Fully differential guitar setup?

[Matador]

I've been thinking, after helping someone battle noise in his Fender Strat single-coil setup.  It was humming like mad, and after the traditional shielding job it improved - probably about as good as can be had from such a setup.

It seems to me that the inherent flaw in the setup is that essentially the pickup is converted to an unbalanced source as it enters the body of the guitar since we're referencing all internal voltages to one side of the coil (aka. 'grounding' one side of the coil).  Hence any pickup of electrical noise will always be at full reference to this internal node, and there's no way to cancel it, only reduce it in magnitude.  No amount of clever shielding will work, since the pickup coil will essentially always be exposed to the outside world.

So here enters the humbucking pickup, with its two opposite magnet orientations, and two coils that have opposite current flow, hence any common mode AC signal placed across both windings will cancel out, however the magnetic induction (via the vibrating guitar strings) will add together (assuming series wiring).  However these don't sound the same.

Is there any way to get a regular single coil pickup to be hum free without resorting to splitting the coils and converting them to some form of humbucking configuration that changes the sound?

It seems to me we could center-tap a regular single coil pickup, without changing the winding orientation of the coil (which is how almost all 'single coil but noiseless' pickup designs work).  Hence we would wind our single coil pickup no differently than before,  with the exception that halfway through we would place a center-tap, then complete the wind.  The center tap would become the new reference point, just like would be done in a full-wave rectification setup, so the coil would spit out a differential AC signal, with each end of the coil 180 degrees opposite in phase to the center point, just like in a full wave rectified power transformer.

The tone / volume controls would be placed just like before, across the coil(s), however exiting the guitar would be essentially a differential signal, plus a ground, just like the coil of a dynamic microphone, although of much higher output impedance.  This could be wired into a a regular stereo jack and all that would be needed is a pedal that converts the differential input into a single-ended low impedance output.  Or, the input to the amp could be designed to do this natively.  In order to keep the common mode input range of the pickup tracking with the receiver, the shield of the cable can be tied to the pickups common mode center tap point.

By my reasoning, this setup should be common mode noise cancelling, like a humbucker, however the tone of the pickup shouldn't be impacted like it is with all of the other humbucking configurations.  And no other internal shielding of the guitar or the wiring should be needed either.

Thoughts?  I'm certainly not the first person who has thought about this, but I haven't seen this discussed previously on GroupDIY.

 

[Martin Griffith]

I did this (quite badly) many decades ago.Pre surface mount days. These days I would might try doing it with P48/phantom powering. Just buffering with a TL072, would get rid of a lot of hum problems and sending balanced, but with only one line driven would keep most of the CMRR advantages. A hum bucker wasn't needed in my case, but was added for fun, with  a pot to trim for minimum smoke.

M

 

[JohnRoberts]

I'm not sure how much it would help. The hum is being converted to voltage by the coil and not really a common mode noise that could be cancelled out.

humbucking pickup coils use two pickups wired in series such that the guitar sound adds and hum cancels but these sound different than single coil pickups.

JR

 

[gyraf]

Izotope rx is a useable solution. . .

Jakob E.

 

[benb]

There are two possible sources of hum - magnetic (which pickups are quite sensitive to), which the humbuckers (pretty much) cancel out. You can tell magnetic hum because it varies with how close the pickup is to the source (almost always a power transformer, as in an amplifier, organ, synthesizer, mixing board, whatever), AND the angle of the pickup to the transformer. Without going to humbuckers, the solution is to keep the guitar as far as possible away from every electronic device that's plugged in.

There's also electrostatic. If you get hum with the guitar by itself and the hum goes away if you touch the strings or the ground of the output jack, that's electrostatic. Using foil to shield the cavity and pickguard (connecting all conducting shield parts to a ground connection in the guitar) is what helps this.  This still may not fully eliminate it unless the pickup also has a conductive shield around it connected to ground, as do many humbuckers. The "hot" side of the coil is still exposed.

That may be a problem with wiring a pickup as "balanced" (such as using an instrumentation to keep the load on the pickup high impedance), in that there's still likely one "side" of the pickup that's more susceptible to electrostatic pickup than the other. I found this out by adding a phase switch for each pickup on a Stratocaster. Touching a pole piece gave more hum with the switch in one position than in the other. Apparently the inner part of the winding got capacitively coupled to the pole piece, and the inner part was intended as the "ground" side.  So single-coil pickups are inherently unbalanced from an electrostatic position as well.

There was a Les Paul "Recording" guitar made decades ago, it was made with low-impedance pickups and a XLR connector to go directly into a balanced mic input. The frequency response was flat, and apparently no one liked it. That's also one possible "problem" with going active with traditional pickups - the high-impedance coil resonates with itself and/or the guitar cables capacitance to give a frequency boost in the 5k to 8k range, and to a lot of people that's "the sound of a guitar."

 

[Newmarket]

It seems to me we could center-tap a regular single coil pickup, without changing the winding orientation of the coil (which is how almost all 'single coil but noiseless' pickup designs work).  Hence we would wind our single coil pickup no differently than before,  with the exception that halfway through we would place a center-tap, then complete the wind.  The center tap would become the new reference point, just like would be done in a full-wave rectification setup, so the coil would spit out a differential AC signal, with each end of the coil 180 degrees opposite in phase to the center point, just like in a full wave rectified power transformer.

I don't see the need for the centre tap. Just take the signals from the ends of the  (ungrounded) coil and treat it like mic output (albeit Hi-Z) ? But you'd need a suitable differential input in or near the amp.
Of course - single coil guitars usually have more than one pickup (obvs three on a standard Srat') and these can be switched to be joined in various permutations which would add to the 'fun'...

 

[JohnRoberts]

Balanced differential signal interface will help maintain the integrity of the signal going somewhere else, but if the hum is being decoded by the pickup internally, the perfect interface will just deliver the hum perfectly too.

This is a pretty old and well inspected problem.

JR

 

[Newmarket]

Balanced differential signal interface will help maintain the integrity of the signal going somewhere else, but if the hum is being decoded by the pickup internally, the perfect interface will just deliver the hum perfectly too.

This is a pretty old and well inspected problem.

JR

Yeah - when it comes down to it magnetic pickups will err..pick up err...magnetic fields Lower inductance windings are a possible alternative route to the Humbucking configuration (which gives rise to frequency cancellation issues - fine if that's what you want - PAF / P90 et al but not so good for the classic Strat' tones).
But , as written about in the thread, the sound of those on electric guitar has not generally been well received. Maybe someone will try again ?
On bass guitar low impedance pickups have had better luck.

 

[abbey road d enfer]

There's a big misunderstanding here. Magnetic p/u's are sensitive to magnetic field. As a result the sensitivity to external fields of single-coil (non-humbucking) p/u's is proportional to their response to string movement, so whatever the impedance and balance choices, the ratio between wanted signal and hum is the same, as long as the effects of electrostatic interference are kept under control, which means proper shielding and use of quality cables.
There is an excellent answer to single-coil noise, which is used by MusicMan and a few others; a low-impedance humbucking coil. Being low-Z it does not impair the desired single-coil sound (in fact there's a bit of 9V-powered electronics to make it work).

 

[CJ]

single coil noise? no free lunch, otherwise Fender would have fixed the problem 70 years ago.

even humbuckers can get noisy at some clubs where they have hideous power quality and dimmers everywhere,

how many ohms are the pickups? a lot of guitar companies are winding hot pickups with mega turns in order to get you to buy them,

shielding helps , and making sure the bridge is grounded well also helps, maybe a little coax helps,

5 position strats will have  have canceling in two positions if you have bad EMI problems,

but then you are stuck with that country nasal sound, not gonna work on Voodoo Child, 

single coil humbuckers are getting better now so maybe shop around to see the latest stuff, close to LA?

Namm is coming up, 

engineers will tell you to kill the hum at the source,  but since that is out of our hands, then check this out>

http://www.ilitchelectronics.com/

 

[Chris_V]

As said before this will not help since main source of hum is the pickup itself, balanced or not.
Shielding of the pickup cavity and pickguard (if there is one) can help a lot even if it can have some influence on the high end response of the pickup. No real proof on that, and since I play bass I don't care  ;D
I have a modified shoeps circuit (low impedance, balanced output, phantom powered) in my bass for more than ten years. I even designed a specific bass preamp to work with, with an effect loop in order to be able to use pedals. It works fine, but the gain is not that important with regard to a more traditional setup !

 

[abbey road d enfer]

then check this out>

http://www.ilitchelectronics.com/

This is clearly a system with a separate humbucking coil, not too dissimilar to the MusicMan system. The electronics are necessary for adjusting optimum hum rejection.

 

[clintrubber]

single coil noise? no free lunch, otherwise Fender would have fixed the problem 70 years ago.

The weird thing is that some of their instruments have a/the solution: split PU's (like P-bass, Electric XII)

I might be overlooking something here, but it seems the way to go (be it at additional cost vs a single PU).

BTW, Fender at least provides that with the PU-switch in middle position (on a 2 PU instrument) there's  (an usable amount of) hum cancelling because of RWRP.

Other brands, like Rickenbacker for instance, don't use RWRP, so no 'free lunch' in the middle position.
Idiosyncratic? IIRC it's claimed that RWRP sounds different, lengthy forum debates...

Bye

 

[clintrubber]

Is there any way to get a regular single coil pickup to be hum free without resorting to splitting the coils and converting them to some form of humbucking configuration that changes the sound?

I overlooked this in the first post, sorry. For my understanding, you do indeed mean a split pickup like for instance on a P-bass? Could at least imagine it already results in a somewhat different sound due to the physical staggering of the two parts. There might be additional influences possibly changing the sound (I'm not intending to start such a debate, many forum pages on that exist already). Yet I'd say it'd be a small price to pay for getting hum-reduction.

But indeed it doesn't address the problem for single pickups.

Bye

 

[abbey road d enfer]

All the solutions that rely on a variant of humbucking, either split-coil, RWRP, "real" humbuckers, humbucking coil or shielding do not answer the issue of "vagrant" instruments.
ATM, I can see only two possibilities: getting rid of the interference source or using digital processing.
Now, as a DIYer, if I was sufficiently motivated, I could try designing a box including a sensor coil and a circuit that would substract it from the guitar signal. It could even be designed as not to interfere too much with the guitar's sound.
In fact that would be an externally mounted system similar to the MusicMan or the Ilitch Electronics.
Maybe someone could convince Ilitch to make a temporary-mounting version of his system. That would probably the most effective solution, since he has all the components already tried and tested.
The big difference between the MM and the Ilitch systems is that the MM uses a small low-Z coil, that would be easier to integrate, but it requires some gain in the electronics; I've never heard anyone complain about hiss issues, though.
There would be a probable issue with mounting the box to the guitar, taht would constitute a hindrance in live situations; in studio, I would think the pros largely compensate the cons.

 

[mhelin]

A split-coil Stratocaster pickup can be made so that it sounds just like a regular one but without the hum. Just use two 3-magnet bobbins and connect them in series and out of phase and stuck inside a regular pickup cover. Well, there might be some string bending issues, Fender with Super 55's uses some magnetic guides to help with blending the coils output when in between 3rd and 4th poles:

https://images.reverb.com/image/upload/s--1M3CA117--/a_exif,c_limit,e_unsharp_mask:80,f_auto,fl_progressive,g_south,h_620,q_90,w_620/v1405450376/sr3dniafozynb4heynwp.jpg

 

[Tubetec]

G+L do this one , Id meant to post this link earlier ,a few others have since mentioned it as well .

 

[mr coffee]

Differential wiring won't help much, as was covered above.

But there are humbucking single-coil sounding pickups that stack a humbucking coil under the regular coil. The best high impedance hum-cancelling ones (drop in a regular guitar) these days are the Dimarzio "Vintage" series IMHO.
They also look just like a regular Strat or Tele pickup, and installing them in the guitar will make most guitarists who get frustrated with the hum happier.

Or maybe he's OK just to have less hum with shielding and use a noise gate and "keep it vintage".