|
|
Post by ozboomer on Sept 11, 2020 6:58:55 GMT -5
At the risk of starting a 'Forum Fury™️', let me pose the following... I've been thinking 'electronics' again lately (maybe a bit too much, huh?  ) ...and I'm trying to understand the 'problem' of a 'microphonic' pickup. In a dynamic microphone (which is as close as I can visualize for this), we have a coil around a magnet... but the coil is attached to a diaphragm. So, as sound makes the diaphragm vibrate, this makes the coil move with respect to the magnet, inducing a current in the coil. IN a guitar pickup, though, this movement would need to be (relatively) 'large' to get a sizable current induced in the coil wire... particularly compared to the current induced by the steel string moving through the magnet's field. In the pickup, the coil doesn't move at all with respect to the magnet. So, how do we get a pickup being 'microphonic'? Even if you say the body vibrating does something, the coil and the magnet would move together, hence no current (Memories: 'It's not the change in flux.. but the rate of change of magnetic flux...') Similarly, if a pickup has a metallic cover, again, the cover is 'attached' to the pickup (somehow) so the cover also vibrates (in the vibrating body OR the pickguard OR from a resonance with some other frequency source)... but the cover can't move with respect to the coil and magnet, hence no current. I've only seen discussions around wax-potting pickups (which suggests restricting the movement of the coil wire)... but again, the coil wire is wound onto the bobbin and can't move with respect to the magnet... can it? (as he starts to doubt his original idea)...I can understand how the 'ugly' sounds heard may be something to do with feedback... but that's a 'physical' frequency resonance thing, with output from the amplifier 'forcing' the strings to vibrate 'in sympathy' with the amplifier output... and is not an 'electrical' thing related to the pickup, per se -- it's more about how the strings vibrating react to the volume of the amplifier output... It still boils down to the movement of coil wire with respect to the magnet for any reason, is going to be small (inaudible in either volume or frequency?) when compared to what the vibrating strings are doing... isn't ti? I'd appreciate folks pointing out the fallacies in my thinking... so I can get some sleep again |
|
|
|
Post by b4nj0 on Sept 11, 2020 13:15:39 GMT -5
Coil(s)/magnet(s)/reciprocity.
A loudspeaker can be persuaded to deliver an amplifiable output if you scream into it. A pickup will transduce the audio from a loudspeaker if you bring the two close enough together. It boils down to the degree of mutual coupling in each case. A good pickup should minimise microphony but it's always going to be there to some degree just the same.
I'm sure that others on here could be more eloquent than that?
e&oe ...
|
|
|
|
Post by reTrEaD on Sept 11, 2020 15:27:03 GMT -5
In the pickup, the coil doesn't move at all with respect to the magnet. So, how do we get a pickup being 'microphonic'? A pickup is microphonic when the first statement is not true. Your coffee cup (and the coffee within) won't move with respect to your car's center console if the cup is glued to the console and the coffee is frozen solid. (That's much the same approach employed when potting a pickup.) BUT ... if the coffee is not frozen and the cup isn't glued ... beware of bumps in the road! |
|
|
|
Post by ozboomer on Sept 11, 2020 20:37:09 GMT -5
Okie... So then, the issue is that the coil (wire) is assumed to move with respect to the magnet...
..but isn't the 'scale' (amplitude of signal) the issue here then? An E string (0.23mm/0.009") vibrating with a total displacement, say, of ~5mm/0.2" at most over a length of ~650mm/25.5" would generate a current of "X". Isn't a 'segment' of (42AWG/0.06mm/0.0025") coil wire that's ~66mm/2.6" long (the turns of the coil can't move) vibrating with a displacement of 0.5mm/0.02" ([erroneously] assuming a linear scaling... and that the wire can even move, given the tension it has applied to it over a relatively short distance) only going to generate a current of "significantly less than X"? (I've forgotten most of my electrical engineering maths) ...and its effects on the sound, therefore, will be inaudible?
Anyway, given the technology options we have these days, why hasn't anyone built an opto-isolated pickup based on LEDs (much how MIDI circuits work)?
|
|
|
|
Post by ashcatlt on Sept 11, 2020 21:39:00 GMT -5
..but isn't the 'scale' (amplitude of signal) the issue here then? Well, yes but also proximity. Basically the coil wire is just right there about as close to the magnet as you can get, and its movement directly induces current in itself. The string is trying to drag the magnetic field around from relatively far away. But also, with enough gain/distortion, it doesn't really take all that much to squeal really loud. I've done things where my guitar was feeding back like crazy (really string feedback, but the point I think is the same), but listening to the recorded DI, it's a heck of a lot quieter than any of the actual picked stuff. |
|
|
|
Post by ozboomer on Sept 11, 2020 23:52:23 GMT -5
Ok.. I think I'm getting a bit of a handle on this then... With all my experimenting and such over the years (and fiddling about with maybe 60 or 70 pickups), I've never really run any of my gear with mega-high gain... and/or any major distortion/overdrive... and when I DO run things a bit 'hotter', the guitar output is going directly into a computer interface or a headphone amp, so the sound never hits the 'same air' as the pickup... hence, I don't experience the phenomenon. So, more than anything else, if you DO run your setup with 'high gain', you *might* find your pickups are 'microphonic'... but it's (frequently) nothing more than dumb luck, rather than a design issue; that the particular pickup is 'built' (and is installed in a particular guitar, used with particular strings and run through a particular amp with certain characteristics) such that it will be 'microphonic'; akin to the favourite of civil engineers everywhere, the 'perfect storm' of span, material, loading and weather conditions, viz:- So, I guess this is why folks (and some pickup manufacturers) will 'wax-pot' pickups. Perhaps you could also use Silicone sealant... or even Blu-Tack to 'immobilize' the coil wire... ...but I wonder if people who have experienced the problems have tried to change the other variables instead of just looking at the pickups? Obvious things, like changing the volume at the guitar and amp.. and physically getting the guitar out of the 'line of projection' from the amp speaker will do a lot... but how about using a CRO (or software equivalent) to isolate the 'resonant' frequency and use some EQ to notch it out? After all, isn't it the same (or at least a similar) problem to dealing with the 60/50 Hz "hum"? Always keen to explore ways to get around 'problems of our own making'... 'coz I have 'an inquirin' mind' (sometimes).. |
|
|
|
Post by ashcatlt on Sept 12, 2020 11:56:01 GMT -5
Well, my Teisco (or whatever, the actual brand isn’t legible, but definitely in that family, it’s the one in my profile pic) bass is so microphonic that you can hear my fingers on the pick guard without too terrible much gain and even after my attempt to pot it in wax. My Xavier 335 copy isn’t much better. Some guitars you can actually sing through the pickups. It’s not always just the squealing that gets annoying.
|
|
|
|
Post by frets on Sept 12, 2020 15:56:38 GMT -5
How ‘bout the quick dunk into thinned lacquer. Anybody tried that?
|
|
|
|
Post by thetragichero on Oct 1, 2020 15:14:58 GMT -5
yes lacquer is another option that is/can be used. i like wax because i can do it myself (i have a mini crockpot whose lid broke that i give my coffee can full-o-wax a hot bath in) and since i use a paraffin/beeswax mixture makes the house smell lovely (now, i happen to enjoy the smell of paint maybe a little too much but the same cannot be said of my better half)
|
|
|
|
Post by rogerioprazeres on Oct 1, 2020 16:39:23 GMT -5
|
|
|
|
Post by antigua on Oct 12, 2020 12:44:43 GMT -5
At the risk of starting a 'Forum Fury™️', let me pose the following... I've been thinking 'electronics' again lately (maybe a bit too much, huh? ) ...and I'm trying to understand the 'problem' of a 'microphonic' pickup. In a dynamic microphone (which is as close as I can visualize for this), we have a coil around a magnet... but the coil is attached to a diaphragm. So, as sound makes the diaphragm vibrate, this makes the coil move with respect to the magnet, inducing a current in the coil. IN a guitar pickup, though, this movement would need to be (relatively) 'large' to get a sizable current induced in the coil wire... particularly compared to the current induced by the steel string moving through the magnet's field. In the pickup, the coil doesn't move at all with respect to the magnet. So, how do we get a pickup being 'microphonic'? Even if you say the body vibrating does something, the coil and the magnet would move together, hence no current (Memories: 'It's not the change in flux.. but the rate of change of magnetic flux...') Similarly, if a pickup has a metallic cover, again, the cover is 'attached' to the pickup (somehow) so the cover also vibrates (in the vibrating body OR the pickguard OR from a resonance with some other frequency source)... but the cover can't move with respect to the coil and magnet, hence no current. I've only seen discussions around wax-potting pickups (which suggests restricting the movement of the coil wire)... but again, the coil wire is wound onto the bobbin and can't move with respect to the magnet... can it? (as he starts to doubt his original idea)...I can understand how the 'ugly' sounds heard may be something to do with feedback... but that's a 'physical' frequency resonance thing, with output from the amplifier 'forcing' the strings to vibrate 'in sympathy' with the amplifier output... and is not an 'electrical' thing related to the pickup, per se -- it's more about how the strings vibrating react to the volume of the amplifier output... It still boils down to the movement of coil wire with respect to the magnet for any reason, is going to be small (inaudible in either volume or frequency?) when compared to what the vibrating strings are doing... isn't ti? I'd appreciate folks pointing out the fallacies in my thinking... so I can get some sleep again What you're missing is the capacitive potential, so instead of a dynamic microphone, think of a condenser microphone. All of the parts of the pickup that are grounded have a capacitance with respect to the hot parts (much of the coil, the hookup wire), and when vibrations hit the pickup, that capacitance value changes slightly, and you get a voltage as a result of that sudden change in capacitance. It becomes reciprocal and feedback ensues. |
|
|
|
Post by blademaster2 on Oct 12, 2020 14:42:03 GMT -5
That would only hold true if a condenser microphone worked without phantom power. With no phantom power to offer a DC bias the change in capacitance cannot (should not be able to) generate a signal. My understanding is that "microphonic pickups" do indeed work the same way that a dynamic microphone does - any ability for the coil wires to move even a little within the magnetic field of the pickup will generate a signal. The resonance of these small, short spans of wire within the windings creates a fairly high shriek sound to most ears. That is why wax potting (or epoxy/araldite potting) reduces this effect by hold them more-or-less motionless relative to the magnet. |
|
|
|
Post by antigua on Oct 12, 2020 15:46:16 GMT -5
That would only hold true if a condenser microphone worked without phantom power. With no phantom power to offer a DC bias the change in capacitance cannot (should not be able to) generate a signal. My understanding is that "microphonic pickups" do indeed work the same way that a dynamic microphone does - any ability for the coil wires to move even a little within the magnetic field of the pickup will generate a signal. The resonance of these small, short spans of wire within the windings creates a fairly high shriek sound to most ears. That is why wax potting (or epoxy/araldite potting) reduces this effect by hold them more-or-less motionless relative to the magnet. I'm not real familiar with condensor mics, but I think the DC bias is just to ensure there is a strong voltage across the plates, so that a usable AC voltage is produced. In a pickup, there's a potential across the parts of the pickup that is very small, but then again that's why they tend to only be microphonic at high volume at gain. It's not just wire that makes a pickup microphonic, it's also loose covers, covers which are not magnetic, thus only have a capacitive potential and not an inductive one. |
|
|
|
Post by ziggystardust723 on Jan 26, 2021 0:18:49 GMT -5
Hello guys,
If you wind correctly your pickup, it don't need to be Potted:
- I got my winder Schatten 8y ago,
& at same time got a blok of Parrafine,
> but I Never used this one,
cause I pull the wire Enough:
= 0ne time, I had to wind an other one, cause the Fiber thing over was really too turned, on a Strato style pu..
- & no broken the wire..
(my bread of Parrafine is always new)
> The Sound of a pickup Not waxpotted is Unbelievable Better than a Potted:
> I saw on E-Bay, 2y ago (?.):
= a '58 Gibson Paf in selling for 3.000 $ (0nly 1, not the Set..)
> but if people did't know:
- these pickups were made on Automatic Winding machines:
called 'Leesona 102'(sold to S.Duncan & Thrôbak etc..),
- & wich were Customised machines, not 1st to wind pickups..
- But why did these pickups were really better.?
> 0nly because they were not Potted:
= the 1st Bobbins in 1957 (& before, from '55..) were not made of Plastic, but in Butyrate, & these ones did't like so much to be proof in hot Pareafine or Wax:
= they 'disapeared'..
> So, the Sound of theses pickups was really better: look at this price..
(in Paf, in 1st: the wire was wounded around Butyrate, so After around Plastic, & 0n the 'Screws Bobbin': the Screws were & Are far-away of magnet field: not at all the Same like in a 7ender Coil like a Strato or Tele etc: where the Wire is directly Wound on the Rod-Magnets..)
-I don't understand really the 1st question, cause in 8y: I never meet this kind of problem..
> When you pull enough your wire, your pickup will have no problem at all, Without be Potted:
> to Sounds well..
- Bye, Ziggy (France).
|
|
|
|
Post by ashcatlt on Jan 26, 2021 12:11:49 GMT -5
It's not just wire that makes a pickup microphonic, it's also loose covers, covers which are not magnetic, thus only have a capacitive potential and not an inductive one. IDK about this capacitive thing (I know how condensers and similar transducers work, just not sure how much it applies in this case), but I do know that if the whole pickup itself can move, you can end up with similar issues. I had one rather memorable evening playing an acoustic guitar with a sound hole pickup. I could mute the strings, but it would still feed back because the top of the instrument would vibrate, taking the pickup with it, which for all practical purpose is the same as the strings moving while the pickup stays still. Had that same issue with an electrified banjo a while later. At high enough volumes you can actually see the body of the instrument wiggling, and you can definitely feel it. It’s almost scary, but also kinda cool. |
|
|
|
Post by blademaster2 on Jan 26, 2021 13:19:01 GMT -5
I can certainly see that there is higher capacitance for paraffin potting compared to air (if the gaps are there at all and are filled with the paraffin).
Paraffin will double or even triple/quadruple the capacitance value of the interwinding capacitance in the coil compared to the same coil with air. That would have to affect the frequency response of the pickup. Tighter winding would reduce this impact, since there is no air gap (or less of an air gap) to be filled with the paraffin.
|
|
|
|
Post by antigua on Jan 31, 2021 23:22:41 GMT -5
It's not just wire that makes a pickup microphonic, it's also loose covers, covers which are not magnetic, thus only have a capacitive potential and not an inductive one. IDK about this capacitive thing (I know how condensers and similar transducers work, just not sure how much it applies in this case), but I do know that if the whole pickup itself can move, you can end up with similar issues. I had one rather memorable evening playing an acoustic guitar with a sound hole pickup. I could mute the strings, but it would still feed back because the top of the instrument would vibrate, taking the pickup with it, which for all practical purpose is the same as the strings moving while the pickup stays still. Had that same issue with an electrified banjo a while later. At high enough volumes you can actually see the body of the instrument wiggling, and you can definitely feel it. It’s almost scary, but also kinda cool. I once installed some covers on humbuckers, but I thought I could get away with forgoing the wax potting and just use double sided sticky tape. I was very wrong, they squealed a lot, and holding the strings did nothing to stop it. The pickup itself was wax potted, but the cover was just stuck over the pickup, not wax potted. There's no other explanation for that feedback outside of variable electrostatic coupling, since the cover wasn't magnetic, and the pickup had not squealing issues without the covers. The squealing only happened with a lot of gain, so the capacitive coupling could be very small, but the high gain factor makes for a big effect of an otherwise small cause. |
|
) ...and I'm trying to understand the 'problem' of a 'microphonic' pickup.
