homemade pickups, custom preamp

[DiggyFresh]

Not sure if it's the right place to talk about this but i'm sure it can be of interest to some!

i've been toying around building home made megnetic pickup transducers,  With strong magnets and magnet wire.
i use thos experimental pickups to amplify weird things and experiment, like weird metal strings, chromaharp, springs and even toyboxes.

they work, but i always run in a problem when i try to amplify the signal, i use a mic preamp's DI input (api 512c).
I get a sound but it's low, i need to max the gain and of course its super noisy...


probably an impedance problem but im not super knowledgable in that field.



anyone knows about how i could measure the impedance of my pickups and build small preamps optimized for the pickup?
Can i get an idea just by measuring the resistance of the pickup?


if anybody wants more info on the pickups feel free to ask.



Example:  I built a "Mini" Fender rhodes piano using a chinese toy piano wich had metal tines as sound source,  i bought a few rhodes pickups for cheap on
the net, wired them like the rhodes but it doesnt seem to have the correct impedance for my preamp, volume a little too low and effects pedal don't work as intended.


these things are fun to experiment and a lot of weird sounds can be made with em! try it out!

Thanks! 

[Mark Hammer]

1) A much better place / meilleur endroit to ask these questions is the pickup makers forum, here:  http://music-electronics-forum.com/f11/

2) Measuring DC resistance on pickups is easy.  Measuring "impedance" is harder, and requires moe than a simple multi-meter.

3) What wire, what magnets, and how many turns?  A weaker pickup will require more amplification, and more amplification will risk more noise.

[defaced]

1) A much better place / meilleur endroit to ask these questions is the pickup makers forum, here:  http://music-electronics-forum.com/f11/

+1000  The guys over there really know their stuff. 

[DiggyFresh]

 thanks for the reply and the link Mark! i'll investigate!


Yes impedance is still a very mysterious field for me, i'll try to look it up.



Most of the pickups are very experimental,  I have some 45 size magnet wire (pretty small).  i dont realy remember the # of turns and so far i've
used a bunch of different strong magnets.

i just measured the dc resistance on one of them, roughly 46 ohm.

I know by experimentation that the stronger the magnet,  stronger the volume, and the more wire turns, more volume also.
( but i think i saw way back that too many turn might have negative effects...)

im thinking of experimenting with Neodium magnets next, i should get a way greater output!


So should i just add more turns and add stronger magnets and try to do a decent low noise preamp that would be fit for guitars ?




P.s   Mark, if you are THE Mark Hammer, i own several of your Lp's and love your soundtracks!  feeling honored! And anyways thank you very much for
your contributions to this forum!

[Kesh]

I wound a few picckups before getting into effects.

Some guidelines that cover all types and shapes.

Magnet wire is 42 awg or damn close to it.

Winds number 4000 - 12000. For split coils like humbuckers or precision basses, that is per coil.

DC resistance (just hooked up to a mutlimeter) is maybe 5k to 25k.

[DiggyFresh]

thanks alot Kesh! That's a great starting point for me!

i have 45 magnet wire, so i guess i'll do a little more turns?  (cause the wire is smaller?)


and judging by your Dc resistance figures, i guess i should do Way more turns as i was closer to 50 ohm than 5000 ohm.


Thanks for the great info!  and that other forum is a gold mine for ideas!  I'll register as soon as i have some time!

John

[Kesh]

i'm guessing by your 46 ohms of 45 wire you have maybe 15 feet of wire on there. A typical bass pickup has maybe 5000 feet.

This is how I did it

[Seljer]

thanks alot Kesh! That's a great starting point for me!

i have 45 magnet wire, so i guess i'll do a little more turns?  (cause the wire is smaller?)


and judging by your Dc resistance figures, i guess i should do Way more turns as i was closer to 50 ohm than 5000 ohm.


Thanks for the great info!  and that other forum is a gold mine for ideas!  I'll register as soon as i have some time!

John

Yep, way more turns. Like mentioned, a typical guitar pickup has a couple of thousand turns of wire. The amplitude of the voltage you get is mainly dependant on just the number of turns.

The thickness of the wire affects the DC resistance, which affects the sound indirectly, but also the shape of the coil (you can wind a smaller coil with the same number of turns with thinner wire which leads to less inductance, etc...)

[J0K3RX]

Stewmac has some good kits... you can make your own winder

http://www.stewmac.com/shop/Electronics,_pickups.html

[Kesh]

Just to add, super strong magnets are not necessary. Too strong magnets distort a guitar's sound by pulling the string off its usual waveform. Normal solution is to move pickup further away from string.

The standard magnet in classic pickups is Alnico, which is weaker than ceramic, and much weaker that neodymium.

[artifus]

i've been tinkering with this recently using inductors and magnets with surprisingly good results - i was actually planning to post about it once i'd got it together to record some sound samples but now is a good as time as any: http://www.diystompboxes.com/smfforum/index.php?topic=98772.0

[DiggyFresh]

Thanks alot guys! great info! 


@Kesh   yep, i probably had not too much wire on it, winding was kinda painfull as i used an old turntable wich can do 78rpms..  (haha)

the drill thing is a good idea, i thought about it, i'm just not sure how i would feed the wire from the spool with a reliable system without breaking
the wire (45 gauge is pretty slim and easily breakable, Pain)  Do you have pics of how you fed the wire to the drill ?? 


@Sejler   Can you give me more info about how the dc resistance affects the sound?  i'm guessing thicker wire= less dc resistance ??  is that a good thing ?
              (except that it would be bigger)   And you say same number of turns with smaller wire = less inductance   do you mean less signal inducted from the magnet
              in the wire ??  So less amplitude of signal ??    So thinnier wire would need more turns to have the same amplitude ? realy great info for me thanks!

@Artifus  that's an awesome idea, i'll be checking for your sound sample,  can you tell me what type of preamp your using with this thing ?  Normal Di for guitar level?


Thanks alot again peeps!!!

[Mac Walker]

the drill thing is a good idea, i thought about it, i'm just not sure how i would feed the wire from the spool with a reliable system without breaking
the wire (45 gauge is pretty slim and easily breakable, Pain)  Do you have pics of how you fed the wire to the drill ?? 

Check out this from Stewmac -

http://www.stewmac.com/freeinfo/Electronics/Pickup_building/a-homemadewinder.html

The trick is to orient the spool so it is not spinning itself while wire is being pulled, the wire is perpendicular to the spool (see the third picture in the link)....

[J0K3RX]

ideas ideas ideas...


Great stuff here!!
http://www.tdpri.com/forum/tele-home-depot/241964-diy-scatter-pickup-winder.html

[PRR]

> the dc resistance on one of them, roughly 46 ohm

XLR-type dynamic mikes (without internal transformer) will be 100-300 ohms.

High-impedance (guitar or DI) pickups will be, as mentioned, many K.

You need a LOT more turns.

It takes Abigail Ybarra a couple minutes on a high-speed winder to do a guitar pickup.
http://www.youtube.com/watch?v=FyPEqJRd9L8
The core looks "slow" only because the camera frame-rate "wagon wheels" against the core rotation. It's probably several thousand RPM (faster than many drills and out-of-sight from a record player).

[artifus]

can you tell me what type of preamp your using with this thing ?

i just googled 'low impedance pre amp' and found some stuff on common base amplifiers. here's some links i ripped off the schematics from referenced when designing my pre:

http://www.zen22142.zen.co.uk/Circuits/Misc/Sp-mic.htm

http://www.joebrown.org.uk/wp/?p=7225&print=1

[PRR]

Common-base is no advantage in low-noise audio. (It has different advantage in HF radio circuits.)

If he comes up above 100 ohms, a conventional "XLR" mike preamp is fine.

[artifus]

Common-base is no advantage in low-noise audio. (It has different advantage in HF radio circuits.)

If he comes up above 100 ohms, a conventional "XLR" mike preamp is fine.

it was with reference to this project: http://www.diystompboxes.com/smfforum/index.php?topic=98772.0 using pickups of 8 - 64 ohms.

[Mark Hammer]

I've been making my own pickups since the late 70's.  While a motor-based winder is fine, if one is only interested in one or two pickups a year, for experimenting with, investing the time, money and effort to set up a pickup-winding system strikes me as overkill.  If I had a business, then taking 10 minutes per pickup, instead of 30 would make a huge difference.  BUt 40 extra minutes in a year is not going to kill me.

Equally important, I don't get my wire in standard-sized spools that I can develop a tension-control system for.  Some are small and some are 6" in diameter or more, with a few pounds of wire on them.  Those ones are not going to spin on a platter.  Or at least tugging on #42 wire is not going to make them move around in circles, no matter how good the bearing are on the platter.

I have wound some pickups using a variable-speed electric drill, but I would not recommend it for anything over #40 or #41 wire.  If you have a big spool like me, there is every chance a winding will catch on the edge of the spool on its way to the pickup coil, and snap.  And unless you can feel the tension with your fingers and stop the winding instantaneously, you may find yourself having to mend more than wind.  A motor-based system is not going to be good at instantly responding to snags.

For pretty much all my pickups, I've used an old-fashioned manual hand drill, clamped to the bench or mounted in a vise.  Depending on which of my drills I use, I get between 3.25 and 3.75 turns per handle crank.  Once I get in the groove, I can crank at about 70-80RPM, which can translate into 300 turns on the coil in a minute, or 3000 in 10 minutes, or one Strat coil in about 25 minutes.  It takes longer than that because I can't crank continuously for 25 minutes straight.  But it would still take longer to drive to the music store and back to buy one, so I figure I'm ahead.  Because I can feel the snag and pullback coming in my fingertips, I stop cranking the handle immediately, and there is no momentum to pull further.  Your hand is the perfect stepping motor.

Critical to a pleasing wind is making sure you have a good precise chuck in whatever you use, and that whatever you are using to secure the coil or bobbin to the chuckis holding the coilform/bobbin as perfectly perpendicular to the axis of motion as possible.

I wind mine with the spool on the floor, below the bobbin/drill, sitting on a piece of black felt or foam.  The black background makes it easier to see the wire in the middle of the spinning coil as you are looking down at it, so you can feed the wire back and forth for a smooth even wind...or engage in "scatterwinding" if you want.  Whatever you do, you don't want the wire bunched up at the top or bottom of the coil, and seeing the wire helps to avoid that.

As well, the better the guiding, the tighter the coil, and the more winds you can fit into a smaller space.  Loose coils are microphonic, and take up more space with the outer windings ending up farther away from the polepieces/slugs, yielding less signal and certainly less top end.

If you want top make lots of pickups, using a standardized wire and spool, certainly consider a winder, but for starters a hand drill will do a bang-up job with minimal outlay and engineering.  I've made some pickups with my hand drill that will stand up to some of the best.

[Kesh]

I have wound some pickups using a variable-speed electric drill, but I would not recommend it for anything over #40 or #41 wire.  If you have a big spool like me, there is every chance a winding will catch on the edge of the spool on its way to the pickup coil, and snap.  And unless you can feel the tension with your fingers and stop the winding instantaneously, you may find yourself having to mend more than wind.  A motor-based system is not going to be good at instantly responding to snags.

For pretty much all my pickups, I've used an old-fashioned manual hand drill, clamped to the bench or mounted in a vise.  Depending on which of my drills I use, I get between 3.25 and 3.75 turns per

Not found this a problem even with #43. Distance from spool to drill is the key, at least 3 feet, and checking that the spool rim is smooth.

If I wind at 400rpm (full throttle on low speed setting) I don't get breakages. I like how knowing the rpm means I can count turns by timing the winding.