Electric guitar pickup - without permanent magnets: Core material, etc - Page 1
Forum section: electronics / projects

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 05, 2019, 02:28:13 pm
content: Howdy,so I saw this YT video (can't watch & link proper time index right now - will search this later), called something like "Uli Jon Roth rig rundown" (or gear rundown or such).Somewhere in the video, UJR speaks about his "Sky Guitar" pickups, which very much intrigued me:Instead of permanent magnets like regular electric guitar's pickups have, his uses an extra coil*, to provide the magnetic field to magnetize the steel strings whose movements then induce the current in the regular pickup coil. (he did not say it quite like that explicitly, but that's what I imagine - making a coil optimized for pickup tonal properties vs. one to magnetize a core with DC would be different requirements I guess, so I'd assume 2 stacked coils or such).The advantage of this is that he can switch more fully between single-coil pickup vs. humbucking pickup modes, in that the single coil mode will have only the magnet for one coil active, while the other one is off, and thus not additionally (mechanically) dampening the strings, like you would have with the regular "split coil switch" on some guitars with humbucking pickups, where, for single coil mode, one pickup coil is "hanging in the air", while still 2 rows of magnets are impacting the strings. And that times 2 or 3, depending on how many pickups a guitar is fitted with.I wonder now, what kind of material would be needed for the core of such a doubly tasked coil - producing a steady field by DC, and picking up audio range (60 to 8k Hz maybe) changes?And other considerations to make?Wouldn't it be nice to 3D-print the plastic parts of such a thing and make one's own custom pickup... especially with this principle - I won't quite dish out the money for the Sky Guitar just for that nice little trick* and external power supply via 1 wire of a stereo TRS cable, as a battery won't last long, he said.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 05, 2019, 03:29:13 pm
content: To pick up a magnetic field nicely the core would need to be magnetically soft. As there is a air gap there is no need for super high µ and it is very unlikely to get a high DC field. So a soft ferrite is probably the right choice for the core material.I somewhat doubt it would make a big different in damping from the open coil and permanent magnet. This usually should not give much damping as there is not much current flow in an open coil, and the frequencies should be low enough that the winding capacitance should not yet be an issue to make it electrical resonant.At small scale an electromagnet is poor efficiency. So it would mainly produce heat. So I don't think this is a good idea. Modern permanent magnets are quite powerful in comparison.

author: bob91343
author_rank: Super Contributor
timestamp: June 05, 2019, 04:25:58 pm
content: You need a magnetic field for coil motion to generate voltage. A second coil can provide that. The only caveat is that the second coil's field be strong enough to accommodate the signal amplitude to avoid distortion.Another approach could be a nonmagnetic one. Piezoelectric, for instance, or a resistance that varies with motion or pressure. A crystal microphone element for instance.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 05, 2019, 04:28:50 pm
content: Quote from: Kleinstein on June 05, 2019, 03:29:13 pmThis is aboutmechanicaldampening of the string vibrations by the magnetic fields, reducing the duration which the strings continue to vibrate (sustain). Since even adjusting pickup height (distance to strings) makes a difference, this should definitely make a difference. (I haven't measured it myself, it's common wisdom. Maybe to be taken with a grain of salt)If you have a pickup which can switch off half of its magnets when only one half of it is used for picking up the signal, it's mechanical dampening of the strings is 1/2. A guitar with 3 single coil pickups - assuming roughly the same magnetic strength and string gauge & material & distance of magnets to strings, might have 1/6 the dampening of a guitar with 3 humbucking pickups?

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 05, 2019, 04:39:27 pm
content: Quote from: bob91343 on June 05, 2019, 04:25:58 pmElectric guitarists (heh, that sounds funny) don't want their guitars to be microphonic, I would say. This invites feedback on stage. Also, you won't have the typical sounds and sound options from switching between differently positioned pickups.This really is about emulating more closely having both, a Stratocaster type guitar, and a Gibson SG or Les Paul one, in one instrument, at least sound wise. So every other aspect of this would have to be "traditional", I guess.The hint about distortion is duly noted.I guess measuring the magnets' strengths of some typical pickups would be a good idea as a start.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 05, 2019, 06:36:42 pm
content: I don't know much about electric guitars, but I know quite a bit about mechanical damping and resonance. The pickups are likely one a very small contribution to the mechanical damping. Probably just the air and also the fixtures at both ends will contribute more to the damping. According to Wikipedia damping might be a concern for high output pickups with very strong magnets. This suggests that more normal lower level ones are not an issue. An electro-magnet would be on the weak side. The there would be a minimal difference between no and a weak field.If one is concerned with damping, I would consider a different core material - so no massive metal, but more like ferrite or thin sheet amorphous.The strings can vibrate in different directions and different pick-ups may be sensitive to the different directions. Normally I would expect the distance to the pickup to dominate. In principle this can be different mode of vibration of the strings.Also just the position of the pickup along the string gives different amounts of harmonics.p.s:One could still adjust the magnetic field from permanent magnets be mechanical means, moving the magnets or part of the magnetic circuit in the back. In the reluctance type sensors any hum from the magnet would contribute to the signal. So an electromagnet would be also difficult and noise prone.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 05, 2019, 07:49:14 pm
content: Duh, wikipedia! Lol. Didn't occur to me to look there, and you found something.Well, a lot of humbuckers are considered "high output", but perhaps not the vintage ones, other than they have +6dB compared to single coil just by virtue of putting two in series.I was also wondering whether differently placed "magnetic dampeners" (placed on different positions over the string, with the center as reference), would dampen harmonics differently and producing a different "sound animation" by that, next to a changed overall envelope shape by general dampening.I can easily imagine why it is that you get more fundamental frequency, picking it up closer to the middle of the string length, and more high end closer to a resting point. But the other way around, dampening in different places, seems less obvious to me.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 05, 2019, 08:24:14 pm
content: Dampening at different positions would be essentially the same as with the pick-up intensity. The power removed is proportional to the signal level on gets out. Starting close to the fixed end, the amplitude will initially go up linearly with position for all harmonics and than peak out for the higher harmonics first. So I am afraid there is not that much option to preferably dampen or get more of the harmonics just by position. The practical position for the pick-up is likely limited to close to the resting point. It is more like on could avoid damping of some harmonics at some point (e.g. 5 fold frequency at 1/5 the length). So it's probably good to stay close the resting point to avoid getting a kind of notch effect, losing some frequency.I think in the video the active pickup is just having an amplifier close to the pickup, so that it does not have to drive the cable. This alone could reduce the loading and possible 'noise' (e.g. cable movements) pick up.If there is damping from the pickups it would be something like the power coming out of the pickup and eddy-currents in the core and magnet. So for low damping something like a ferrite core and ferrite magnet should work. Due to the air gap, the field strength should be well below the 0.3 T limit for the usual soft ferrites anyway.With the humbuckers and 2 coils there are 2 active variable air gaps. So I would expect twice the signal from each coil in addition to the +6 dB (+3 dB with loading) from having 2 coils in series.

author: 2N3055
author_rank: Super Contributor
timestamp: June 05, 2019, 09:28:33 pm
content: I agree with Kleinstein.To get same electric signal you need same magnetic change, and therefore magnetic field. That will give you same damping.Even if you could audibly change damping, what would switching between humbucker/single have to do with changing damping?I could see this as useful to control sustain on bass guitar, so you can damp it more on purpose. That would be something that might be useful.Also , on bass, I prefer humbuckers in parallel. Sounds really nice, full and clean.Using active preamp isolates pickups from complex loads, making sound more repeatable. With passive setup, changing a cable changes the sound.

author: Benta
author_rank: Super Contributor
timestamp: June 05, 2019, 10:11:01 pm
content: As an old "electric" guitarist with a lot of experience tampering with guitars, this whole discussion about "damping" is hooey.The pickups have close to zero influence on the "damping" - the guitarist expression is "sustain", meaning how long the string will continue to vibrate after being picked. This includes fundamental frequency, as well as harmonics, which are there due to the "pick" place on the string.Central points on a solid-body guitar (apply to hollow-body as well) are:- how rigid is the body- how rigid is the fretboard- how is the bridge mounted and how is it built- which saddle mount and materialThe last 0.1% goes to the pickups (regarding sustain).Now, experimenting with the pickups makes sense, but in a different way: using single-coil pickups produces a different sound from humbuckers, and varying the magnetic field from the pickups might give some new sounds and harmonics.But it won't change the sustain.

author: 2N3055
author_rank: Super Contributor
timestamp: June 05, 2019, 10:42:51 pm
content: Quote from: Benta on June 05, 2019, 10:11:01 pmOn a bass guitar that has long sustain, putting pickups with stronger magnets an bringing pickups close to string will change sustain. Not much but it will. It will have more influence on neck pickup too, because of larger amplitude of string.But in practice, you would newer bring pickups so close because strings would hit them during playing. So like you said it doesn't matter in practice.But purposely built magnetic damper could be made, another question is why would anybody want that....

author: Electro Detective
author_rank: Super Contributor
timestamp: June 06, 2019, 01:03:33 am
content: Chuck in some EMGs, crank er up, and rock outor if you need truckloads of sustain that just won't quit, the old school Fernandez Sustainer pickup system won't disappoint

author: 2N3055
author_rank: Super Contributor
timestamp: June 06, 2019, 07:43:41 am
content: Quote from: Electro Detective on June 06, 2019, 01:03:33 amYeah, on a bass guitars, active pickups are superior. Guitar players are always a bit complicated about things, so I learned not to go into discussion with them about "best pickups" or guitars or amplifiers or anything to that matter......

author: Electro Detective
author_rank: Super Contributor
timestamp: June 06, 2019, 10:27:30 am
content: Active pickups (decent linear response ones) usually don't 'lie', especially if the player can achieve the desired sustain with technique, and a controlled bond with the amplifier in close proximity.i.e. if you like the sound of the guitar unplugged, then active pickups (single coil or humbucker) should be first choice to considerOTOH, if an axe grinder is a clueless 'elusive tone' chaser, and or can't hold their chops, rolls with cheap or semi-flat 9v batteriesthen chances are good they won't 'like' active pickups, then they'll bore us with their negative 0pinionsand forever swapping out passive pickups till they hit on the tone they think they want,till that goes south after fitting a new set of strings,or guitar upgrade or new purchase,or different amp, pedals, suss PSU/batteries, crusty leadsbored impatient partner

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 06, 2019, 03:33:00 pm
content: Just a thought, but replacing permanent magnets with an equivalent static magnetic field generated by some coil would draw a significant amount of power. That may not be very practical unless you're ready to use a big battery.

author: Benta
author_rank: Super Contributor
timestamp: June 06, 2019, 07:08:33 pm
content: Quote from: SiliconWizard on June 06, 2019, 03:33:00 pmYes, of course. In the end, the guitar will either be heavy or need extra cables for power. Don't underestimate the permanent magnets in passive pickups, they're good.Concerning sustain/decay control on guitars:A good guitarist does this with the heel of his hand just above the bridge. No need for magnetics at all.

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 06, 2019, 10:07:19 pm
content: Quote from: Benta on June 06, 2019, 07:08:33 pmWhich is why Steve Vai has a built-in "e-bow" style sustainer in at least one of his JEMs, because the dude is a total noob.Anyway, some interesting input here, will have to digest all when I've got a quiet hour or two.As for "active pickup doesn't lie" - that's not really what it's about with E-guitars, though, is it.Pickup, cable, amp, speaker are all part of the electro-mechanical modelling of the resonant guitar body that the typical e-guitar lacks, to give it character. Which is why people like to experiment with different pickups and other things. I have measured a couple, they tend to have different resonant frequencies (in the system, with same assembled capacitor in the guitar, and same external cable). Especially with lots of distortion afterwards, they can sound drastically different.I understand the benefits of on-board buffers and such. It's one of the several possible routes to go. I think UJR also has controls to shift the resonance, before it's buffered - and then there's the buffer and his cable won't alter the sound by loading the whole thing.

author: Electro Detective
author_rank: Super Contributor
timestamp: June 08, 2019, 12:37:50 am
content: Folks, if you like a bit of over the top sustain, here's an electric guitar maestro showing it done the old school way:i.e. full control of the guitar and amp volumes, awesome chopswith no pretense, hype, miles of pedals wasting stage real estate, or silly shaped axe requiredHope you like itThree piece band:youtube.com/watch?v=vkUpfw4Hf3wsame tune with band and orchestra:youtube.com/watch?v=DR8JAFpiTdc

author: TinkeringSteve
author_rank: Frequent Contributor
timestamp: June 08, 2019, 10:42:27 am
content: I like Gary Moore. Especially his playing in Colosseum II.Ah, there's even a recording... but why is the singer not on that gig... ah I remember, one of the wives, or was it of the producer, found him "too flamboyant" and nagged them to let him go or somethingHe was pretty good.I don't much like the feedback for sustain trick, though. The kind of tone you could get with that seems to be limited. Seems like a gimmick for certain situations. Feel free to correct me if I'm off, I've only tried that at bedroom sound levels sitting in front of the amp with cranked pre-gain, and as the tone is, to a big extent, produced by your air coupled feedback circuit, it seems to add a certain tonal quality that's not otherwise present...Not nearly as insane a shredder as Vai, though. (who doesn't have that big of a pedal board, IIRC).Or UJR. Watch the 1977 "sails of charon" video, where he basically invented shredding, and doesn't even look at his guitar while doing so(this integrated player ignores my timestamp:forward to 01:07past the babbling)The "silly shaped axe" comment is just, eh, silly, though. If that was addressing Uli JR - watch the video in the OP. It's not just a shape, he can play notes in the upper violin range, Gary Moore could have only dreamt of.If you see the above vid - apparently a strat will do just fine for him, if he playes notes in the regular range onlyGood reminder to listen to some Gary Moore / Colosseum II again, though!

author: Electro Detective
author_rank: Super Contributor
timestamp: June 08, 2019, 11:42:35 pm
content: Shredders and speed kings have been around for a while, Ritchie Blackmore, Alvin Lee and others were hard to beat in their day,and refreshing alternatives to the Hendrix and Clapton duopolybtw Randy Bachman in the Guess Who pulled some great sustain tones in the original 'American Woman' tuneThere's a lot you can do with a decent neck pickup in a block of good resonant wood, and playing technique, without relying on subtle amp feedbackfwiw there are parts where Gary Moore doesn't need the amp to assist in note tortureQuote from: TinkeringSteve on June 08, 2019, 10:42:27 amMany good bands 'died' that way, someone 'said' something or bonked someone they shouldn't have,homophobic issues (flamboyancy)or the best way to see the exit door are silly immature questions like 'but Dude, where's our money from the last tour..?'

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 09, 2019, 12:02:54 am
content: Quote from: Benta on June 06, 2019, 07:08:33 pmHow much power is actually needed? I'm under the impression the coax can carry quite a bit of power as DC bias.