Minimum number of turns needed for an active pickup?

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I calculated that my single piece of wire has a resistance of 0.0003627 ohms, that's pretty close to your calculations Gnobuddy.

I tried to measure it, but i didn't have any spare/broken speakers to test it. I used a monitor headphone to draw up a frequency response. It showed a flat frequency response between 100-5khz, and a gradual high roll of from that (that may have been because of the headphone/ distance from the headphone), but no resonant peak what so ever.

As for the tone change with the smaller wire, I didn't really look into that, the output was way too low.

Now i can't say that the hum sensitivity is unchanged. It's pickups way less hum than a single coil, but only if it's connected to a low impedance input. When connected to a high Z input it's noise as hell, picks up all kind of junk.

My knowledge of AC electronics with transformers is limited. I only have a theory that this is because by loading the pickup helps, because all the junk is picked up in the transformers secondary (one with many turns) and generate very little current, but relatively high voltage, by loading the secondary, most of this noise is shunted down to ground, while the guitar signal's level remains relatively unaffected because of the ultra low resistance of the primary, that can supply higher amounts of current.


I read about other experiments that use two transformers, and by tuning a dummy load ( a potentiometer ) on a secondary coil tone shaping could be achieved and resonant peaks can be added.
This is because the load on the secondary is reflected back on the primary.

My goal is actually to create an as transparent sounding pickups as possible, So i don't mind sounding too Hi-fi.


A note one Alumitone:
The coil itself is the aluminium assembly, at one a metal rod (or more like laminated sheets, presumably 0 shaped) is stick between the aluminium assembly, and the transformer is would up the metal rod itself. Their 'single coils' are also humbuckers, they have two magnets with opposing polarities,they have two secondary coils, on each side of the transformer core, to have coil splitting ability. As far as i can tell all the pickups are a single piece of aluminium, with slots on both sides, so in essence, the middle part of the two 'coils' is shared, it's essentially two coils in series, inherently humbucking design. My idea is that the secondary coils not really for 'coil taps' in the traditional sense, but more like for tone shaping.
 
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The prime parameters all scale correctly.
Exactly. You could transform the 1-turn pickup and 1:1000 transformer into an equivalent 1000 turns pickup. Loading caps for the resonant peak are placed on the hi-impedance side of the transformer.
Hum pickup that is induced magnetically should be the same in both configurations.
Hum pickup that is induced via stray capacitance may be another cup of tea.
 
My goal is actually to create an as transparent sounding pickups as possible, So i don't mind sounding too Hi-fi.
A while ago, I stumbled across a web page that you might find interesting: Guitar Pluck

The analysis on that page is of an acoustic guitar, which generates a wider range of (high) frequencies than an electric guitar. Looking at the spectrum of this particular note, there seems to be very little energy above 4 kHz. (And that's already the 13th harmonic of the 300 Hz fundamental!)

I haven't taken any FFTs, but I've been experimenting with playing both electro-acoustic and electric guitars through a flat-response speaker, with appropriate conditioning electronics in between, including a graphic EQ. If I bring up the 6.3 kHz band, the sounds I hear are ugly and scratchy, and become extremely unpleasant when the guitar is turned up to jam-night SPL (which isn't very loud, but louder than I play at home.)

For amplified acoustic guitar, and even more so for electric guitar, I would say that, to my ears, what little signal lies above 5 kHz doesn't seem to sound good. The guitar sounds better, sweeter, more musical, if I low-pass filter and remove it.

If you use a microphone in front of the acoustic guitar, the wooden body of the guitar itself does the high-passing for you. It's not easy to make a chunk of wood vibrate at 6000 Hz, so the guitar body filters out those unpleasant-sounding high frequencies by not amplifying them as well as it does the lower frequency components.

-Gnobuddy
 
My goal is actually to create an as transparent sounding pickups as possible, So i don't mind sounding too Hi-fi.

A note one Alumitone:
The coil itself is the aluminium assembly, at one a metal rod (or more like laminated sheets, presumably 0 shaped) is stick between the aluminium assembly, and the transformer is would up the metal rod itself. Their 'single coils' are also humbuckers, they have two magnets with opposing polarities,they have two secondary coils, on each side of the transformer core, to have coil splitting ability. As far as i can tell all the pickups are a single piece of aluminium, with slots on both sides, so in essence, the middle part of the two 'coils' is shared, it's essentially two coils in series, inherently humbucking design. My idea is that the secondary coils not really for 'coil taps' in the traditional sense, but more like for tone shaping.
I fitted an Alumitone to one guitar and it cleaned up the sound - very hi-fi. However after a while that became boring. Re-designing the guitar amp eq brought more satisfaction because I could temper the bad parts of pickups that had character.
 
...very hi-fi. However after a while that became boring.
I agree with you that having versatile EQ options is a fantastic tool to have in your tool box. These days, a cheap Danelectro 7-band graphic EQ pedal is always on my pedalboard. It is my most versatile and useful pedal. Starting with the EQ set flat, I find I can virtually always improve my guitar sound by dialing in some EQ, no matter what guitar or amp or type of music I'm trying to play.

I have a feeling that those of us who started with our primary interest in the world of Hi-Fi or pro audio, and who later start to play guitar, often start out with the automatic expectation that we should be using the Hi-Fi approach for guitar sound. After all, Hi-Fi is a collection of engineering requirements that makes audio reproduction sound good, so of course it should also apply to guitar, no?

IMO the Hi-Fi approach to guitar works quite well for gently strumming clean chords with your fingertips, maybe also for light picking at low volume with 100% clean tone.

Then, if we stay with guitar long enough to become reasonably versatile players, we may start to find out that the Hi-Fi approach doesn't sound particularly good even for clean guitar, and pretty much always sounds really bad for (distorted) rock guitar.

I certainly travelled down this road, and it took me quite a while - many years, actually - to realize that, when it comes to guitar sound, less bandwidth often sounds better.

This even applies to bass response, where a guitar that's been high-passed at 300 Hz often sounds better in a mix than one with flat reproduction down to 80 Hz. The low notes from the guitar don't clash with the bass and kick-drum, and everything sounds better, clearer, less muddy, less boomy.

At the treble end, the effect can be even more dramatic. Very often I hear a guitarist at a live performance whose sound has too much treble, and is so harsh that it is actually unpleasant to listen to. Then you listen to a well recorded guitar track mixed and engineered by a good engineer, and all that painful high-frequency hash has been filtered out of the sound, and what's left sounds much better for it.

I'm all for the low-noise aspect of Hi-Fi. That would be nice to have in our guitars. But I don't want Hi-Fi frequency response at all.

-Gnobuddy
 
I finally get to the point when i actually build and installed a version of the 1 turn pickup in a guitar.

For this version I used a 1:1000 current sense transformer. After that i plugged it in a preamp, it's a pretty simple non inverting opamp, for low noise i used an NE5534, With 33db gain, it has a pretty similar output level to a high gain humbucker, maybe a bit higher.

It's VERY hi-fi, if i didn't know any better i'd say that it's a piezo pickup. At a bit louder volume with distorting the feedback is not negligible. I feel that if i'd want to use it for a distorted guitar tone, i'd need to add a resonant lowpass filter in the preamp.

The noise is VERY low, especially compared to a humbucker being un-shielded like this, it's dead quite. A properly shielded guitar with a humbucker has only ~18db advantage in terms of the noise floor.


Anyway, here's a sound sample of it:
Pickup demo - 1 Turn 10mm2 copper by nemuikuma | Free Listening on SoundCloud
Sorry for the sloppy playing and it being a bit out of tune.
I feel i should add that i don't regularly use this guitar, so the string are quite old, and a bit dead sounding compared to new string.
 
...if i didn't know any better i'd say that it's a piezo pickup.
It is certainly very bright and wide-band, like some piezo pickups. But there is inherent severe harmonic distortion in all magnetic pickups using this general design (strings spaced away from pole pieces). This particular type of harmonic distortion doesn't occur with piezo pickups.


The problem is that the magnetic field near the pickup pole-pieces falls away with distance in an extremely non-linear way. The guitar string moving through this nonlinear magnetic field induces a heavily distorted waveform into the pickup coil. This distortion does not depend on the number of turns in the coil, only on the geometry of the magnetic field itself.


-Gnobuddy
 
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