rewinding pickups

[sgt mukuzi]

relax, its only a ripper


i knew my theory would get this thread rolling. how about some aluminum magnets from tonesRusa

[snitchez]

yeah, its only a ripper. not a 60s jazz bass. =)
im thinking of selling it. hence getting everything sorted out. everything on the bass is original and with its smelly hardcase too. but ash is the man that fullfills my desires... its true... no matter how wrong it sounds. =)

this is a perfect example!

[Ears]

And yet you can charge alnico, measure its gauss, stick it on the fridge for a week and see the measured gauss has dropped by 10%. Thats exactly what some of the boutique pickup makers do to 'age' their magnets. When you order charged alnico magnets you can usually bump the gauss up 5-10% straight away by recharging them. They'll drop back down eventually. How fast depends on the external loading.

Yes, newly and strongly magnetised AlNiCo will demagnetise to a certain extent until point of stability is reached.
This settling period can be accelerated by temperature manipulation and exposure to weak fields and according to some magnet manufacturers deliberate partial demagnetisation can even reduce or eliminate susceptibility to stray magnetic fields. I'm unsure if placing on a fridge accelerates the process or if simply the effect you observe is this natural settling process.
A brief check on the net (according to
http://www.eamagnetics.com/gen_faq.asp# ... agnet_last )
once stable, on its own and away from strong magnetic and electrical fields general magnetic strength of permanant magnets will change in the order of 1% per decade. This figure is in agreement with other data I've read before on AlNiCo specifically.
Maybe the electric fields generated by the PUp accelerate magnetic degradation, I'm unsure, are the fields strong enough? Anyway I suspect it's marginal and not going to cause noticeable falls in general output level.

[B45-12]

Might be fun too as I seem to recall some of the Gibson pups from the 70's were potted in epoxy - think the pups on the L6 were and I know they replaced the ones on my SG under warranty rather than mess with them (covers were corroding madly) - anyone know 4 certain Ash, Ears? etc.

[Ears]

Made a discovery just this morning that alnico 5 (and alnico 8 ) is 'anisotropic' and prefers to be magnetised in a particular direction of polarity.

So maybe, beware of non premagnetised pole pieces such as sold by Stewmacs, as you won't be able to tell which way is best?? Guitarparts sell pre-magnetised ones so it's no issue, if it is an issue at all. I'm Interested if Ash has insight on this? is it a potential problem?

It IS fun to wind your own but making a decent winder and a counter can be a bother. I wound mine because I wanted custom pole stagger and spacing and custom flatwork. But I imagine its much easier to engage services of Ash if these sorts of issues aren't concerns (or even if they are!).

[ash]

Most HB bar magnets are supplied premagnetised anyway. If they're not and it matters they will specify the intended magnetic axis. Most makers prefer unmagnetised slug magnets as it makes the bobbins easier to assemble and you can't rely on premagnetised slugs to be consistent. They seem to prefer being charged in-situ.

[snitchez]

im officially lost. pups have always been my weakness in the bass/guitars section. =(
i guess im gonna be learning some new stuff!

[calling card]

It's ok snitchez, this is pickup forensics, anyway I'm bored.
Whats the approx range of voltage & amp output from a guitar pickup?, think I'll go plug the multimeter in later.

[Capt. Black]

Maaan, any time the conversation here starts to get too technical/esoteric/over-my-head I just try turning up the volume. That seems to fix everything.

[Ears]

It's ok snitchez, this is pickup forensics, anyway I'm bored.
Whats the approx range of voltage & amp output from a guitar pickup?, think I'll go plug the multimeter in later.

According to DiMarzio site, it's pup range from about 100mV to over 500mV. The site neglects to say if that's RMS, peak, or peak to peak.
Author of Valvewizard.co.uk informed me: "- I usually assume 250mVrms for single coils, 500mV for humbuckers and 1V for highoutput types" So about 12dB variation.

[calling card]

Thanks Ears, so thats 0.25v from a single coil, there's the ohms law thing applies to coil winding from memory. More windings = higher volts/less amps, less windings lower volts/more amps.

[ash]

According to DiMarzio site, it's pup range from about 100mV to over 500mV. The site neglects to say if that's RMS, peak, or peak to peak.
Author of Valvewizard.co.uk informed me: "- I usually assume 250mVrms for single coils, 500mV for humbuckers and 1V for highoutput types" So about 12dB variation.

If I recall correctly, DiMarzio's output figures are derived from a machine plucking the A string at some defined rate, height, gauge etc. I think its peak to peak.

[Ears]

Thanks Ears, so thats 0.25v from a single coil, there's the ohms law thing applies to coil winding from memory. More windings = higher volts/less amps, less windings lower volts/more amps.

Sort of, the PUp can be thought of as a voltage generator with internal impedance in series with it.
More windings means greater voltage can be generated but also means higher internal impedance in the PUp (which is inductive and resistive and to certain extent capacitive).
The current drawn from the unit is a function of the PUp's capability as a voltage generator AND also dependant on what's connected to it as a load. A light load will draw higher current from the PUp but because this current is pulled through the pUp's own internal impedance (lets call it its resistance) a portion of the generated voltage is dropped across it internally, resulting in average voltage output as seen at the terminals of the Pup falling. The more current is pulled from it the more energy is wasted inside the PUp. This also has consequences for the tone produced.

Rule of thumb is that it is best not to "load" or pull too much current from the PUp. Use pots 250K or above.
The higher the internal resistance of the PUp the more voltage can be lost internally across it, that is why humbuckers, having about twice the resitance of single coils, benefit from seeing higher valued loads (500K pots) at their terminals. That is, the higher value of load results in less current drawn from the pickup and less voltage dropped internally.

Because as more windings (= higher output voltage capacity) are added it means the internal resistance rises, the manufacturers supply a figure for the internal resistance. It's a crude measure of relative PUp output, not a good measure at all but one we live with because it's been around for so long.

[Post edited for clarity]

[Ears]

According to DiMarzio site, it's pup range from about 100mV to over 500mV. The site neglects to say if that's RMS, peak, or peak to peak.
Author of Valvewizard.co.uk informed me: "- I usually assume 250mVrms for single coils, 500mV for humbuckers and 1V for highoutput types" So about 12dB variation.

If I recall correctly, DiMarzio's output figures are derived from a machine plucking the A string at some defined rate, height, gauge etc. I think its peak to peak.

Thanks, I wish that sort of info was standard across the industry. Despite their excellent intention, marks off the De Marzio website for supplying tech info without clearly defining the measurement. It provides a very good comparative guide though.

[calling card]

Cool, I'm starting to put the pieces together. Excuse my ignorance, so a volume pot when turned all the way down is infinite resistance & when full open regulated to 250k or 500k which would keep the pickup 'hot'.