magnet theory

[walters]

electromagnetic theory and practice and a book on basic transducer theory yes i do need a book on this stuff sorry guys

Walters, WHY are you asking these questions?
Sorry i'm trying to build a guitar pickup and to understand more about
electromagnetic and transducer theory my electronic class didn't really
teach me that much about it so im really bad at it can u guys help me out with these questions so i can advance myself.

Sorry for me it helps me out just talking about it with u guys and then when i read the book im not so scared and it soaks in better when u guys talk to me about it

 

[walters]

Yes any arbitrary phase out of the variable reluctance transducer formed by the magnet, coil, and guitar string (although you can do phase-shifting in circuitry external to the transducer),

Yes im trying to get more arbitrary phase degrees out of a guitar pickup
can u please help me . What kind of external phase network would do the trick to get between 0-180 or more?

change the pickup coil properties, wouldnt it be easier just to add something after the pickup output to change its phase?

Do u guys know whey the pickup coil properties are only zero and 180 degrees?

 

[Styx]

Walters I think you are really getting confused abt phase here


PHase is a shift in time.

The 180deg phase-shift you are talking abt is due to swapping pickup terminals over (+VE to -VE). Now yes this does result in a 180deg phase-shift for a sinewave (kind of) BUT it isnt really it is just an inversion

Why I here you say? Well there is no timeshift in swapping terminals over is there?

A 180deg phaseshift on a PURE SINEWAVE is indistiguashable from an inversion. However for an arbitary waveform an inversion most definitly is NOT a 180deg phase-shift.

Yes soundwave do repeat (and are complex in shape) so this inversion ~ phase-shift can be viewed as valid BUT it is not a true phase-shift since no time-delay has occured



To truely phase-shifts it you would either need to do it in digital and just delay a sample, but against what fundemental? THIS simple fact makes what you want completely pointless (so please stop this futile investigation)

You could do it analogally BUT again time-shift against what fundemental (since the fundemental will keep changing)


NOw IF you wanted to do it you could at the coils take advantage of electromagetism to its fullest and rather then having the pickup coil going to an amp, make it part of a phase-shifting auto-transformer (the kind used to creat multi-pulse rectifiers for lower ThD of current)

THIS allows you to phase-shift (fixed ONLY) a pre-set degree. BUT it would phase-shift ALL freq and thus it would result in just a lag (a very slight, not even human detectible) lag between plucking and hearing...

Basically POINTLESS



As to Eddy current. As you know current flowing through a cable will create a magentic field around it (you do know this dont you?)

Right well it is true the other way around (its how transformers and machine work). A magnetic field can induce a current to flow.

For magnetism to induce current to flow it really needs to be an AC magnetic field. This is When Lenz's law comes into play

Lenz's law:The induced emf generates a current that sets up a magnetic field which acts to oppose the change in magnetic flux.

good old nature wants to stop what you want to do. That induce current will produce its own magnetic field that will oppose the magnetic field you are creating.

However, if you setup this current in an iron block (ie a magnet or in the stator of a machine) it will heat it up due to copper-losses and it will get bloody hot and the efficency is shite


That is why Trasformers and Electrical machines have laminated magentic cores, to minimise this eddy current

 

[walters]

THanks alot for the information

phase-shifting auto-transformer- will this give me all the phases between 0-180?

So when flip the guitar pickup terminals its a inversion?

Whats the difference between a Inversion and 180 degrees?

Eddy current? are u saying that eddy current is the magnetic field and flux current?

Regular current is from voltage but eddy current is from magnetic fields and flux?

 

[Styx]

THanks alot for the information

phase-shifting auto-transformer- will this give me all the phases between 0-180?

BUT why would you want that since you would NOT hear it!!!!!!!
EXplain why IF you want help

So when flip the guitar pickup terminals its a inversion?


Whats the difference between a Inversion and 180 degrees?

Have a look at my picture, can you tell the difference, there is a difference but can you tell?

Eddy current? are u saying that eddy current is the magnetic field and flux current?

Regular current is from voltage but eddy current is from magnetic fields and flux?

NO !!!!!!!!!! FFS
I am saying a magnetic flux will INDUCE a current in the material the flux is flowing through. THIS current is known as eddy current (due to their pattern, similar to eddy currents when talking abt water)

Eddy current is an unwanted side-effect of varying flux.

YES a battery will generate current, but so will magnetic ccts, that is how generators work and how transformers work.

Battery's produce DC-current, while magnetic cct produce AC current

 

[walters]

Thanks for the help

So eddy current is the Induced current from the magnetic field and flux

phase-shifting auto-transformer- will this give me all the phases between 0-180? BUT why would you want that since you would NOT hear it!!!!!!!
EXplain why IF you want help

Yes you can hear it when u have 2 pickups on if one pickup is zero degrees and the other pickup is 20 or 60 or 180 degrees they cancel out frequency so u can hear it big time


So when flip the guitar pickup terminals its a inversion?

Whats the difference between a Inversion and 180 degrees?

Have a look at my picture, can you tell the difference, there is a difference but can you tell?

DO u have a pictures of the difference of a inversions VS 180 degrees?

If a Inversion is not Time degrees then what is a magnetic inversion?

 

[walters]

Thanks alot for the pictures

From the pictures the magnetic inversion looks the same as the phase degrees whats the difference please?


It seems that the inversion is a "Polarity" not phase but polarity were the phase is a frequency based on phase degrees

 

[audioguru]

I think Walters is talking about the "comb filter effect" of having two pickups with different phase. The different phase is created by staggering the pickups (I guess, I'm not a mechanic).
Guitar makers don't know electronics so they make electronic filters mechanically.

I think if you want a comb filter effect then make and use an electronic comb filter. I would use an allpass filter plus an adder, a balanced modulator IC or a digital delay line. A guitar maker would just spin a Leslie speaker faster and faster until it blows apart.

 

[walters]

comb filter effect" of having two pickups with different phase

Yes i am but i can only get zero and 180 degrees mechanically or magnetic. I'm trying to get between 0-180 so i can have a variable comb filter effect

 

[walters]

A guitar pickup has a resonance frequency and a Q which is based on the LCR the wire,gauge of wire, magnet forming the LCR.How do i make the resonance frequency variable?

I'm trying to get a adjustable Q, adjustable Q width, Adjustable Q depth?

 

[bryan1]

Eh Walters a quick google search picked up a heap of info that you need so get off ya butt and use the internet for your own research and stop wasting everybodies time with stupid irrelevent questions. Out of the 400 odd posts you've done probably 1 or 2 of them would be a valid question but the rest is just garbage. By the way do you know how much to charge for those fries yet :?:

 

[audioguru]

comb filter effect" of having two pickups with different phase

Yes i am but i can only get zero and 180 degrees mechanically or magnetic. I'm trying to get between 0-180 so i can have a variable comb filter effect

Stagger the pickups to make a mechanical delay. One pickup gets disurbed by the string before the other, creating a delay which makes a phase difference between them. Then mix their outputs in a mixer. An electronic mixer, not a food mixer. :lol:

 

[walters]

how would i Stagger the pickups or u mean offset the pickups ?

 

[audioguru]

A guitar pickup has a resonance frequency and a Q which is based on the LCR the wire,gauge of wire, magnet forming the LCR.How do i make the resonance frequency variable?

I'm trying to get a adjustable Q, adjustable Q width, Adjustable Q depth?

I haven't tried it but I think the inductance of a guitar pickup is too low to make a good tuned circuit. Change the capacitor in parallel with it to change the peak's frequency. Load it down with a resistor in parallel (its load) to reduce the Q and use a very high value resistor as its load for its max Q or rewind it for a higher Q.

Or build an electronic parametric filter for everything you want and more.

 

[audioguru]

how would i Stagger the pickups or u mean offset the pickups ?

I don't have a guitar, never had one. Ask a guitar geek.

 

[walters]

Thanks alot for the information

Change the capacitor in parallel with it to change the peak's frequency.

This would change the Q frequencys but what about the "width" of the Q?

How do i rewind a pickup to have a higher Q? would change the magnet or more windings?

 

[audioguru]

Read up about and understand a tuned circuit's Q. It is very much related to badwidth, oops I mean bandwidth.

You could mechanically re-wind the coil over and over and still not get what you want, or you can make an electronic filter that you adjust with knobs or a pc.

 

[walters]

Thanks for the help

How can i get a variable magnetic phase from 0-180?

My guitar has 2 pickups one is inphase the other pickup is out of phase

The out of phase pickup i just flip the wires the hot and ground and it reverses the polarity. The 2 pickup are suppost to be 180 degrees out of phase but im trying to get inbetween 0-180. You thought about a variable transformer that would change the polarity from 10 degrees to 170 degrees

It seem that a magnet is Fixed for only zero or 180 degree why i don't know but i'm trying to get between these degrees

 

[audioguru]

My guitar has 2 pickups one is inphase the other pickup is out of phase

Then if you add them they cancel and the output is zero.

It seem that a magnet is Fixed for only zero or 180 degree why i don't know but i'm trying to get between these degrees

Because you want the comb filter effect. Mechanically, by staggering the pickups. Or electronically with a circuit.

Maybe you should study effects circuits for guitars. Sweeping the frequencies of a comb filter or flanging sounds cool. It would nearly be impossible to sweep them mechanically.

 

[walters]

The guitar Pickup has a LCR internal from the magnet,coil of wire
by coil tapping the LCR goes non-linear

example the coil of wire turns= 8000 turns
coil tap the wire turns to 6500 turns
the LCR- non-linear

If one pickup is "in phase"(zero degrees) and the 2nd pickup is "out of phase"(180 degrees) i need a circuit or a transformer that would adjust the pickup to go "in phase to out of phase variable" so the pickup can go inphase zero degrees , 10 degrees,20 degrees, 30 degrees, 40 degrees, etc. until its out of phase

If the out of phase pickup is 180 degrees at 8000 turns would it be output of phase 180 degress at 6500 turns "coil tapped"?