 22 pole-
pieces, by having a polepiece on either side of the string.
My guess is, however, that since a greater length of the string is
covered by the humbuckers two rows of polepieces, one ends up
sensing much more of the lower harmonics (since higher ones could be
out of phase between the two rows of polepieces), so angling of a
full size humbucker probably does diddley to the tone, but helps
give better evennness to the sound during pronounced string bends,
where the string ends up away from the polepiece.
Mark Hammer
---------------------------------------------------------------------------
From: dam@dcs.glasgow.ac.uk (David Morning)
Newsgroups: alt.guitar,rec.music.makers.guitar
Subject: Re: 2 Single Coils = Humbucker??
Date: 2 Apr 93 10:43:06 GMT
Organization: Glasgow University Computing Science Dept.
soh@gdstech.grumman.com (Scott O'Hare) writes:
>In article <bill.733624388@voodoo> bill@verdix.com (William Spencer) writes:
>>soh@gdstech.grumman.com (Scott O'Hare) writes:
>>
>>>how about recommendations for a humbucker that also sounds great
>>>in single coil mode?
>>
>>I just reviewed the DiMarzio MultiBucker here about a month ago.
>>
>I guess that means you liked it (?) Any other suggestions?
>Someone recently wrote that humbucking pickups are NOT simply two single
>coils placed side by side - I understand the bit about reverse polarity
>windings to cancel hum, but not the bit about having an integrated magnetic
>structure. The ones I've taken apart look alot like two separate pickups
>to me! Maybe the metal plate to which both singles are fastened connects
>the magnets in some way...
Think it was me. The 2 coils are the same as 2 single coil pickups but the
pole pieces from each coil reach down to make contact with opposite poles
of the actual magnet, so one coil is in contact with the north pole while the
other is in contact with the south pole. The magnet itself usually sits between
the 2 coils (well it does in my DiMarzio, I've seen others where the magnet
was thinner and 2 pieces of steel were used to extend the magnet's poles to
underneath each coil). I'll try and draw a x-section:-
Coil 1 Coil 2
--------- --------
| | | | | | | |
| | | | | | | |
---| |--- ---| |---
| |-------------| |<----pole pieces
-| N S|-
|pole Pole|
| Magnet |
-------------
Dave
---------------------------------------------------------------------------
Newsgroups: alt.guitar,rec.music.makers.guitar
From: jpmakela@klaava.Helsinki.FI (J Pekka Makela)
Subject: Re: 2 Single Coils = Humbucker??
Organization: University of Helsinki
Date: Fri, 2 Apr 1993 21:56:25 GMT
David Morning (dam@dcs.glasgow.ac.uk) wrote:
> soh@gdstech.grumman.com (Scott O'Hare) writes:
>
> >In article <bill.733624388@voodoo> bill@verdix.com (William Spencer) writes:
> >>soh@gdstech.grumman.com (Scott O'Hare) writes:
> >>
> >>>how about recommendations for a humbucker that also sounds great
> >>>in single coil mode?
> >>
> >>I just reviewed the DiMarzio MultiBucker here about a month ago.
> >>
>
> >I guess that means you liked it (?) Any other suggestions?
>
> >Someone recently wrote that humbucking pickups are NOT simply two single
> >coils placed side by side - I understand the bit about reverse polarity
> >windings to cancel hum, but not the bit about having an integrated magnetic
> >structure. The ones I've taken apart look alot like two separate pickups
> >to me! Maybe the metal plate to which both singles are fastened connects
> >the magnets in some way...
>
> Think it was me. The 2 coils are the same as 2 single coil pickups but the
> pole pieces from each coil reach down to make contact with opposite poles
> of the actual magnet, so one coil is in contact with the north pole while the
> other is in contact with the south pole. The magnet itself usually sits between
> the 2 coils (well it does in my DiMarzio, I've seen others where the magnet
> was thinner and 2 pieces of steel were used to extend the magnet's poles to
> underneath each coil). I'll try and draw a x-section:-
>
> Coil 1 Coil 2
> --------- --------
> | | | | | | | |
> | | | | | | | |
> ---| |--- ---| |---
> | |-------------| |<----pole pieces
> -| N S|-
> |pole Pole|
> | Magnet |
> -------------
I have never seen a pickup design like this. Of course, it should
work, but I think more common way to design a humbucking pickup
is to use two separate magnets that have reverse polarity. Of
course, the coils alsho have to have reverse winding.
If you want to make a pair of single coils to a (kinf od) hum-
bucker look if the pickups have a slab magnet underside of the
pickup (some have, others have the actual polepieces as magnets).
That slab is usually just glued to the bottom of the thing. Care-
fully remove the magnet and reglue it upside down. Then reverse
the connector wires.
I have done this to my Rick 4001 bass and it works just fine.
The humbucking effect is not as pronounced as with "real"
humbucking pickup, as the pu's are connected in parallel
(I'm planning to add a parallel/series switch) and the pu's
are physically apart. But it's noticeable.
-jPM
>
> Dave
> --
--
jP M{kel{ ({'s are a's with umlauts) jpmakela@cc.Helsinki.fi
---------------------------------------------------------------------------
From: dam@dcs.glasgow.ac.uk (David Morning)
Newsgroups: alt.guitar,rec.music.makers.guitar
Subject: Re: 2 Single Coils = Humbucker??
Date: 4 Apr 93 10:24:02 GMT
Organization: Glasgow University Computing Science Dept.
..and maybe I should finish this off for the guy who said he was confused
by the magnetic phase reversal.....
>>> Coil 1 Coil 2
>>> --------- --------
>>> | | | | | | | |
>>> | | | | | | | |
>>> ---| |--- ---| |---
>>> | |-------------| |<----pole pieces
>>> -| N S|-
>>> |pole Pole|
>>> | Magnet |
>>> -------------
This, as I pointed out is a stylised diagram, you don't seriously expect me
to produce a real one in ASCII??!
In the real world, the pole pieces are usually adjustable screws. The magnet
usually has two pole extenders fitted to the N and S poles to permit better
contact with the pieces themselves. The extenders are usually just plain steel
tapped with screw holes to allow the pole pices to screw into them.
OK...I'll try and draw a *real* humbucker end view in section:-
The sizes are still exagerrated a bit, the magnet and pole extenders are
usually much thinner than I've shown.
>>> Coil 1 Coil 2
>>> --------- --------
>>> | | | | | | | |
>>> | | | | | | | |
>>> ---| |--- ---| |---
>>> | | --------- | |<----pole pieces
>>> -| |---|N S|---|-|-
| | | | | Magnet | | | |<---Pole extender
-------------------------------------- Base plate
The base plate is usally made of some non-magnetic metal such as brass.
Magnetic flux travels from the North pole to the south pole (you all remember
your magnetic circuit theory don't you?? :-) )
Coils 1 and 2 are wound exactly the same way, no reverse winding or anything.
Magnetic flux travels from the magnet's North pole along the pole extender
and _UP_ through coil 1's pole piece. It then travels across to the top
of coil2's pole piece, _DOWN_ the pole piece and along the extender to the
south pole.
So the flux in coil 1 is travelling in the _opposite_ direction from that in
coil 2. Coil 1 is _UP_ and coil 2 is _DOWN_. Apply Fleming's thingumy hand
rule to get the direction of current flow in each coil and lo and behold,
they are opposite too, 180 degrees out of phase. Consequently any emf induced
in the two coils _by the common magnetic field_ (important!!) will also be
out of phase. This is the magnetic phase reversal.
If the signals from the two coils were simply added together, they would
cancel so, they are wired _out of phase_ to bring the phase relationship
between the voltage in coil 1 and that of coil 2 back into phase.
All right so far?
The hum cancellation effect comes from extraneous noise (ie hum etc) coupling
into each coil. This does _not_ come courtesy of the magnetic field but from
some outside source. Hence the voltages created in each coil by the ouside
source on each coil will be exactly the same and have the same phase
relationship. Summing these two voltages together in anti phase will cause
them to cancel, voila! hum gone.
Dave
From ftom@netcom.com Thu Feb 16 13:22:15 1995
Newsgroups: rec.music.makers.guitar,alt.guitar
Path: zip.eecs.umich.edu!newshost.marcam.com!usc!howland.reston.ans.net!ix.netcom.com!netcom.com!netcom14!ftom
From: ftom@netcom.com (Tom May)
Subject: Angled bridge pickup
Message-ID: <FTOM.95Feb15185457@netcom14.netcom.com>
Sender: ftom@netcom14.netcom.com
Organization: The Planet Eden
Date: Thu, 16 Feb 1995 02:54:56 GMT
Lines: 81
Xref: zip.eecs.umich.edu rec.music.makers.guitar:41797 alt.guitar:46749
I was looking through the stuff on http://www.eecs.umich.edu/~tjs/ and
found the following old article on pickups. I remember reading this
article whan it came out, and have believed it to this day, until just
now when I actually thought about it:
> Newsgroups: alt.guitar
> From: META000 <META@UNB.CA>
> Subject: Re: Bridge Pickup Alignment
> Organization: The University of New Brunswick
> Date: Sat, 28 Nov 1992 18:33:28 GMT
[...]
> As Don implied, the location of the polepieces along the vibrating
> part of the string determines (along with picking style, etc.) which
> harmonics will be more emphasized in the final output. If my
> physics knowledge serves me, higher harmonics have a SHORTER
> wavelength, while lower harmonics have a longer wavelength. That
> is, when a note is plucked, the string has numerous different
> vibrational patterns going concurrently, each covering a different
> proportion of the string's length, and, more or less, superimposed on
> each other (essentially high ones superimposed on low ones). The
> thinner and more flexible the string (although I gather there are
> some exceptions to this), the easier it is for the string to undergo
> little teensy bends in this place or that (i.e., short wavelength
> vibrations). So, all other things being equal, thinner gauge
> strings are "brighter" than heavier gauge strings, because they can
> vibrate at shorter wavelengths moreso than heavy gauge ones.
>
> So what the devil does this have to do with bridge pickups?
>
> Simple. For any two notes played, the same harmonic (e.g., the 5th
> harmonic) for each will have a different wavelength (assuming the
> two notes were different to start with), with lower notes having
> a longer wavelength for the same equivalent harmonic. What this
> means is that, for the SAME harmonic from any note played on the
> lower pitched strings, compared to any note played on higher pitched
> strings, you have to move further away from the bridge before you
> can pick up that vibration on the string at its' maximum displacement.
> Stated another way, the same harmonics on the high E as on the low E
> (remember, this is the same OVERTONE and not the same FREQUENCY) can
> be readily detected closer to the bridge.
>
> So, since the bridge pickup signal consists of a lot more harmonic
> content than the neck pickup, people like Leo Fender angled bridge
> pickups to provide a more CONSISTENT sound over strings, rather than
> provide some kind of special "hot-rodded" tone. The angling is a
> simple but effective way to make sure that the same overtones in the
> overtone series receive the same emphasis from string to string.
[...]
>Mark Hammer
Mark was usually right about things, but I think he's wrong here. The
point where a harmonic can be most readily picked up does not depend
on the string. No matter what the string, the fundamental has
its maximum displacement at half the distance from the bridge to the
nut, the first harmonic has its maximum displacement at 1/4 the
distance, the second harmonic at 1/6, the third at 1/8, etc.
This means a pickup which is *not* angled will detect the same
proportion of harmonics in all strings, and the Strat-style angled
pickup will be biased towards detecting lower harmonics on the lower
strings and upper harmonics on the higher strings, i.e., the upper
strings will sound brighter than the lower strings, instead of
sounding "consistent" like Mark asserted.
Mark seems to have gotten confused between the length of the sound
wave in air, which does decrease with increasing frequency, and the
length of the standing wave in the string, which depends only on the
string length and not the frequency of vibration. The standing waves
in the strings are what the pickup detects, not the sound waves in the
air.
Inasmuch as this article is sitting around in an archive that people
are encourages to check out, I just thought I would share my little
revelation.
--
Tom.