How to wire one-per-string magnetic pick-ups

[poldus]

Hi, I have built a five string electric upright bass and bought the magnetic pickups used in NS basses. I have a Bartolini preamp to buffer and mix the signal from these and a piezo installed on the bridge.
Three pick-ups are labeled positive, two are negative and one is a null. Here is the description from the seller's site:

The EMG 5SW is a magnetic pickup system designed for Electric Upright Bass. The system was initially designed for Ned Steinberger and is used on NS CR and EU instruments. Price is per set of 6 pieces, made by EMG, cables with in-built connectors, set made of 3 pcs of positive pickup, 2 pcs of negative pickup, 1 pc of null pickup

Should I wire them in series like this:
POS-NEG-POS-NEG-POS-NULL ?

 

[weltersys]

Should I wire them in series like this:
POS-NEG-POS-NEG-POS-NULL ?

Poldus,

Seems information about single string pickup wiring is not widely shared, could not find any reference to a "null" pickup.
Alternating winding directions on every other string does seem likely to be the best for common mode noise reduction, "hum bucking".
That said, checking noise in the field of a noise/hum source, like a loaded 12v/120v light transformer, "wall wart", switching power supply or the like would be informative- could be there is better noise reduction with the two "NEG" on the outside "B and "G" strings.

Whether the pickups are in a straight line, or staggered towards the bridge or fretboard every other string would also be a consideration affecting both string separation and noise cancellation, as well as harmonic content.

My personal inclination would be parallel wiring rather than series, primarily as a loss of one pickup would kill all output, rather than loosing one string only.
Parallel wiring could also allow individual equalization adjustment for each string.

I'll be interested in hearing what you decide to do, or if you do find out how the NS EU bass is actually wired.

Cheers,
Art

 

[JonSnell Electronic]

Most manufacturers use piezo cells for individual strings wired in parallel.
I built a pickup system for a Telecaster guitar, a few years ago. All coils were on independent magnets and I wired them in parallel as I used 950turns of 42guage enamelled copper wire for each one. That gave a good sound and a reasonable impedance.
I experimented with series wiring but that just gives hum as the pickups get nearer the signal wire.
In phase and out of phase would give you an odd sound that some guitarists like.

 

[JMFahey]

I would write EMG!!!!!!
And then post answer here, to help fellow members who might have the same doubt.

I find it weird they offer 5 "working" pickups and a "null one .... while traditional Acoustic Bass is 4 string.
How did you* intend* to mount them?

I *think* you use 2 positive and 2 negative ones ,one per string, in a 4 string Bass, so hum cancels.

All in parallel, of course.

I *guess* you use all 5 active ones in a 5 string Bass (is there such a thing?) and then use the 6th one, mounted somewhere nearby but under no oarticular string, to balance Hum out, similar to Alembic´s famous "mystery 3rd pickup"

But this needs confirmation ... specially before you drill your precious Bass

 

[poldus]

Great info, thank you guys, I will try parallel first and will post my findings next week.
Yes, the null pickup is meant to be hidden away but is supposed to serve a purpose in the circuit.

Regards

 

[Printer2]

If you put them in series there is no advantage over a regular pickup. The null pickip is the humbucker. Whether that one is parallel or in series? Five string basses have been around for a long time.

 

[Markw4]

Looks like the 5SW is for a five string bass. There is also a 4SW for four strings.

Seems likely the + and - ones are likely meant for alternate strings to get some humbucking effect. The null pickup may be to help null out any remaining stray magnetic field pickup.

How they get wired may depend on what the user wants to do. For example, the magnetic individual string pickups commonly used for MIDI sensing have low-power opamp buffers, one per string, located very close to the pickup. A mixer circuit could be used after that to balance out sensitivity for each string. Or not.

 

[mondogenerator]

I would (being crazy as I am) install one switch per string for phasing.

Then I would have another switch per string for parallel (humcancelling) and one for series (humbucking) action, depending on phase switch preceding

These could be pull shaft pots, one per string

Dont ask for schematic as I havent worked out one yet...

But that's what I would do, for ultimate flexibility, almost like a Fender Jaguar/JagStang but bass.
It may be that only 3 or so combos ever get used, much like Brian May and his guitar preferences.

I would do it this way purely for the sake of it, speaking as the son of a luthier that cloned a Strat at 16, wound his own pups, and ran them continuously from bridge to neck. Total probably about 10 pickups

So yeah,

5 push pull pots, wired for volume of each string, pull to change phase, then an additional series parallel switch per string.

Would be quite a feast on the eyes! The Null PUP is new to me, not being a bassist, but it should be out of phase. Whether series of parallel is largely irrelevant IMHO, both connections cancel hum.

 

[weltersys]

I would (being crazy as I am) install one switch per string for phasing.

It may be that only 3 or so combos ever get used, much like Brian May and his guitar preferences.

Whether series of parallel is largely irrelevant IMHO, both connections cancel hum.

Mondogenerator,

I am a fan of polarity reversal for the variety of tone it imparts with two pickups that pick up the same string, as in the guitar examples you mention. The reverse polarity "out of phase" settings largely cancel low frequencies, and create distinctive peaks and dips in the response.

However, with a single pickup per string, the effect of reversing polarity would impart virtually no change in tone, as the adjacent string output is too little to affect the phase of their combined output. If you happened to reverse the polarity of only the two already reversed ("NEG") pickups, much of the common mode noise ("hum") cancellation would be eliminated.

Below is a screen shot from Ubertar Pickups illustrating how little output from adjacent strings is picked up by the individual strings, I'd expect the separation from the EMG 5SW pickups to be similar.

Art

 

[mondogenerator]

Hi Art,

I have never used a single string pickup, and you clearly have - so if you reckon phase reversal between strings is largely pointless, I cannot argue.

I imagined adjacent string *stray* pickup would be greater - but Thinking again, perhaps they would be designed to have every compact field around the string, if the end use is likely MIDI triggering.

I hadn't considered that.

So..

Depending on the individual coil resistance/impedance, and guessing each pickup is about 2k, all would go in series, in phase.

The Null coil would probably go in out of phase, in series too, if it's essentially the same coil impedance.

I'd still install a phase switch for the Null coil, just in case it has been wound in the reverse direction to the normal pickups and is meant to be installed, in phase.

 

[Gnobuddy]

I imagined adjacent string *stray* pickup would be greater - but Thinking again, perhaps they would be designed to have a very compact field around the string

I've read a couple of research papers that modelled the magnetic field around a guitar pickup. The field is relatively uniform across the diameter of the actual polepiece, and falls away very rapidly in all directions from there, both laterally (parallel to the plane of the guitar top), and in the direction of the polepiece axis (perpendicular to the guitar top face.)

One of the unexpected side effects of this is that lateral vibration of the guitar string - in the same plane as the guitar top - generates negligible output signal from the pickup! This is because the string is moving in a region of constant magnetic field (which extends the full diameter of the pole piece), so there is minimal flux change, and therefore, minimal induced EMF in the pickup coil(s).

Vibration in the vertical plane - perpendicular to the guitar top - on the other hand, moves the guitar string through a region where the magnetic field strength varies rapidly (and nonlinearly), so this generates a heavily distorted EMF from the pickup coils.

This heavy waveform distortion inherent in the design of the conventional magnetic guitar pickup itself is one of the primary reasons why electric guitars sound so very different from acoustic ones (the sound is harsher), and why piezo pickups have come to be favoured in the majority of electro-acoustic guitars (piezos don't produce the same type of distortion, so the sound is closer to the sound of the vibrating string itself.)

In practice, the picked string vibrates and wiggles in both planes after the pickup loses contact with it, so there is always a sizable component of of motion in the vertical plane, and therefore, plenty of output from the magnetic pickup, no matter what your string-picking motion might be.

Since reading those papers, I've modified my guitar picking motion in a way that produces a larger vertical component of vibration. I didn't notice any change in pickup output, but I found other benefits, so I've retained the technique.


-Gnobuddy

 

[Printer2]

This heavy waveform distortion inherent in the design of the conventional magnetic guitar pickup itself is one of the primary reasons why electric guitars sound so very different from acoustic ones (the sound is harsher), and why piezo pickups have come to be favoured in the majority of electro-acoustic guitars (piezos don't produce the same type of distortion, so the sound is closer to the sound of the vibrating string itself.)

I think the piezo is more popular because you don't have this pickup in your soundhole but tucked away out of sight under a saddle. Until not all that recently piezo pickups were not held in much regard for accurate acoustic guitar reproduction.

 

[Gnobuddy]

Until not all that recently piezo pickups were not held in much regard for accurate acoustic guitar reproduction.

Agreed, and certainly there have been plenty of nasty-sounding piezo pickups over the years. But magnetic pickups sound even less like an acoustic guitar to my ears. They may not have the same stinging excess treble (good), but they also have lots of harmonic distortion and that harsh electric-guitar sound (bad if you're trying to sound like an acoustic guitar).

With a piezo, applying some carefully considered EQ usually makes a big improvement. Craig Anderton's article on the subject is very good. Even just low-passing the guitar to roll off frequencies above, say, 4 kHz helps the sound a lot.

With a magnetic pickup (on an acoustic guitar), I found that increasing the pickup height as much as possible helps. The magnetic field varies in its most nonlinear way immediately above the pole pieces. If you move a centimetre away, the field varies more slowly, so there seems to be less waveform distortion if the guitar strings move through it. But it still sounds like an electric guitar, not an acoustic guitar, which I think means there's still lots of harmonic distortion.

Taylor is one company that seems to have gone back and forth between piezo and electromagnetic pickups on their acoustic-electric guitars. They keep re-designing first one, and then the other (they created a very differently designed pizeo saddle pickup a few years ago), and switching production to the latest and greatest version. Clearly somebody high up in the company is dissatisfied with the sound of both types of pickups.


-Gnobuddy

 

[mondogenerator]

Gnobuddy,

Didn't you ever lower the action on a guitar as far as possible, and jack the pickups as high as possible to increase the output? in my case I lowered the action on a clone Strat with worn frets, so it had that bluesy feet rattle.

Or stick the slack, new string to the pole piece, changing a string with the amp still on? Ok that's one for the Airheads, and isnt advisable

I learnt at a very early stage in my guitar playing, way before I really understood anything electronic, that the pickup output was far higher in the axial plane than in a radial, longitudinal vs transverse, vertical vs parallel to the body.

It amazed me that they worked at all (pickups)

Now I'm older, and I hope wiser, I'd imagine the string displacement begins at pluck, in radial motion both parallel to the body and along the string. I'd guess it then degrades to an orbit about the string centre line.

It would probably be easy for me to check, if I search for slow mo string motion videos - so I'm off to do that!

 

[Printer2]

Which do you like better?


YouTube

 

[Gnobuddy]

Didn't you ever lower the action on a guitar as far as possible, and jack the pickups as high as possible to increase the output?

Sure, but I didn't do the equivalent experiment in the other plane - I didn't pop the nut out of its slot, slide it sideways, and see what happened to the output from the appropriate "E" string. So I had no basis for comparing the effect of vertical string displacement versus horizontal string displacement.

It amazed me that they worked at all (pickups)

I've always visualized them as a variable reluctance magnetic circuit, with a DC polarizing field (from the magnet), and a coil to pick up the resulting changes in magnetic flux.

When I saw the amount of distortion conventional magnetic pickups create, I thought about using 7 pole pieces (rather than 6), with the strings led half-way between each pair of pole pieces, rather than directly over them. Invert the direction of magnetization of every other pole piece, and you now have a magnetic field gradient that's linear to first-order halfway between the pole-pieces; this should create far less harmonic distortion in the output. You'd also need one coil per pole-piece, wired in alternating polarizations, to avoid cancelling out the signal between adjacent pole-pieces.

I don't know if this has ever been done for six-string guitar, but it appears that Leonidas Fender might have tried something like this on an experimental bass guitar - a five-pole pickup, poles spaced halfway between the strings. Reportedly it did produce a different sound, but the idea didn't go into production in any Fender bass. I turned up some evidence that it might have made it to production in a MusicMan bass, but can't find that link now.

It would probably be easy for me to check, if I search for slow mo string motion videos - so I'm off to do that!

Watch out for the ones that show low frame rate artifacts (aliasing) rather than actual string motion. There are lots of these out there, usually filmed with somebody's phone.

Considering the thickest open string vibrates at 83 Hz, the camera needs a frame rate above 166 Hz to avoid aliasing even the very lowest note on the instrument. It's going to take a proper - and very expensive - high speed camera of the sort used for ultra slow motion shots to do this properly!


-Gnobuddy

 

[Gnobuddy]

Which do you like better?
YouTube

To me, the magnetic pickup in the demo sounds like an electric guitar, and not even remotely like an acoustic guitar. It also produced thin bass and too much treble. But it is the harshness in the timbre (lots of harmonic distortion in the waveform from the magnetic pickup) that makes it sound like an electric guitar.

I thought the piezo pickup was also too bright, and IMO it would benefit from some treble-cut. But I don't hear the same sort of harsh THD as the magnetic pickup. The bass sounded warmer to me as well, i.e. it was better balanced with the midrange than in the case of the magnetic pickup.

I would have really liked to hear a flat-response condenser mic placed in front of the guitar as a reference sound, so we could compare both piezo and magnetic pickups against it. Without that, we're only comparing one fairly nasty sound with a second fairly nasty sound.


-Gnobuddy

 

[Gnobuddy]

With a magnetic pickup (on an acoustic guitar), I found that increasing the pickup height as much as possible helps.

I just noticed that I made a very bad typo in that post - I meant to write exactly the opposite, i.e., the magnetic pickup sounds less-bad on an acoustic-electric guitar if you decrease the pickup height as much as possible, so that the guitar strings are as far above it as possible, where the magnetic field falls away more linearly.

Sorry for the typo!


-Gnobuddy

 

[mondogenerator]

I use a fairly cheap piezo, one of these:

Dean Markley Sweet Spot

Dean Markley Sweet Spot Pickup - Under-the-saddle bridge guitar pickup

It's a great add on piezo, good sound into the right load (not so good on my valve head)

On the pick up topic, pole pieces etc, I often thought the reasoning behind Hot Rails was to create a more uniform field over the strings, in a similar way to 7 poles over 6 strings.

I still have some small pieces of chromed plate, and magnet, somewhere....I was going to try winding a pickup and never got around to it

0.15/0.18mm wire is probably too thick though! Shame, I have a few miles of it!

 

[mondogenerator]

I use a fairly cheap piezo, one of these:

Dean Markley Sweet Spot

Dean Markley Sweet Spot Pickup - Under-the-saddle bridge guitar pickup

It's a great add on piezo, good sound into the right load (not so good on my valve head)

On the pick up topic, pole pieces etc, I often thought the reasoning behind Hot Rails was to create a more uniform field over the strings, in a similar way to 7 poles over 6 strings.