1. EMG active pup specs

hey folk

New to this forum and to winding, but I've been building instruments for myself for a few years. I see a few extended-range and multi-scale instruments coming down the pike in the next few years, so I'm starting to wade into this winding thing...slowly. I've read just about every post here, and I'm working on plans for a winder now.

My question: I know that active EMG pickups have some kind of buffer chip/circuit epoxied in with the magnet & coils to bring down the impedence. Has anyone here ever deconstructed one to see what's going on in there? What kind of chip/circuit they use for this?

Their spec sheets also hint at using low-gauss magnets...anyone know what's up with that? What's the idea behind it? Anyone ever measure one?

thanks for this great forum!

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2. Originally Posted by erikbojerik
hey folk

My question: I know that active EMG pickups have some kind of buffer chip/circuit epoxied in with the magnet & coils to bring down the impedence. Has anyone here ever deconstructed one to see what's going on in there? What kind of chip/circuit they use for this?

Their spec sheets also hint at using low-gauss magnets...anyone know what's up with that? What's the idea behind it? Anyone ever measure one?
I'm far less knowledgeable about this stuff than a lot of the folks here so take everything I say with a grain of salt, but I think I can answer your question, or at least confuse you further ; )

The function of a buffer, if I'm not mistaken, is to provide a high input impedance to the source (the pickup, in this case) and a low output impedance to the load (the cable & whatever the cable's plugged into) The reason for using a buffer makes sense if you meditate on ohm's law long enough to understand some of it's ramifications. More on this later, unless I get sidetracked.

Gauss is the unit of measure for the strength of a magnetic field, so a low gauss magnet is... you guessed it, a weak magnet. Why use a weak magnet? Well, the stronger the magnetic field is where the strings intercect it, the more it will affect the vibration of the strings. In other words, weak magnets don't suck heap big tone. I think this is often referred to as "magnetic drag" They (weak magnets) also don't produce as strong a magnetic field where the coil intercepts it, which makes for a lower amplitude signal in the coil.

This goes hand in hand with their low impedance coils, which presumably have relatively few windings, relatively thick wire, or (most likely) a combination of the two. This has the effect of (correct me someone, if I'm wrong here) creating a coil with lower inductance and capacitance, which decreases AC impedance, broadening the frequency response in both the bass and treble directions. It also makes for fewer winding to intercept our (low gauss) magnetic field which makes for... you guess it, a lower amplitude signal in the coil.

Combine these effects and you get a pickup that has very little effect on the strings, a super wide (crisp sounding with powerful lows) frequency response, but jack squat for output level (with diminished ability to drive an instrument cable and subsequent amplifier stage.)

(is it the Heisenberg uncertainty principle that implies that you cannot measure anything without affecting it? These kinds of pickups try to interfere with the strings as little as possible - to have the smallest possible "observer footprint" note: some (many) people like the "warm" vintage sound - less highs, more mids, but if you're Kirk Hammett... bring on the wide band)

Oh, yeah... low output level...

What to do, what to do?

Oh, yeah, buffers.
Don't pay any attention to what I'm about to say - I really don't know what I'm talking about.
The buffer, in this case, is a way to protect the sensitive operation of the pickup from the great unknown of whatever it is you plug into your jack. If they didn't buffer the pickup and you plugged it into a 50' unshielded cable that went to a fuzz face, the results would not be pretty, ruining all their hard work. Placing a buffering circuit in there gives the pickup a consistent, known load that their engineers can count on when coming up with really sensitive, low impact pickups.
So: my guess is that they use a buffering scheme to reduce loading on the pickups (to preserve that extra tone they worked so hard to design into them) and possibly (probably?)apply gain to get the singal level up to standard pickup levels. They may or may not combine these in one stage...
A jfet (junction field effect transistor)in common source mode with a bit of gain and plenty of NFB would, if I'm not mistaken (but I usually am ; ) provide a nice high input impedance and enough gain, along with a low enough output impedance to achieve their goals
They might use an op amp
They probably use an op amp
Hopefully they use a *good* op amp but an ad797 is too much to hope for. I'd settle for an ne5532
Or they might use a BJT (bipolar junction transistor) as an emitter follower(re: buffer stage), followed by one hooked up in common emmiter (re: gain stage), follwed by *another* emitter follower... (this is unlikely)
The list goes on... a darlignton pair, a single BJT in common source...
Depending on the exact specs of their pickup and exactly what they wanted to achieve, they would design an appropriate buffering circuit.

In other words, I have NO idea what is in that buffer circuit, but I know what it's there for, and it's probably *really simple*

Now I'm just TOTALLY rambling... trying to puzzle this stuff out myself as I explain it.

Honestly, just wait for David Schwab to come along and correct me - he actually knows what he's talking about. And check out his web site - he makes pickups that imho are voiced better than EMGs (you can listen to sound samples)

Hope I created more questions for you than I answered ; )
(that's when you know you're learning and thinking)

Michael Miller

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3. As to what preamp chip they're using, we know it's going to be reasonably low noise and low current draw and it's going to cost not more than a dime or two. My guess is 062, 072 or 082 series. They probably change up every 10 years or so. Current noise specs are 96dB on their best humbuckers and have been for quite a while. Audiophiles they are not.

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4. Not being an electrical engineer, I don't quite understand how all that results in a broader frequency response, but I'll buy that. It seems to be one of the defining features of EMGs.

Aside from that, I follow the logic up to the "low output" part of the discussion. I guess the buffer also works as an amplifier...?? But how exactly do you think they can boost the output without also boosting the noise? EMGs have a rep for being low-noise....

David, I think you have a sign error there...the noise specs on a 89 (tri-coil) are MINUS 90s....-94dB for the single coil, -99dB for the humbucker. Those seem like pretty good noise figures to me, but I'm very new to this, so bear with me if I'm off base...

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5. Originally Posted by erikbojerik
Not being an electrical engineer, I don't quite understand how all that results in a broader frequency response, but I'll buy that. It seems to be one of the defining features of EMGs.

Aside from that, I follow the logic up to the "low output" part of the discussion. I guess the buffer also works as an amplifier...?? But how exactly do you think they can boost the output without also boosting the noise? EMGs have a rep for being low-noise....
The trick is to use a low-output coil (fewer turns, so lower inductance and higher resonant frequency) and use the buffer amplifier to raise the output to the typical range for passive pickups having five or ten times as many turns on the coils. Such coils are quite flat in the audio range, so all tone shaping is done by filter components built into the buffer amp. The EMG website actually explains this, but not very clearly.

Part of the low output is due to use of small magnets with little string pull, reducing wolf tones.

David, I think you have a sign error there...the noise specs on a 89 (tri-coil) are MINUS 90s....-94dB for the single coil, -99dB for the humbucker. Those seem like pretty good noise figures to me, but I'm very new to this, so bear with me if I'm off base...
It's true that these are minus, but in common usage this is understood but not stated.

In guitar service, having noise 90 db down means that the pickup is noiseless in practice. Only in a dead quiet recording studio would there be even a chance to detect the noise in such a device.

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6. I tried to comment to this the other day but the forum was not responding...

EMG uses an op amp of some kind ... it has their name on it, so I guess it's something made for them.

I was always under the impression that they used low impedance (low output) coils, but it seems they actually use pretty normal high impedance coils.

Their magnets aren't any smaller than normal, at least for the 81. The EMG-40DC I have home has as much pull as the pickups I'm making with normal sized ceramic magnets, maybe even more.

I'm basing all this on some photos someone send me once. They dissected a non working 81 to see what was inside. Looks like a fairly normal humbucker with a alnico magnet, twin blades, and a bunch of wire on the bobbins. The coils were wax potted before the pickup was encapsulated. The preamp was on the baseplate, which was made from a PCB.

The one thing about EMG's is they use a differential input to the buffer and run each coil separately. They also use the buffer to mismatch the response of the coils, and probably some EQ also. They call this "tone modeling".

I used to think they were pretty hi-fi bass pickups until I started making my own. They do have a very consistent tone though. If you like their sound, you always get it. You don't get much else though.

(as a disclaimer I'd like to point out that I have no interest in copying EMG, and merely found the photos to be interesting from a "oh that's what's in there" basis.)

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7. Originally Posted by erikbojerik
Not being an electrical engineer, I don't quite understand how all that results in a broader frequency response, but I'll buy that. It seems to be one of the defining features of EMGs.
The more turns of wire you use, the louder the pickup, but also the higher the inductance.. after a while you start to lose high end, and low end too. The coil starts to behave like a band pass filter.

Let's use Alembic as an example. I think we can all agree they make very wide response pickups. They use about 1500 turns of 40 gauge wire wound right on a ceramic magnet. They have a matching dummy coil with no core.

These pickups have very little output, but very wide frequency response. You just boost up the level to normal high impedance levels, and you have very clean and clear sound.

EMG's don't really have that wide a response. They are about what you get with a buffered high impedance pickup (which is what they are).

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8. Originally Posted by erikbojerik
Not being an electrical engineer, I don't quite understand how all that results in a broader frequency response, but I'll buy that. It seems to be one of the defining features of EMGs.
I'm not an Electrical Engineer either, but if you want to know about the principles that give any pickup its frequency response, I'll give it a better whack:

There is one thing that determines a pickup's frequency response: Impedance. That one thing is determined by 3 things: DC resistance, inductance, and capacitance. DC resistance is a property of the wire in the coil - its material and thickness, Inductance is a property of the coil itself, and capacitance in this case is known as "parasitic" capacitance - in an "Assume the Cow is Spherical" world, it would not be there, but in the real world it is. All those turns of wire with insulator between them form a capacitor, whether we like it or not, and one end of this capacitor is connected to ground, because one end of the coil is connected to ground Your coil is an inductor AND it is also a capacitor connected across itself.
Bear with me, this will all make sense. (I hope)

Inductors impede AC - we say they have "AC impedance" and this impedance increases with frequency.

Inductor = resists treble / admits lows

Capacitive circuits have infinite DC resistance (which is why we use them to block DC between amplifier stages) but their impedance DECREASES with frequency, allowing signal to pass through. The higher the capacitance, the more easily it passes lows.

Capacitance = resists bass / admits highs

BUT remember, this parasitic capacitance is actually connecting our signal to ground, so the inductance resists highs and the capacitance allows the highs to go down the drain, so they work together.

Now these two combined effects only mean something (meaning you can only do the math) when there's a DC resistance involved. If a coil has a lot of DC resistance, it becomes far, far, easier for treble to go down the drain
If a coil has fairly little DC resistance, not as much of it takes the easy road down the drain, because there's an easy road to the amp, too.

Put these things together and you discover that the less inductance, the less capacitance, and the less DC resistance your coil has, the flatter its frequency response will be.

Does that make sense? Sorry, I was going to explain better in my last post, but I ran out of steam, I guess

I guess the buffer also works as an amplifier...?? But how exactly do you think they can boost the output without also boosting the noise? EMGs have a rep for being low-noise....
Yes, I'm sure the buffer is also an amplifier and they can't boost the output without boosting the noise. Another benefit of low impedance pickups is that they are naturally, inherently, lower noise devices than high impedance pickups. They also pick up 60hz buzz just as weakly as they pick up guitar strings so if you hook them up to an op amp and do a little filtering with negative feedback, you get a nicely sized signal and not much noise. If you boost jack squat for noise by 10 times, you still have jack squat for noise

Schwab: you posted while I was posting so I may be proven wrong on some points before I even posted
lol
Great info - thanks. I was thinking of buffering my pups and I wasn't sure what it would do - now I have a better idea Great pics, too

Also:
Joe - this is the second time I've heard the term "Wolf tone" to describe something other than the most deformed 5th in Just temperment.
Obviously they're different things... but I don't understand the mechanism of the wolf tone you're referring to... is it a sharpening of the fundamental due to magnetic pull? Does it alter the harmonics of the string... effectively creating a magnetic bessel curve by tightening the string only along a certain portion of its length? Wow... this is reminding me of work I've done with Shakuhachi bore shaping... (japanese end blown flute)

I think I just answered my question

Michael Miller

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9. Wolf tones

A wolf tone is defined as an interval in a scale that's noticeably out of tune because of the limitations of the scale in use.

"Stratitis" is another term for the discordance created when a guitar pickup magnet is adjusted too close to the string and particularly afects the thicker more magnetic strings when played up the neck.

Imagine the magnet(s) creating an floating anchor point part way along the string, strength varying as the string vibrates... then look at the patterns you can get with a harmonograph.

Better still, try it on your guitar.

S.

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10. Just saw the "Joe" part,

Apologies Joe, need new glasses.

S.

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11. Thanks guys, and thanks also for the photos David.

I imagine there's more on that circuit board than just an op amp, eh? Any SMDs floating around on there that you know of?

Would this buffer/amp circuit be similar in principal to a typical on-board active preamp?

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12. I imagine there's more on that circuit board than just an op amp, eh? Any SMDs floating around on there that you know of?[/QUOTE]

Yes, you can see the SMD's in the last photo. I'm actually surprised the op amp isn't one.

Originally Posted by erikbojerik
Would this buffer/amp circuit be similar in principal to a typical on-board active preamp?
Yeah, more-or-less. As I said they claim to do tone shaping and noise reduction at the preamp.

You don't need all that though. Look up some JFET or op amp buffers online. There are a bunch. Wind a low output pickup and use a buffer.

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13. Hey DS, don't forget you can still have low impedance with a full coil of wire. Look close at the wire, it looks pretty hefty to me. Maybe 38 AWG, that would make a very low impedance coil I would think.

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14. Never mind, I think I mis-read the post.

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Hey DS, don't forget you can still have low impedance with a full coil of wire. Look close at the wire, it looks pretty hefty to me. Maybe 38 AWG, that would make a very low impedance coil I would think.
Yeah, it looks a little heavy, but I think it's the wax. Larger diameter does give lower resistance.

This is what the guy wrote. He's from Poland so his English was a bit spotty. I forgot he wrote specs... What would .06 mm be in AWG?

EMG81

Magnet: Ceramic (cuting) 56x3x13mm
Wire: 0,06mm (PE)
Core: 54x3x12,5mm (silicon steel?), solid steel.
Coil: 4,18KOhm (one coil), wax potted, aprox. 5500-6000 turns, h=7,5mm
Bobbin: 64x13x9mm (or with "tube legs" 12,2mm)

Coils conection:

-opamp--------^^^^^^^^---------^^^^^^^^^^---------opamp+
ground

IC unknown, marked as EMG001
Here's another view.

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16. Originally Posted by David Schwab
Yeah, it looks a little heavy, but I think it's the wax. Larger diameter does give lower resistance.

This is what the guy wrote. He's from Poland so his English was a bit spotty. I forgot he wrote specs... What would .06 mm be in AWG?
0.0635mm or there abouts is 42 AWG. So, if you take account of the tolerance (lets say -5%) it's roughly 0.06mm (0.06033mm).

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17. Originally Posted by mjmiller
Joe - this is the second time I've heard the term "Wolf tone" to describe something other than the most deformed 5th in Just temperment.

Obviously they're different things... but I don't understand the mechanism of the wolf tone you're referring to... is it a sharpening of the fundamental due to magnetic pull? Does it alter the harmonics of the string... effectively creating a magnetic bessel curve by tightening the string only along a certain portion of its length? Wow... this is reminding me of work I've done with Shakuhachi bore shaping... (japanese end blown flute)
The extra pull, especially if nonlinear, moves the harmonics into increasingly non-harmonic frequency relationships. The ear is very sensitive to this. There are a number of names for various kinds and perhaps degrees of this: wolf tones and stratitis come to mind.

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18. Originally Posted by David Schwab
This is what the guy wrote. He's from Poland so his English was a bit spotty. I forgot he wrote specs... What would .06 mm be in AWG?
It's #42, as mkat reported. Having a buffer right next to the coil eliminates the capacitance of the cable from guitar to amp, and will raise the resonant frequency to something exceeding 7,000 Hz. This would have the effect of making the response quite flat for guitars. As would winding 5,000 turns versus 10,000 turns, as inductance varies as the square of turns count.

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19. Right - I used to make end blown flutes from bamboo, and there are a couple of techniques I used to alter the bore profile in different ways. slipping a beveled choke into the barrel is equivalent to this pull for the neck and mid pickups and tapering the bore at the embouchure end is the equivalent of the bridge pickup. This is necessary to bring the second register into tune - with a straight bore, it's naturally a tad flat. I experimented extensively with bore shaping (I'll spare you the details) and I can confirm that it has a huge effect on tone. I realized a lot more connections after having posted that... I do that a lot - I post about something, and the process of writing my thoughts gets me thinking more, and more clearly, and then I realize that I'm totally wrong about something I said, or I asnwer my own question, or something totaly different. Damn brain...
I like the term stratitis - is that from strat players who move their pickups too close to the strings? I used to be guilty of that, but now the pups are way down near the pickguard - I find I prefer the tone (I play cleanly a lot more these days)

Great freakin thread, guys. Tons of cool info - food for thought - and it's cleared up a number of misconceptions I had

Michael Miller

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20. Originally Posted by David Schwab
Yes, you can see the SMD's in the last photo. I'm actually surprised the op amp isn't one.
Ah, right you are. Ditto my initial reaction upon seeing the op amp...which your guy in Poland could probably ID by cutting through what looks like a bit of a rubber coating.

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21. Originally Posted by erikbojerik
Ah, right you are. Ditto my initial reaction upon seeing the op amp...which your guy in Poland could probably ID by cutting through what looks like a bit of a rubber coating.
I don't think it has a rubber coating... it just looks funny from having been in epoxy.

I see they use a LF442 dual low power JFET input op amp for their tone control circuits. I'd bet the IC in the pickup is similar.

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22. Originally Posted by David Schwab
Looks like a fairly normal humbucker with a alnico magnet, twin blades, and a bunch of wire on the bobbins.

The one thing about EMG's is they use a differential input to the buffer and run each coil separately. They also use the buffer to mismatch the response of the coils, and probably some EQ also.

1) Are you sure its alnico? Everyone says 81's have ceramics, while the 85's have alnico.

2) If I'm understanding this right, are you saying that 81's are actually wired in parallel instead of in series like a standard humbucker? I guess that would make sense if they're aiming for more clarity, and parallel is lower output than series but with their preamp they don't need to worry about that.

Also, do you think the coils might have a differing number of windings, like a Seymour Duncan Pearly Gates? Even if the EMG doesn't, I guess they're doing a similar thing through the electronics anyway.

EDIT: whoops, what an embarrassing mistake to make on a first post. I didn't notice there was a second page to the thread. So I guess it is indeed ceramic, and by that wiring diagram (op- ^^^^^^ ^^^^^^ op+) looks like it is in series instead of parallel.

So much for my Sherlock ambitions...

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23. Originally Posted by sumitagarwal

1) Are you sure its alnico? Everyone says 81's have ceramics, while the 85's have alnico.
I was going by what was written in the description that came with the photos. EMG says it's a ceramic magnet.

The EMG-81 has the familiar U-shaped humbucking structure but replaces the pole pieces with steel bars and a smaller ceramic magnet.
Originally Posted by sumitagarwal
2) If I'm understanding this right, are you saying that 81's are actually wired in parallel instead of in series like a standard humbucker? I guess that would make sense if they're aiming for more clarity, and parallel is lower output than series but with their preamp they don't need to worry about that.
It's not wired in series, but it's not really parallel either. It's wired in a differential mode. So it's like just one coil, as far as the impedance. The output of the two coils is summed together, but they do not interact the way passive parallel coils do, so the DC resistance is not halved.

The common connection of the coils goes to ground, and the hot connection of each goes to the (+) and (-) inputs of the op amp.

Originally Posted by sumitagarwal
Also, do you think the coils might have a differing number of windings, like a Seymour Duncan Pearly Gates? Even if the EMG doesn't, I guess they're doing a similar thing through the electronics anyway.
I have no idea. They might though, because they said the 58 was too noisy, so they changed it and it became the 85. The 58 was a really nice pickup.

Originally Posted by sumitagarwal
So I guess it is indeed ceramic, and by that wiring diagram (op- ^^^^^^ ^^^^^^ op+) looks like it is in series instead of parallel.
It looks that way because the ASCII graphic became misformatted. The connection between the two coils is grounded.

Here's some more interesting "I wonder what's in there" pictures...

Notice the brass screen for shielding. I guess that would make that a Faraday Cage. That's a boatload of wire on those coils! They seem to wind all their bobbins until full. The larger the coil, the more wire they wind on it.

It's fun taking things apart!

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24. Awesome post, man. Seriously interesting stuff here and good clarifications.

I guess EMG is sort of like two single-coils being used simultaneously... almost as if you took output from each coil and ran them separately to two identical amps. Really weird, and really cool. Nothing like it (or even possible?!) in the passive world. I wonder how they wire their "81 in a passive box" EMG H4. Not that I've heard it.

Thanks for replying to such an old and dead thread. Built-in Faraday cage? Great idea! I'm having more respect for EMG than before.

I've created a 'Partscaster' hot-rodded baritone Tele and I'm thinking about EMG's Telecaster actives. On their website they even say something like "undoubtedly the best pickup EMG makes"!

And thanks for replying (in such detail!) to such an old thread. You're the man!

P.S. Anybody else surprised that EMG doesn't try to make a 81/85 in single-coil size? I'm sure Strat and Tele players would eat that up, and that ESP players would try to stick two of them in their humbucker slot! I guess it would be pretty tough trying to stick all those windings into so little space...

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25. Originally Posted by sumitagarwal
Awesome post, man. Seriously interesting stuff here and good clarifications.

I guess EMG is sort of like two single-coils being used simultaneously... almost as if you took output from each coil and ran them separately to two identical amps. Really weird, and really cool. Nothing like it (or even possible?!) in the passive world. I wonder how they wire their "81 in a passive box" EMG H4. Not that I've heard it.
Any time you mix two pickups passively you have one loading down the other. Even if you buffer the output. The way around that is to buffer each pickup first, and then mix them together.

I think the passive pickups are wired up like regular passive pickups... they have 4 conductor wiring and all. I haven't heard any good reviews on them. I suspect they are taking the same parts as the actives and just leaving out the preamp.

Originally Posted by sumitagarwal
Built-in Faraday cage? Great idea! I'm having more respect for EMG than before.
Alembic do the same thing, only they use braided copper mesh, like you find on coaxial audio cables.

Originally Posted by sumitagarwal
I've created a 'Partscaster' hot-rodded baritone Tele and I'm thinking about EMG's Telecaster actives. On their website they even say something like "undoubtedly the best pickup EMG makes"!
That's just the Tele neck pickup... that's the one they think is their best pickup. I think it's very odd to not be able to make them all sound the same. As I pointed out, they wind more wire on larger coil forms, so their 6 string bass pickup has a higher DC resistance than the 4 string pickup, and each one has a different resonant peak. I think that's dumb myself.

The rhythm pickup (EMG-FT) is undoubtedly the best pickup we make. All the elements are in the right proportion; magnet choice, coil size, amount of turns, and good luck have given the EMG-FT the sweetest sound of any EMG.
They made some custom strat pickups for a guitarist who's name escapes me at the moment, with tele neck pickups in the strat size case.

Originally Posted by sumitagarwal
And thanks for replying (in such detail!) to such an old thread. You're the man!
I'm interested on how things work... that's how I started fixing guitars... because I take everything apart, and then have to figure out how to put it back together!

Seymour Duncan used to unwind pickups to learn how they are wound. I'm not looking to copy EMG pickups, but I'm curious to know what's in them. Someone else took the 81 apart, and I had an old SA sitting around for a while in my pickup box that I wasn't using. It was cosmetically disfigured, so I figured what the heck! I was hoping to keep the coils intact, but that's very hard to do.

Originally Posted by sumitagarwal
P.S. Anybody else surprised that EMG doesn't try to make a 81/85 in single-coil size? I'm sure Strat and Tele players would eat that up, and that ESP players would try to stick two of them in their humbucker slot! I guess it would be pretty tough trying to stick all those windings into so little space...
They are slow to come out with new models. They just came out with a P-90 size pickup not too long ago.

There are a lot of single coil size humbuckers on he market already... but they are all passive.

I think the one disadvantage of the differential wiring is some of the pickups, like the P bass replacement, sound too thin. Series wiring gives a nice fat bottom.

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26. Nice to find people with a real passion for this stuff... let me know when you open up mass production! I'll be watchin for ya.

I'm trying to wrap my head around what would be the closest passive equivalent to the EMG active humbucker wiring... maybe it would be hotly overwound dual coils wired in parallel? Still quite different, but maybe.

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27. In a related question, about parallel/series/differential wiring: does anyone happen to know how hum-canceling 'single coil stacks' are wired? I have the Seymour Duncan Vintage Stacks and I'm wondering if they get the humbucking by added a bottom coil in parallel or in series.

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28. Originally Posted by sumitagarwal
In a related question, about parallel/series/differential wiring: does anyone happen to know how hum-canceling 'single coil stacks' are wired? I have the Seymour Duncan Vintage Stacks and I'm wondering if they get the humbucking by added a bottom coil in parallel or in series.
I'm pretty sure they are in series. You can only do series or parallel with passive pickups. The differential thing is part of the op amp's wiring.

The older Duncan stacks are covered by this patent from 1985: 4524667

Now they state they have a "new patent applied for design", so they might have changed things. Kevin Beller, Duncan's chief designer got this patent in 2007: 7166793, which might be the same pickup. It's an advancement on the DiMarzio/Kinman style stack with magnet shields and added loads in the bottom coil.

I used to have some Duncan stacks, and I thought they sounded pretty good. I've installed a few DiMarzio Virtual Vintage Pro stacks lately... they have alnico II magnets and are supposed to sound like p-90's. They sound very good. It seems this is the direction to go in with stacked pickups.

The EMG SA seems to have an alnico bar magnet running though both coils, which is similar to the original Duncan patent. I haven't gotten to the bottom coil yet, so I don't know what's in there.

I made a Tele lead stack with a steel blade running through both coils, and two magnets on the bottom of the blade like a P-90. Even though I would it pretty hot, it's very bright. This must be why some stacks have a lot of wire on them, to try and warm them up. But the real issue is phase cancelation. My pickup gets a good vintage Tele tone, but that wasn't what I was going for!

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29. Really cool insights... I'm interested in talking about the EMG SA's more, and also about maybe the (discontinued?) EMG-S4 passives.

But first about the Dimarzio and Duncan stacks: I'm really interested in the Dimarzio Virtual Hot T (seems to match some specs on my beloved Duncan Alnico II Humbucker well, the A2 magnet and the T/M/B ratings). How would you compare your experience between the Duncan and Dimarzio stacks? I find the Duncan Vintage Stack really interesting, but a bit harsh for my tastes. I've noticed all my favorite pickups in my other guitars are Alnico II or III.

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30. Hi David S
i know this is an old thread but did you ever discover if the alnico magnet went right through the two coils of the SA you disected?
I wound some stacked coil pickups way back in the late 70s (inspired by Seymour Duncan's stacks) with the two coils in series using AWG 44 plain enamel and approximately 8000 turns on each coil which I then connected in series out of phase. I found them to be a bit thin sounding due to the bass cancellation caused by inductive coupling of the two out of phase coils.
The Kinman, Belcher and Stich designs appear to have addressed this bass rolloff but the EMG SA appears to be the same construction as my early stacked coil pickups. Perhaps the differential preamp design has some built in bass compensation?? Do you have any further details on the SA preamp design - component values etc?? ( I have seen the EMG 81 preamp design)
Or do EMG SA pickups sound a bit thin on the bottom end as well??
Cheers and thanks for the info - I only discovered this forum recently!
bajaman

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31. Yes, the SA has the magnet running through both coils like the old Duncan/Dimarzio designs. I've made a few of those and they are very bright sounding pickups. This is probably why they are always wound hot.

The EMG design doesn't run the coils in series, but instead has each one connected to one of the inputs on the op amp.

Here's the schematic for an 81. I guess it's the same one you have? I didn't make this so I can't verify it. It was traced from an actual circuit board. I'd imagine the SA is similar. Also a photo of the inside of an SA.

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32. Hi David
Thanks - i do already have that EMG81 schematic and I have a set of EMG S type pickups (ceramic) on a squier strat. I don't like the sound of them much though - they may be noiseless but they sound very flat - not a lot of fullness in the bottom end and actually quite muted in the top end - no sparkle (probably too high an inductance?).
Another thing I found disappointing was the absence of any real "quack" when using the neck and middle (or bridge and middle) pickups together!
I have not tried the Kinmans or Stich (Fender Noiseless) pickups, but their design promises to be an improvement on the EMG design - particularly the lack of inductive coil coupling between the top and bottom coils. Do you have any experience with these pickups? If so, what are your thoughts, feelings about them etc.
I am going to sell off these EMG S pickups - they do not deliver the tone I desire from them. I was contemplating winding some stacks with Humbucker bobbins and using short Neo rods for the top coil and unmagnetized steel slugs for the bottom coil, separated by a downward facing U shape channel of silicon steel (old transformer lamination piece) to conduct the magnetic field away from the bottom coil. Maybe I do not need any slugs in the bottom coil??
I was going to use the LM4250 differential preamp like the EMG 81 schematic (but modified slightly).
I will post some pictures when and if they work out and give me "that" strat sound that the EMG S pickups do not!!
cheers
Steve

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33. I've never used the S pickups. I had a set of SAs in a guitar, and they don't sound bad. They lack a certain sparkle in the top end, but otherwise are very Straty. I don't use EMGs in any of my instruments anymore.

My Teleish guitar I made has some old lawrence L-250 sidewinders that sound nice, though they used to sound better in my Fender Mustang.

I have installed Dimarzio Virtual Vintage Pro pickups in a few guitars from the same customer, and they sound very good. They really sound like single coils.

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34. "They lack a certain sparkle in the top end"
This is exactly how the S pickups sound to my ears too.
Too much inductance methinks
bajaman

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