School me on the science, or witchcraft, of pickups.

[Maude]

I'm currently trying to choose a pair of pickups for a Hofner I'm doing and I've come across some points that, either I don't understand, or aren't really points at all. 

Essentially a pickup is magnet and a coil of wire, the string moves through the magnetic field and produces an ekectrical current in the coil, job done, yes? So does it matter whether the pickup is a bass or guitar pickup, other than physical dimensions?

The Seymour Duncan SM-1 & SM-3 mini humbuckers are, apparently, a good upgrade to the standard Hofner staple type pickups., but expensive. The Seymour Duncans appear to be Gibson Firebird replacements so designed for guitar. I think the toasters in Rickenbacker 4005 basses were just guitar pickups. 

So can I just find some cheaper minihumbers, or other style, that physically fit, and all will be good? 

What determines the tone of a pickup? Does the 'bassiness' come from the string gauge or the pickup? 

Sorry for all the questions but it would be an interesting discussion I think. 

🙂👍

[Al Krow]

Here's a useful intro note - hope it's not to basic.

Pickup types guide.pdf

[Maude]

That's a useful article but doesn't really cover what I'd like to know. 

I probably hit on to many points in one post to make much sense. I understand the differences placement and style of pickup makes so I'll concentrate on one topic for a minute. 

If I want a mini humbucker in one fixed position, what determines it's sound, ie magnet material, resistance, inductance, etc?

I should, within reason, be able to tell how a pickup will sound just by it's physical values shouldn't I? 

And if so what is it that those values reveal? 

I understand a bit like a higher resistance will lose some low end (?) but is inductance value (Henry) more important in estimating the output power? 

I'd like to understand this so that if I had the value of the original Hofner pickups, which were mini humbuckers, then I could compare replacements with some idea of what results any changes to these values would have on the tone. For example if the resistance and inductance were the same but the magnet material was different, what would the effect be, or if the magnet and resistance were the same but the inductance was different, what would be the result? 

I realise this is quite specialist but it would be good to know. 

[itu]

OK, this will be the theoretical part...

The wire is one part. It can be thick, thin, twisted... usually it is lacquered copper. The amount in the coil is related to the pickup's resistance (R). A short amount of wire equals low resistance and so on.

When the amount of wire is low, in theory the frequency response is wider and output lower. This depends on few other parameters, too, but is a very rough generalization. If the output is very low, the signal level can be amplified with an opamp (operational amplifier + a power source, like a battery; EMG), or the voltage can be raised by a transformer (Alumitone).

The coil has impedance (Z) and it changes over the frequency range. At 0 Hz, or DC, the Z is R.

A pickup is practically a low pass filter. Most of the pickups have limited response, and the output starts to go down after few kilohertz.

Coiling a pickup: yes, there are (stories of) magical hands, or machines, or makers, but the basic idea is to put some amount of a wire to a coil. There are also multi-coil pickups, please check https://www.herrickpickups.com/

Now we get to the basic principle: when the string (a conductive wire) is moving (vibrating) in a magnetic field, it produces small electric (AC) signal, which can be amplified in an... well, you know the rest. The power of the magnetic field, and the parametres of the coil affect the output - and the sound.

Magnetic material is actually a bit on a sidetrack. What is meaningful is the magnetic field (1 Tesla = 10 000 Gauss). Now it is so that the materials differ not only with each other but also within one "species". Because of this, a very weak neodymium could be weaker than a very strong ceramic. Neodymium is considered the strongest (i.e. the power/weight is the best so far) following by AlNiCo, Sm-Co, and ceramic.

Now we have the parts (wire, frame, magnet). The next step is to put them together. The ready set may be single, or multicoil, stacked, or a parallel humbucker... The sound comes out from a complete construction, where we have lots of parametres, but not a single will guarantee the end result.

A practical approach

If you are really into pickups, an LCR-meter would be very helpful. While I was working in a broadcasting company very long time ago, I had a chance to use a high end LCR-meter and measure my former Modulus Graphite Quantum's bartolinis. Very interesting, although expected results, by the way.

Prices of the meters are really high, though. There are single frequency units, but one f does not tell much about the overall response. As an example, this second hand Agilent costs over £1k and has only 6 static frequencies:

https://www.ebay.co.uk/itm/HP-Agilent-Keysight-4263B-LCR-Meter-100Hz-to-100kHz-RPG/253214470569?hash=item3af4c231a9:g:81AAAOSw6KVZhUTA

[Maude]

Thank you @itu.

Does the inductance (H) indicate the power of the output? Eg, a low R and high H pickup would, very generally speaking, have a thick bottom end with plenty of oomph. 

Also, is there any difference, other than string spacing or amount of pole pieces, between a guitar and bass pickup? Eg, if a pickup advertised as a guitar pickup had the same R and H values as the ones in my bass, then it should, in theory, sound alright. I don't want to say the same as different manufacturers etc sound different. 

I'm trying to find suitable pickups at a price I'm comfortable with and I've found two pairs with very different values and I'm just trying to get my head around what those different values will likely equate to. 

[itu]

1 minute ago, Maude said:

Does the inductance (H) indicate the power of the output? Eg, a low R and high H pickup...

Also, is there any difference, other than string spacing or amount of pole pieces, between a guitar and bass pickup?

Impedance, you should try to read this: https://en.wikipedia.org/wiki/Electrical_impedance

When a (bass, or g-word) pickup has different physical measurements, the electrical parametres may already change.

When the distances to strings is different, the output is different. It is possible to find similar pickups, but just looking at any single figure does not give you trusty answers.

[Maude]

I've found these pages which are quite interesting, and well explained for a non-electrically minded person like myself. 

I'm just trying to understand the basics as people seems to keep quoting the resistance figures of a pickup, but I'm increasingly reading that the inductance value is more important in estimating the performance of a pickup. 

I was hoping it would boil down to something simple like resistance value would indicate the brightness and inductance would indicate the power, in a similar pickup. Obviously everything else plays a part but it can't just be a wild stab in the dark, else a manufacturer wouldn't be able to custom wind a pickup to give the tone you ask of them. 

http://www.planetz.com/pickup-dc-resistance-and-output-levels/

 

https://www.planetz.com/pickup-inductance/#:~:text=Inductance is measured in Henrys,is DC resistance (DCR).

[itu]

I am very sorry. If single coil g-word pickups are mechanically similar (including magnets), the DCR may be the factor that describes the many differences somewhat. Other than that, no one can reduce sound quality parameter matrix to a single number or word:

"How did the band sound?" "56.3!"

(Here the number 56.3 equals the word "round".)

A new variable frequency professional LCR-meter seems to cost around £10k. Ouch. But an ebay unit "ET4501" and its variations (ET4502, ET4510) seem nearly affordable. Interesting.

[Woodinblack]

12 hours ago, Maude said:

I'm just trying to understand the basics as people seems to keep quoting the resistance figures of a pickup, but I'm increasingly reading that the inductance value is more important in estimating the performance of a pickup. 

Thats because it is much easier for most people with commonly available equipment to measure resistance. Same with speakers.

Also there is one important measurement - a pickup with a resistance of either zero or really high is broken!

[Baloney Balderdash]

Induction.

The fact that movement of a magnetic field will create a respective electrical current, and the other way around for that matter.

Very basically. 

Edited December 21, 2020 by Baloney Balderdash