"Neutral" or "DNE" - Darn Near Eddyless - Humbucker?

[Charlie Honkmeister]

So here's the quest(ion) -  if we had a Gibson humbucker size pickup with as close to zero eddy losses as possible,  then wouldn't we have more design freedom to engineer the response electrically to be closer to anything we wanted,  including getting pretty close to emulating a slew of other humbuckers?  

Some of this thread was sparked long ago with a set of Joe Barden Two/Tone HB's that I purchased back in 1998 or so.   I was trying to figure out just how the Two/Tone could get so close to the single coil type tonality, without dropping volume like a conventional coil tapped approach.  

Fortunately or unfortunately,  I blew up the neck pickup beyond repair,  trying to get a new longer cable soldered to it  (what kind of decision was it to use flea clips instead of grommets to terminate the coil wires !?!) ,   and stripped it to see what was going on.   I still have the bridge Two/Tone and the skeleton of the neck PU  available for pics if anyone is interested .

So,  it looks like several things were done,  and it looks like I can get close with off the shelf Mojotone parts.  

Here's some of the "features"  of the Two/Tone.   Of course,  it's a double rail pickup.

1.  No metal parts in the whole darned thing except for thin steel rails inside the coils.  Unless you want to count the two thin strips of  copper tape which  ground the rails and the two ceramic magnets.    The baseplate and bobbin tops are plastic/phenolic.

2. Rather conventional rail bobbins.  One small ceramic magnet per rail, positioned outboard of the rail relative to the center of the pickup.  

3. The "two/tone" feature is done by tapping both coils at about the 60% point and bringing out two wires for the taps along with the normal two wires per coil for coil start and coil end.  

Just as a FYI,  with the Mojotone 53 mm fiber baseplate,  and their rails, magnets and rail bobbins,  it might be possible to make a "faux Barden" ,  albeit the Mojotone rails are somewhat thicker than the JB rails.   So...  maybe laminated rails?  How far do we want to pursue reducing eddies? 

I could care less about the two/tone feature because of my variable resonant frequency / variable cap control buffer.    If I can get the inductance in the 1 Henry range and the self-resonance about 10K,   we should be able to get just about any combination of resonant frequency and Q we want within reason. 

Comments?   Looking for some encouragement to actually pursue doing this.  I have the Mojotone parts in hand already and wouldn't take much to take these to Sonny Walton (who has a much better winder than I do)  and wind some up.   

Thanks,

Charlie 

[stratotarts]

Not to say that it wouldn't be an acceptable design, but using steel pole pieces goes against your design goal. The parts that are closest to the string make the biggest difference when it comes to eddy currents. For what you're talking about, magnetic pole pieces are "de rigeur" - have a look at the Gibson Firebird: link

[Charlie Honkmeister]

Ken,

Thanks - what I was getting at was "minimal" eddy losses.  We have to have some ferromagnetic material in play to guide the field and increase the inductance since an air coil pickup would be too large to fit any of the standard packages and it would be a bear to get the magnetic field guided to the strings.  Halbach arrays, anyone?     So,  steel rails but not too large,  like a Joe Barden HB or a Bill Lawrence L-500 or L-90.   

The only other design I have seen which might work fine would be a humbucker with 12 individual magnets in the pole piece positions, like two traditional Strat pickups next to each other,  and a non-metallic base. 

A slightly underwound Firebird design is tempting.  The mini-humbucker size (aperture width)  is really underrated IMHO.  Paul Reed Smith is doing some PU's in that approximate size for some of their models.  

[ms]

Jan 4, 2017 10:22:45 GMT -5 Charlie Honkmeister said:

Ken,

We have to have some ferromagnetic material in play to guide the field and increase the inductance since an air coil pickup would be too large to fit any of the standard packages and it would be a bear to get the magnetic field guided to the strings.   

Ferromagnetic material does not have to be conductive.  There are ferrites that can do the job with any permeability that you  want.

If you want to get permanent field to the strings in an air core pickup, just use Neo magnets inside the coil under the strings. Neo's permeability is about 2% higher; so it is effectively the same.  If you want such an air core pickup for some reason, use very fine wire.

[antigua]

Jan 3, 2017 23:59:11 GMT -5 Charlie Honkmeister said:

So here's the quest(ion) -  if we had a Gibson humbucker size pickup with as close to zero eddy losses as possible,  then wouldn't we have more design freedom to engineer the response electrically to be closer to anything we wanted,  including getting pretty close to emulating a slew of other humbuckers?  

Some of this thread was sparked long ago with a set of Joe Barden Two/Tone HB's that I purchased back in 1998 or so.   I was trying to figure out just how the Two/Tone could get so close to the single coil type tonality, without dropping volume like a conventional coil tapped approach.  

Fortunately or unfortunately,  I blew up the neck pickup beyond repair,  trying to get a new longer cable soldered to it  (what kind of decision was it to use flea clips instead of grommets to terminate the coil wires !?!) ,   and stripped it to see what was going on.   I still have the bridge Two/Tone and the skeleton of the neck PU  available for pics if anyone is interested .

So,  it looks like several things were done,  and it looks like I can get close with off the shelf Mojotone parts.  

Here's some of the "features"  of the Two/Tone.   Of course,  it's a double rail pickup.

1.  No metal parts in the whole darned thing except for thin steel rails inside the coils.  Unless you want to count the two thin strips of  copper tape which  ground the rails and the two ceramic magnets.    The baseplate and bobbin tops are plastic/phenolic.

2. Rather conventional rail bobbins.  One small ceramic magnet per rail, positioned outboard of the rail relative to the center of the pickup.  

3. The "two/tone" feature is done by tapping both coils at about the 60% point and bringing out two wires for the taps along with the normal two wires per coil for coil start and coil end.  

Just as a FYI,  with the Mojotone 53 mm fiber baseplate,  and their rails, magnets and rail bobbins,  it might be possible to make a "faux Barden" ,  albeit the Mojotone rails are somewhat thicker than the JB rails.   So...  maybe laminated rails?  How far do we want to pursue reducing eddies? 

I could care less about the two/tone feature because of my variable resonant frequency / variable cap control buffer.    If I can get the inductance in the 1 Henry range and the self-resonance about 10K,   we should be able to get just about any combination of resonant frequency and Q we want within reason. 

Comments?   Looking for some encouragement to actually pursue doing this.  I have the Mojotone parts in hand already and wouldn't take much to take these to Sonny Walton (who has a much better winder than I do)  and wind some up.   

Thanks,

Charlie 

I'm not sure what the necessity is behind the double rail design, but if you absolutely needed rails, laminations would take care of the eddy currents. 

As far as a coil tapped humbucker retaining the same output, improving upon series/parallel; I bet that's not strictly true, as it's lowering the inductance in "tapped mode", but it's probably not nearly as low of an inductance as parallel mode. If the capacitance is somehow kept lower through the tapping, it will also yield a higher resonant peak for a higher inductance, or overall voltage output. The real evil of parallel mode is that you have a low inductance, but still a very high capacitance. Normally, low peak means high voltage, but a parallel humbucker essentially robs you of both. 

If you want a high Q factor, that's not hard to do, you just have to do as Fender does and stick to plastic, fiber and magnet in the construction. If you use ceramic or neodymium, the only damping losses that will exists are those that owe to the wire resistance. In general, such a high Q factor is unusable, Fender uses 250k pots just to further dampen the Q factor of their single coils. A pickup with a very high resonant peak is essentially flat, so it would be a good platform for tone shaping, which they claim is the basis of the Fishman Fluence's tone shaping, again prompting the question, why only two voicings? I was never clear on what technical benefits the Fluence enjoyed due to the PCB layered coil design.

Since we're on the subject, I discovered something I believe is not common knowledge, when you tap a coil and the other side of the coil is still connected at one end, it does not conduct current, but it does still cause a very high capacitance to occur. On the Seymour Duncan SSL-4, the tapped resonant peak suggests that the unused portion of coil added about 450pF of capacitance, which is equivalent to an other 12ft or so of guitar cable. Yes, it's that bad. I always wondered by Seymour Duncan's tap point would cut the coil in half, rather than say, cut it down by 3/4, and that's the reason. You have to cut the inductance down that far in order to offset the very high capacitance, and output voltage suffers greatly as a result. It's a design flaw, IMO. If you do a coil tap, and you want to retain high output, you should use a four conductor cable so that the outer portion of coil can be disconnected at both ends. You can then set the tap point later in the wind, say the 3/4 or 4/5ths mark, knowing that the extra guitar cable's worth of capacitance won't be raining on your inductance. 

[Charlie Honkmeister]

Jan 4, 2017 12:25:52 GMT -5 antigua said:

Jan 3, 2017 23:59:11 GMT -5 Charlie Honkmeister said:

I'm not sure what the necessity is behind the double rail design, but if you absolutely needed rails, laminations would take care of the eddy currents. 

As far as a coil tapped humbucker retaining the same output, improving upon series/parallel; I bet that's not strictly true, as it's lowering the inductance in "tapped mode", but it's probably not nearly as low of an inductance as parallel mode. If the capacitance is somehow kept lower through the tapping, it will also yield a higher resonant peak for a higher inductance, or overall voltage output. The real evil of parallel mode is that you have a low inductance, but still a very high capacitance. Normally, low peak means high voltage, but a parallel humbucker essentially robs you of both. 

If you want a high Q factor, that's not hard to do, you just have to do as Fender does and stick to plastic, fiber and magnet in the construction. If you use ceramic or neodymium, the only damping losses that will exists are those that owe to the wire resistance. In general, such a high Q factor is unusable, Fender uses 250k pots just to further dampen the Q factor of their single coils. A pickup with a very high resonant peak is essentially flat, so it would be a good platform for tone shaping, which they claim is the basis of the Fishman Fluence's tone shaping, again prompting the question, why only two voicings? I was never clear on what technical benefits the Fluence enjoyed due to the PCB layered coil design.

Since we're on the subject, I discovered something I believe is not common knowledge, when you tap a coil and the other side of the coil is still connected at one end, it does not conduct current, but it does still cause a very high capacitance to occur. On the Seymour Duncan SSL-4, the tapped resonant peak suggests that the unused portion of coil added about 450pF of capacitance, which is equivalent to an other 12ft or so of guitar cable. Yes, it's that bad. I always wondered by Seymour Duncan's tap point would cut the coil in half, rather than say, cut it down by 3/4, and that's the reason. You have to cut the inductance down that far in order to offset the very high capacitance, and output voltage suffers greatly as a result. It's a design flaw, IMO. If you do a coil tap, and you want to retain high output, you should use a four conductor cable so that the outer portion of coil can be disconnected at both ends. You can then set the tap point later in the wind, say the 3/4 or 4/5ths mark, knowing that the extra guitar cable's worth of capacitance won't be raining on your inductance. 

Antigua,

Thanks for your comments!

I don't necessarily have to have a rail design,  just used the Barden Two/Tone as an example, and also it's easier to play with laminations or thinner material with a filler on a rail design,  than it would be to do the same thing with a polepiece design. 

Also,  with a rail design,  there's no worry about polepiece spacing and having the polepieces line up for different string spreads, or dropout on big string bends.  

Really,  reducing eddies and inductance would be a way to get a high self-resonant frequency with high Q as you said,  which could be damped down with loading and capacitance to whatever was desired.   Reducing the iron content of the cores/rails would probably allow more turns for greater output for the same inductance.

The main idea of reducing eddies is probably secondary to reducing inductance,  but the idea is to have the most output and clarity possible, and do all voicing external to the pickup.

That's interesting about what you discovered with a connected section of the coil on a coil tap.  

-Charlie

[Charlie Honkmeister]

Jan 4, 2017 11:41:48 GMT -5 ms said:

Jan 4, 2017 10:22:45 GMT -5 Charlie Honkmeister said:

Ken,

We have to have some ferromagnetic material in play to guide the field and increase the inductance since an air coil pickup would be too large to fit any of the standard packages and it would be a bear to get the magnetic field guided to the strings.   

Ferromagnetic material does not have to be conductive.  There are ferrites that can do the job with any permeability that you  want.

If you want to get permanent field to the strings in an air core pickup, just use Neo magnets inside the coil under the strings. Neo's permeability is about 2% higher; so it is effectively the same.  If you want such an air core pickup for some reason, use very fine wire.

That's true.  Ceramic magnets aren't conductive AFAIK.  I didn't remember that about Neo magnets as well.   The basic idea is to reduce inductance increase caused by the magnet and magnetic structure,  so we can get more turns on the coil and get more output.  But like anything else, there's a tradeoff with winding capacitance of course.

In parallel coil mode,  several "vintage neck"  pickups are self-resonant at about 10 Khz with fairly decent Q -  12+ dB peaks.  The tradeoff is 6 dB less output than series coil mode, which I don't think is a big deal at all.   I'm still testing a couple,  but I may not need to go very far to get close to the goal.    

[antigua]

Rather than a rail, you could just use a bar magnet as the rail. Seymour Duncan does this with some of their humbuckers:




You might have to grind it down to size, though. You have to make sure the poles of the magnets exit along the sides, and not out of the faces.

[Charlie Honkmeister]

Jan 4, 2017 16:38:00 GMT -5 antigua said:

Rather than a rail, you could just use a bar magnet as the rail. Seymour Duncan does this with some of their humbuckers:




You might have to grind it down to size, though. You have to make sure the poles of the magnets exit along the sides, and not out of the faces.

 Yes,  that's a valid approach and I think the Firebird PU is made this way.

Here's the Mojotone parts for the rail PU I was mentioning.  This one can use either two or four ceramic magnets which are next to the rails.  In the Barden,  the 2 ceramic magnets are on the outside as shown here, and there is a plastic spacer that fills the middle of the PU under the bobbins.
  






Please excuse the extra dirt;  I had to dig these out of a supposedly sealed box on the garage workbench.   

[ms]

Jan 4, 2017 16:33:57 GMT -5 Charlie Honkmeister said:

Jan 4, 2017 11:41:48 GMT -5 ms said:

Ferromagnetic material does not have to be conductive.  There are ferrites that can do the job with any permeability that you  want.

If you want to get permanent field to the strings in an air core pickup, just use Neo magnets inside the coil under the strings. Neo's permeability is about 2% higher; so it is effectively the same.  If you want such an air core pickup for some reason, use very fine wire.

  The basic idea is to reduce inductance increase caused by the magnet and magnetic structure,  so we can get more turns on the coil and get more output. 

I think you are seriously confused.  Permeability that increases the inductance also increases the output.

[antigua]

In fact, inductance via permeable core is superior to inductance via wind count, because you don't suffer the capacitance increase with a permeable core. DiMarzio patented the idea of putting permeable material in the "dead space" between the slugs and screws to get a higher inductance for fewer winds, which is a shame, because it's pretty much an all around good idea. One way to go, if you have the means, is the have the entire bobbin be a permeable body, like a pot core inductor. You can get the same inductance, probably with a shockingly low number of turns of wire. 

One reason I'm not thrilled about the idea of inventing a space aged pickup is that with all the patents accumulated over the past 70 years, chances are the idea was patented in the 70's or 80's and then I'd have to pay some amount of money to a dead beat, who's probably on oxygen, who never went anywhere with the long forgotten idea he'd patented. Besides, and this is something else to take note of, guitarists have by and large rejected new concepts. DiMarzio employs some of their patented methods in their more recent pickups, but doesn't mention the fact at all in the product copy, likely out of fear that they would scare away guitarists. For example, the "PAF Master" is supposed to invoke a mental picture of vintage authenticity, and yet its an "airbucker" with enhanced ferrous cores. Companies like Lace seem to flail with their highly visual futuristic ideas.


I gotta be honest, Strats, Tele and LP's look very 50's. Futuristic (80's-present) looking pickups clash with them. I've begged, as a consumer, for Lace and Zexcoil to give their new pickup designs a more vintage look, as I'm on the fence about them otherwise. 

[Charlie Honkmeister]

For a target inductance,  you can have more winds and less metal core,  or less winds and more metal core.  That's what I was trying to get across,  sorry if that wasn't phrased in a good way.  

[stratotarts]

Jan 4, 2017 17:50:38 GMT -5 antigua said:

In fact, inductance via permeable core is superior to inductance via wind count, because you don't suffer the capacitance increase with a permeable core. DiMarzio patented the idea of putting permeable material in the "dead space" between the slugs and screws to get a higher inductance for fewer winds, which is a shame, because it's pretty much an all around good idea. One way to go, if you have the means, is the have the entire bobbin be a permeable body, like a pot core inductor. You can get the same inductance, probably with a shockingly low number of turns of wire. 

One reason I'm not thrilled about the idea of inventing a space aged pickup is that with all the patents accumulated over the past 70 years, chances are the idea was patented in the 70's or 80's and then I'd have to pay some amount of money to a dead beat, who's probably on oxygen, who never went anywhere with the long forgotten idea he'd patented. Besides, and this is something else to take note of, guitarists have by and large rejected new concepts. DiMarzio employs some of their patented methods in their more recent pickups, but doesn't mention the fact at all in the product copy, likely out of fear that they would scare away guitarists. For example, the "PAF Master" is supposed to invoke a mental picture of vintage authenticity, and yet its an "airbucker" with enhanced ferrous cores. Companies like Lace seem to flail with their highly visual futuristic ideas.


I gotta be honest, Strats, Tele and LP's look very 50's. Futuristic (80's-present) looking pickups clash with them. I've begged, as a consumer, for Lace and Zexcoil to give their new pickup designs a more vintage look, as I'm on the fence about them otherwise. 

Sure. Look what happened to Dialtone Pickups:
before and after

[Charlie Honkmeister]

The rule of thumb target inductance for doing the whiz-bang variable resonant frequency things,  is about 1 Henry give or take about .2 H.   The idea on using less metal is to reduce eddy current loss to a minimum, so the pickup by itself is more "neutral". 

Output isn't necessarily the biggest thing to optimize.  What we're trying to go for is a "baseline"  good large humbucker design with decent output which we can voice any way we want to.     

What I have so far which is working well with the buffer design is approximately:

1 to 1.2 Henry  inductance
1.9  to 2.2 K DCR
110-220 pF capacitance (measured with LCR meter, end of the cable, windings to ground.  Not calculated from resonance so is probably off)

In parallel coil mode,  these inexpensive ($8.50 or so) Strat-sized humbucker pickups hit these numbers and are self-resonant at about 10 KHz :


 
Just trying to get a full-sized humbucker solution in the same range.   

Antigua,  I am not completely sold on rails, but since without doing a lot of rwinding,  I have to use neck humbuckers with 50 mm pole spacing.  I will try to get some of the bridge PU's I have rewound for lower inductance,  and will absolutely have a low-wind conventional looking set which I can point to and say that it works with the variable voicing.   Very good point about conventional looks.  But rail PU's  do look great IMHO on a Strat or Tele. 

 

[antigua]

One thing to keep in mind about pickup response modelling, too, is that eddy currents aren't strictly the same as resonant damping. Eddy currents present a more dynamic load, and they impose an additional -6dB/octave low pass. For example, check out the Gretsch Filter'tron plot:




The scale is 1dB per vertical division, so in the "loaded" plots there is only a 2dB drop between 300Hz and 4kHz, so it's rather flat, but it has a "hard knee", there's a sharp -18dB/oct drop off, where as if you just add parallel resistance load, the drop off is only -12dB/oct, so it's a softer knee, and that might sound a little different, I don't know how different.

[Charlie Honkmeister]

It's such a pleasure to have detailed data to compare, to see a point somebody's making.  

Yes,  your plots absolutely confirm the effects of eddies that I first read about in Lemme's article.   Also hats off to Ken (stratotarts) for his very interesting and well-researched data and experiments on eddies in pickup covers.

About all I can say at this point is that I'm going to go forward with the Mojotone rails build and given that it doesn't have a metal baseplate or a cover, it should be at least "pretty good"  on eddy effects.    I'm going to shoot for hi-fi clarity to start with,  and see where that goes sound-wise.

I have a Syscomp CGM-101, driver coil,  DE-5000 LCR meter, etc.  so at least in theory I can do the same sorts of measurements if need be.  I will ask stratotarts about an integrator; was thinking about doing it in software but the integrator will allow better dynamic range methinks.  

Thanks so much for your responses, guys.  Will update this thread as things progress.  

-Charlie