EMG active pickups preamp circiut schematic. [Archive]

Joe Gwinn

09-08-2008, 02:57 AM

The circuit diagram does not match the circuit of the pictured circuit board.

Are the two pickup coils identical?

If yes, the circuit diagram isn't quite right, but is probably close. I would expect a balanced differential amplifier merged with a DC voltage divider to set the DC operating point (~ground) at about one half the battery voltage, allowing operation off a single 9 volt battery.

If no, the circuit still doesn't quite make sense because the gain of the plus channel will depend too much on the AC resistance of that coil. One would expect a series resistor like the 30 Kohm resistor in the minus path.

RedHouse

09-08-2008, 06:39 AM

I wonder if the schem is correct about it being a LM4250

Checking the data sheet it seems that low power is the only thing a LM4250 has going on, it's a general purpose OpAmp.
(not a low noise job)

It's a shame whoever took that pic of the PCB didn't flip it over and give us a look at the other side, might be more SMT over there.

David Schwab

09-08-2008, 07:40 AM

I know where this schematic came from, and it's the same source that sent me pictures of the inside of an EMG 81 (see below). I got the photos over two years ago, and schematic this past July.

Yes, this is supposed to be accurate. I haven't traced it from the photos I have though, but the same people did both (see below). It took them a while to trace the PCB from inside the pickup. The only thing they didn't know was the exact op amp, since it had no number on it, besides a private EMG part number.

The other circuit from the booster switch board is different. That photo is not where this schematic came from. Here's the board attached.

I'd guess the unbalanced coils are part of the tone modeling thing they do. One of their older pickups, the EMG-58 was too noisy (hummed too much), so they redesigned it as the EMG-85 which is quieter. They also have very fine brass screening acting as a Faraday cage for shielding.

The source that did the schematic said the coils were matched, but I think that's hard to say since they had to destroy the pickups to find out.

But the specs were listed as follows:

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

IC unknown, marked as EMG001

Electric shematic will be able in a few days.

salvarsan

09-08-2008, 04:56 PM

National Semiconductor's datasheet examples suggest
that EMG started with component values from NS'
gain-of-5 differential amp schematic, and set the current
bias to ~1 microamp to optimize the noise power figure.

A 10k output buffer resistor is also prominent throughtout
the datasheet specifications.

That lack of a 30k resistor on the non-inverting pin
looks like an error instead of a design decision.

LM4250 datasheet:
http://www.national.com/ds/LM/LM4250.pdf

-drh

Mike Sulzer

09-08-2008, 11:14 PM

David Schwab

09-09-2008, 12:45 AM

This circuit is certainly not balanced: inv, gain = 5, non-inv gain = 6. So, yes, maybe a resistor in series with the non-inv input has been left out. It would have to have a value of 13.7K to lower 6 to 5. (The lower leg of the voltage divider is the two 137K resistors in parallel.)

I don't know if there is a part left out, but it's common for people to wind unbalanced pickups... maybe they wind balanced coils and unbalance them electronically?

The inv. input input impedance is 30K; this is kind of low for a high impedance coil. And the input impedance the other coil sees is 68.5K. This does not make sense.

From the EMG site (italics added)

http://www.emginc.com/company.asp

Tone Modeling

One of the most important aspects governing the tone of a pickup is the resonant frequency. EMG Pickups use "Impedance Modeling" to manipulate the two coils. This innovation allows us to shape a mix of the reactive slope and resonance from each of the two coils. The idea is to achieve a complex mixture of each coils phase and frequency response resulting in a richer tone from the pickup. This means the sound is vibrantly alive with more harmonics than from conventional passive pickups. EMG Pickups like the EMG-S, EMG-SA, and the EMG-60 use this technique to its fullest, while the EMG-81 uses modeling in only a small way. Modeling might work well for a single coil pickup, but not for a design such as the EMG-ACS Acoustic Sound Hole Pickup. As each pickup design is approached differently, it all depends on the final result we're searching for.

Also remember that the two coils are not wired in series, so loading it down like that will make it darker sounding.

Mike Sulzer

09-09-2008, 01:44 AM

A 6/5 gain ratio at low frequencies will not do a good job of canceling the hum from magnetic fields. EMGs do cancel hum well, and so I think something is missing. Perhaps the coils are different as someone mentioned.

It is true that actively adding the outputs of two different resonant circuits can produce responses that cannot be achieved with two identical resonant circuits. If the two coils are the same, they would have the same resonant frequency, but different Qs. If the coils are different, both parameters could be different.

The differences that can be achieved with such an active circuit are greater than can be achieved by putting the two different coils in series. If the cable capacitance dominates over the inter-winding capacitance, as it can, then the two inductors pretty much just add in series.

David Schwab

09-09-2008, 07:19 AM

I think every EMG made has the coils in parallel. That's one thing I don't like about the EMG-P.

I have an old Bartolini Hi-A pickup with one coil being intentionally 1K different from the other, and it's dead quiet. I had it installed in one of my '74 Ric basses, and along with total copper foil shielding of the bass, I was able to remove the string ground with no noise whatsoever.

I make some bass pickups with similarly large offsets with no hum problems.

EMG's have the entire pickup in a Faraday cage made from very fine brass screen. As I mentioned, some EMG models that had very mismatched coil circuits and did indeed hum. The EMG-58 was one of those. We used to use them in the American Showster AS-57 tailfin guitars, and they were the best sounding EMG humbucker, but they were a tad noisy. They replaced them with the 85, which is quieter, but lacks the harmonics of its predecessor.

Either way, take a look at the photo I posted of the circuit board inside the 81. That's where that schematic came from. The IC and one surface mount part is missing, but you could probably trace the circuit assuming they didn't use a double sided board. I've been meaning to do it but haven't had the time.

Here's an EMG SA, which is also very mismatched:

Mike Sulzer

09-09-2008, 05:00 PM

Sure, you can use different numbers of turns on the two coils. Cancellation of magnetic hum using two coils requires that the two coils have the same overall sensitivity. Since the sensitivity depends on both the number of turns and the magnetic core, you can get good cancellation with different number of turns if the cores are different in a complementary way. Simply making the number of turns different with two identical cores decreases the degree of cancellation. This is how it is in theory and how it works in practice. It might still appear to be good enough most of the time, but in an environment with really high stray magnetic fields, you need really good cancellation.

Shielding with a conducting material is for electric fields. Both kinds of hum are a problem, and each has a different solution.

Dave Kerr

09-09-2008, 05:37 PM

EMG's have the entire pickup in a Faraday cage made from very fine brass screen. ...
Here's an EMG SA, which is also very mismatched:

I'm curious about how the cage is wired - is that (and any other metal) connected to a drain wire or braided shield that's sent to ground, separate from the beginning and end of the coils?

ubaid88

09-09-2008, 05:59 PM

So is anyone who wants to make clone of them.

Mike Sulzer

09-09-2008, 08:05 PM

So is anyone who wants to make clone of them.

No way. This is not a circuit I would use when you have both coils available separately. You can put an op amp, non-inverting, on each coil and add the outputs through resistors. If the coils are the same, you can make the amplifier inputs truly identical, adjusting the input resistance and capacitance for the sound you want. If you want to use different coils, you have the most flexibility in adjusting the input impedance and gain to get the sound and good hum cancellation.

ubaid88

09-09-2008, 08:23 PM

No way. This is not a circuit I would use when you have both coils available separately. You can put an op amp, non-inverting, on each coil and add the outputs through resistors. If the coils are the same, you can make the amplifier inputs truly identical, adjusting the input resistance and capacitance for the sound you want. If you want to use different coils, you have the most flexibility in adjusting the input impedance and gain to get the sound and good hum cancellation.

I just need clean sound. I heard one of the Emgs it was as clean as acoustic guitar with high gain.

David Schwab

09-09-2008, 09:06 PM

I just need clean sound. I heard one of the Emgs it was as clean as acoustic guitar with high gain.

EMG's are not hi-fi clean. They sound like regular pickups with a buffer.

If you want clean wind a low impedance coil and use a preamp to boost the level up. Just wind a regular humbucker with about 1000 turns on each coil. That will be as clean as an acoustic guitar.

David Schwab

09-09-2008, 09:12 PM

I'm curious about how the cage is wired - is that (and any other metal) connected to a drain wire or braided shield that's sent to ground, separate from the beginning and end of the coils?

As far as I could tell is was grounded at the same spot as the coils were, which is the common ground.

It totally enclosed the pickup.

David Schwab

09-09-2008, 09:16 PM

So is anyone who wants to make clone of them.

Not me. I was just curious how they had their coils arranged. I like my pickups better. :D

Joe Gwinn

09-10-2008, 03:40 PM

I think every EMG made has the coils in parallel. That's one thing I don't like about the EMG-P.In the circuit diagram, the coils are not in parallel. They are each connected to their own input of a differential amplifier, and so are electrically isolated from one another. Unlike a direct-wired electrical parallel connection, the coils do not load one another.

I have an old Bartolini Hi-A pickup with one coil being intentionally 1K different from the other, and it's dead quiet. I had it installed in one of my '74 Ric basses, and along with total copper foil shielding of the bass, I was able to remove the string ground with no noise whatsoever.

I make some bass pickups with similarly large offsets with no hum problems.Perfect matching is not required to obtain adequate hum cancellation. Here is a simple numerical example:

Consider each coil as two voltage sources in series, the music source (Vm) and the hum source (Vh). The coils also differ in that they don't have the same number of turns and thus induced voltages, the ratio being called k, where k=1 if the coils are identical. All of k will be allocated to coil 2. The coils differ in that the algebraic signs of Vm and Vh are the same in coil 1, and opposite in coil 2, so:

Vc1=Vh+Vm but Vc2=k(Vh-Vm), the difference being the sign and the factor k.

A differential amplifier amplifies the difference between the two inputs, so (assuming a gain of one for now) we get

Vout= Vc1-Vc2= Vh+Vm-k(Vh-Vm)= Vh(1-k)+(1+k)Vm

If k=1, we get double the music voltage and complete cancellation of the hum voltage. But k is never exactly unity, so what is the effect of mismatch?

The cancellation ratio is (1-k)/(1+k). How large can k be to achieve 20 dB cancellation? For 20 dB, the cancellation ratio is one tenth, so 0.1=(1-k)/(1+k), and k= 0.8181, and 1-k=0.182. This means that if the coils are geometrically similar and differ in turns count by 18% or less, 20 dB or better cancellation will be achieved.

For 30 dB cancellation, 1-k= 6%.

Either way, take a look at the photo I posted of the circuit board inside the 81. That's where that schematic came from. The IC and one surface mount part is missing, but you could probably trace the circuit assuming they didn't use a double sided board. I've been meaning to do it but haven't had the time.The usual with surface mount cards is to use two-sided boards, perhaps with components on both sides, unless the circuit is so simple that it's cheaper to implement crossovers with wire bridges and drilled holes. So, I'd photograph both sides of the circuit board, and be sure to identify one corner with a magic marker such that it's visible in both photos.

Stan H

09-10-2008, 03:45 PM

If you want clean wind a low impedance coil and use a preamp to boost the level up. Just wind a regular humbucker with about 1000 turns on each coil. That will be as clean as an acoustic guitar.

Hi David, what size wire would you use for such a pickup, would 42 work or would you recommend something larger?

David Schwab

09-10-2008, 04:19 PM

In the circuit diagram, the coils are not in parallel. They are each connected to their own input of a differential amplifier, and so are electrically isolated from one another. Unlike a direct-wired electrical parallel connection, the coils do not load one another.

I knew that! That's what happens if you haven't thought through what you are going to type ... :o

The EMG-P is in parallel, but not the humbuckers. But I meant to say they aren't in series as you would expect.

The usual with surface mount cards is to use two-sided boards, perhaps with components on both sides, unless the circuit is so simple that it's cheaper to implement crossovers with wire bridges and drilled holes. So, I'd photograph both sides of the circuit board, and be sure to identify one corner with a magic marker such that it's visible in both photos.

Now that I think about it, the other side of the board is the back of the pickup, so there are no parts...

David Schwab

09-10-2008, 04:21 PM

Hi David, what size wire would you use for such a pickup, would 42 work or would you recommend something larger?

I did a bunch of bass pickups using 42 and 43. Generally you want heavier wire for a low Z pickup, but 42 worked fine.

I used a simple JFET preamp.

Stan H

09-10-2008, 09:44 PM

Thanks for the info, David!

Mike Sulzer

09-12-2008, 01:10 AM

Perfect matching is not required to obtain adequate hum cancellation.

Yes, I agree with your numbers. Another way of saying it is that you can approach 6 db better than implied by 1-k. That is, 1-k = .1 gives 25.58 db rather than 20 db, and 1-k = .01 gives 45.98 db rather than 40 db, while k-1=.31622 gives 14.53 db rather than 10 db, but only 4.53 db better than implied by 1-k.

But how much is good enough? Do you plan for the average environment, or the really bad one that might not be too common, but is still out there?

David Schwab

09-12-2008, 05:28 AM

But how much is good enough? Do you plan for the average environment, or the really bad one that might not be too common, but is still out there?

It's very common to mismatch PAF coils, and look at all the people who play Strats and Teles!

So how good is enough? Some people don't seem to mind the hum at all.

Mike Sulzer

09-12-2008, 01:43 PM

It's very common to mismatch PAF coils, and look at all the people who play Strats and Teles!

So how good is enough? Some people don't seem to mind the hum at all.

And look at how much effort there is to make strat pickups that sound like the original and have no hum.

David Schwab

09-12-2008, 01:57 PM

And look at how much effort there is to make strat pickups that sound like the original and have no hum.

Oh I agree. I don't use single coils. You can get away with it in a club, but I do a lot of recording, so I need quiet pickups.

Joe Gwinn

09-12-2008, 03:33 PM

Yes, I agree with your numbers. Another way of saying it is that you can approach 6 db better than implied by 1-k. That is, 1-k = 0.1 gives 25.58 db rather than 20 db, and 1-k = 0.01 gives 45.98 db rather than 40 db, while k-1=0.31622 gives 14.53 db rather than 10 db, but only 4.53 db better than implied by 1-k.Yes. The music voltage Vm is doubled when the coils are exactly matched, and doubling voltage causes a 20 Log10[2]= 6 dB increase. As the coils become increasingly mismatched, the 6 dB will decline, but the effect isn't that strong.

But how much is good enough? Do you plan for the average environment, or the really bad one that might not be too common, but is still out there?As a rule of thumb, 10 dB is quite noticable, 20 dB is pretty good (and would probably make the hum inaudible in a noisy venue), 30 dB is almost perfect, and 40 dB isn't any better than 30 dB in practice.

When people intentionally mismatch coils, the difference in turns count seems to be of order 10%, which would allow for very good cancellation: 20 Log10[(1-0.90)/(1+0.90)]= -25.6 dB.

This assumes that the electrostatic shielding is adequate. Perfectly matched coils are still susceptible to electrostatic pickup if not shielded.

Mike Sulzer

09-12-2008, 08:07 PM

As a rule of thumb,

I like your rules of thumb. Just like to point out that getting say 20db reliably time after time and under all condition requires aiming for somewhat better.

Perfectly matched coils are still susceptible to electrostatic pickup if not shielded.

Thank you for writing that: one of my pet peeves. In fact, writing that and arguing that it is correct contributed to me getting kicked off another forum. It is interesting that most humbucker users do not use a cover. But the base plate, even though it covers just the bottom, does have a significant shielding effect. So it could be worse.

David Schwab

09-12-2008, 11:56 PM

Thank you for writing that: one of my pet peeves. In fact, writing that and arguing that it is correct contributed to me getting kicked off another forum.

Yeah, but Mike, you would also argue about things, like when you said to me that stacking a bunch of magnets doesn't increase the strength, when clearly it does. (http://www.kjmagnetics.com/faq.asp#stack)

And Deb has a hair trigger for kicking people off lately...

It is interesting that most humbucker users do not use a cover. But the base plate, even though it covers just the bottom, does have a significant shielding effect. So it could be worse.

Because they don't sound the same with metal covers, which is why people started taking the covers off. You can get better noise reduction without changing the tone by using shielded plastic covers.

Traditional humbucker parts are really quite archaic. Covers are popular these days because of the way they look.

Joe Gwinn

09-13-2008, 04:16 AM

I like your rules of thumb. Just like to point out that getting say 20db reliably time after time and under all condition requires aiming for somewhat better.The rule of thumb was about the acoustic consquence of various levels of hum cancellation. This is inherently sloppy, as people are involved.

Achieving these levels of cancellation is another matter entirely. Although matching turns counts to within 10% doesn't seem that hard to me.

Thank you for writing that: one of my pet peeves. In fact, writing that and arguing that it is correct contributed to me getting kicked off another forum. Was it something you said?

What was their counterargument?

It is interesting that most humbucker users do not use a cover. But the base plate, even though it covers just the bottom, does have a significant shielding effect. So it could be worse.It's a tradeoff to be sure. Most covers do muffle the sound.

Mike Sulzer

09-13-2008, 09:31 PM

Yeah, but Mike, you would also argue about things, like when you said to me that stacking a bunch of magnets doesn't increase the strength, when clearly it does. (http://www.kjmagnetics.com/faq.asp#stack)

And Deb has a hair trigger for kicking people off lately...

David, I think we both know that stacking disc magnets, that is, flat things magnetized along the short dimension, increases the strength, and as your reference says, makes a magnet of the same strength as a single magnet of that geometry.

But making very long rod magnets out of shorter rod magnets has little effect. (magnetized along the long dimension) Do you remember what we were discussing?

It took Deb several years to kick me off, but yeah, the final event really was hair trigger, and kind of surprised me.

David Schwab

09-13-2008, 09:42 PM

Do you remember what we were discussing?

Yeah, I had about 10 neo bar magnets stuck together, and was able to pick up a chromed nickel silver Gibson EB-0 pickup cover. One or two of the same magnets wouldn't do it, and a big stack of ceramics wouldn't do it either.

I think the discussion was about the effect of chrome plating on the tone of a pickup.

This photo should refresh your memory.

Mike Sulzer

09-13-2008, 09:47 PM

Was it something you said?

What was their counterargument?

No counter argument necessary. On MIMF staff members are experts, and what they say is correct, period.

Charlie Falco claimed that:
1. The magnetic material in a pickup core does not affect the sensitivity to fields. Thus, a coil with with an air core can be used to cancel perfectly with one with a core of magnetic material.
2. Counter wound coils also cancel electric fields, not just magnetic fields.

He wrote that he learned all of this years ago by experimentation, and that any experiment that I did was simply wrong; he ignored any theoretical argument. The latter is understandable, of course. He knows nothing about the physics.

I suspect that there were some people reading this stuff who knew better, But I sure did not get much support.

David Schwab

09-14-2008, 12:16 AM

I suspect that there were some people reading this stuff who knew better, But I sure did not get much support.

I didn't agree with you about the air coil thing, but have since changed my stand on that. It does work though, since that's how Alembic does it. They have a plastic core in the hum canceling coil.

But having metal cores makes it more efficient. But if you look at a standard Gibson humbucker, the cores are hardly the same.

The DiMarzio stacked single coils have extra metal in the bottom coil (with no magnets), but also fewer windings than the top coil with the magnets. It works very well.

So they don't have to match, coil or core wise to cancel hum, and I think that was your argument.

Mike Sulzer

09-14-2008, 01:04 AM

I didn't agree with you about the air coil thing, but have since changed my stand on that. It does work though, since that's how Alembic does it. They have a plastic core in the hum canceling coil.

But having metal cores makes it more efficient. But if you look at a standard Gibson humbucker, the cores are hardly the same.

The DiMarzio stacked single coils have extra metal in the bottom coil (with no magnets), but also fewer windings than the top coil with the magnets. It works very well.

So they don't have to match, coil or core wise to cancel hum, and I think that was your argument.

When the two coils are the same, as they were in Charlie's measurement you do need the magnetic core to get the same sensitivity to magnetic fields. The measurement I made at the time gave a 14 db increase in hum when the screws in a PAF type were removed. Proof enough I would have thought, especially since someone had earlier described a similar measurement. Didn't I write recently that the longer length of the screws (and I should mention the large head as well) counteracts the smaller diameter compared to the slugs? I think the sensitivity of the two coils is thus about the same.

Of course you can use an air core for a dummy if it is some combination of larger/greater number of turns.

By the way, in that other discussion you mentioned, were you not concerned with why the ceramics would not do it no matter how many you used in the stack? That would be for the reason I mentioned above.

David Schwab

09-14-2008, 11:14 PM

When the two coils are the same, as they were in Charlie's measurement you do need the magnetic core to get the same sensitivity to magnetic fields. The measurement I made at the time gave a 14 db increase in hum when the screws in a PAF type were removed. Proof enough I would have thought, especially since someone had earlier described a similar measurement. Didn't I write recently that the longer length of the screws (and I should mention the large head as well) counteracts the smaller diameter compared to the slugs? I think the sensitivity of the two coils is thus about the same.

Of course you can use an air core for a dummy if it is some combination of larger/greater number of turns.

Right, but as I have said in the past, in the real world it's not always that way. Alembic wind both coils exactly the same, and they are wired in series, so they aren't mixing the two to get them to cancel. The top coil has a magnet, and the dummy has nothing except a plastic spacer the same size as the magnet of the top coils.

And you talked about removing the screws from a humbucker coils and it changing the rejection of noise, but the two cores were never equal to start with!

Then there's the Suhr Guitars system that uses a low resistance larger area coil. Dummy coils seem to be going in that direction as to not effect the string sensing coil's tone. They don't get 100% rejection, but they don't really need to.

By the way, in that other discussion you mentioned, were you not concerned with why the ceramics would not do it no matter how many you used in the stack? That would be for the reason I mentioned above.

The ceramics also get stronger stacked up, it's real obvious when you start stacking them and try to lift objects. But my point was that the neos are so strong that they were able to lift the cover. One of those neos is as strong as that whole stack of ceramics. I've recharged ceramics with two of the neos.

I can pull the ceramic apart, but it's hard to pull the neos off the stack. I just got a stack of 30 neos, and it was a real chore to get one off!

Joe Gwinn

09-15-2008, 02:10 AM

No counter argument necessary. On MIMF staff members are experts, and what they say is correct, period.

Charlie Falco claimed that:
1. The magnetic material in a pickup core does not affect the sensitivity to fields. Nonsense.

Thus, a coil with with an air core can be used to cancel perfectly with one with a core of magnetic material.This can work, if the area-turns-permeability products of the two coils match reasonably well.

Counter wound coils also cancel electric fields, not just magnetic fields.Nonsense.

He wrote that he learned all of this years ago by experimentation, and that any experiment that I did was simply wrong; he ignored any theoretical argument. The latter is understandable, of course. He knows nothing about the physics.Nor were his experiments well enough designed.

I suspect that there were some people reading this stuff who knew better, But I sure did not get much support.Given that it got you bounced, one can understand their reluctance.

salvarsan

09-15-2008, 02:41 AM

... one can understand their reluctance.(Aaaaaargh.)

Must ... not ... make ... vile ... pun.

-drh

Mike Sulzer

09-15-2008, 06:23 AM

Right, but as I have said in the past, in the real world it's not always that way. Alembic wind both coils exactly the same, and they are wired in series, so they aren't mixing the two to get them to cancel. The top coil has a magnet, and the dummy has nothing except a plastic spacer the same size as the magnet of the top coils.

I do not know what kind of magnet they use, but if a magnet alone is used as the core and it has low permeability, such as neo, then an air core dummy would be the proper thing to use. Using a neo magnet alone is like using an aircore.

And you talked about removing the screws from a humbucker coils and it changing the rejection of noise, but the two cores were never equal to start with!

And your evidence for that is???? Of course two cores that are physically different can have the same sensitivity if they are designed to. Give the engineer who designed the Gibson humbucker some credit. Some people actually do understand what they are doing.

Then there's the Suhr Guitars system that uses a low resistance larger area coil. Dummy coils seem to be going in that direction as to not effect the string sensing coil's tone. They don't get 100% rejection, but they don't really need to.

No reason why they cannot get good rejection with that system, at least over a fairly wide range of harmonics.

The ceramics also get stronger stacked up, it's real obvious when you start stacking them and try to lift objects. But my point was that the neos are so strong that they were able to lift the cover. One of those neos is as strong as that whole stack of ceramics. I've recharged ceramics with two of the neos.

Of course the stack gets stronger, up to a point.

David Schwab

09-15-2008, 05:20 PM

I do not know what kind of magnet they use, but if a magnet alone is used as the core and it has low permeability, such as neo, then an air core dummy would be the proper thing to use. Using a neo magnet alone is like using an aircore.

Ceramic. They have no metal parts in the pickup.

And your evidence for that is???? Of course two cores that are physically different can have the same sensitivity if they are designed to. Give the engineer who designed the Gibson humbucker some credit. Some people actually do understand what they are doing.

Seth Lover didn't want the adjustable screws, and he didn't design the pickup that way. The prototype used for the patent had two sets of non adjustable slugs. He said Gibson wanted adjustable poles to make the pickup more marketable, since the P-90 had them, and Fender didn't.

The screw coil is weak, you can hear it for yourself.

No reason why they cannot get good rejection with that system, at least over a fairly wide range of harmonics.

The samples I have heard sound very good. If you've ever worked with dummy coils you find out they can ruin the tone of the string sensing coil. The Kinman/DiMarzio method works really well too.

Of course the stack gets stronger, up to a point.

Of course... it couldn't be stronger than a single magnet of the same size and type, but it is as strong.

Mike Sulzer

09-15-2008, 05:59 PM

Ceramic. They have no metal parts in the pickup.

What is the permeability of the ceramic that they use?

The screw coil is weak, you can hear it for yourself.

If the screw coil sounds weak, then it must be at least several db down. If this is a reflection of how well the pickup cancels hum, then it cannot do it very well. Actually, it is more complicated than that. Changing the height of the screws changes the signal strength (from the string) a lot because the string is close. But it does not change the sensitivity to hum as much if you do not move too far because the hum source is far away and the screws are longer than the height of the coil.

So what does your observation that the screw coil is weak mean? It certainly does not demonstrate that the screw coil has a weaker sensitivity to hum.

The samples I have heard sound very good. If you've ever worked with dummy coils you find out they can ruin the tone of the string sensing coil. The Kinman/DiMarzio method works really well too.

Of course. The idea is to make a low inductance coil with the same sensitivity to hum and put it in series rather than double the inductance and kill the highs with a coil like the pickup coil. Am I missing your point?

Of course... it couldn't be stronger than a single magnet of the same size and type, but it is as strong.

That is not the issue. What happens as you make the stack deeper? Does each additional magnet added to the back of the stack increase the strength at the other end as much as the previous magnet did. If there is a decrease, what factors affect it?

David Schwab

09-16-2008, 05:59 PM

What is the permeability of the ceramic that they use?

I have no idea. But, yes a ceramic magnet is closer to an air core than an alnico.

So what does your observation that the screw coil is weak mean?

That maybe there is less metal in the screw coil? It might also be less efficient because the screws extend out the back.

It certainly does not demonstrate that the screw coil has a weaker sensitivity to hum.

If the coils are the same, but the inductance is different, they should throw that off, no? That's what you were pointing out about removing the screw poles.

I agree that everything should be matched ideally. And that's what I would want to do with a new pickup design, but my point has always been that it hasn't been done that way so far, and still works well enough. But there's always room for improvement.

Of course. The idea is to make a low inductance coil with the same sensitivity to hum and put it in series rather than double the inductance and kill the highs with a coil like the pickup coil. Am I missing your point?

My point was that the dummy coil in these systems has an air core, while the pickup does not. This is similar to the situation described by you when you removed the screws from the coil. Obviously with the Suhr system, the larger area of the coil makes up for the lack of a core.