Video of pickup capacitance as it's wax potted

[antigua]

I made a video of a Strat pickup being wax potted in order to show the relationship between time, wax uptake and capacitance. This is a continuation of an experiment started here guitarnuts2.proboards.com/thread/8959/potting-rate-uptake-change-capacitance





The drop is right about 10 seconds in, so all the times can be correlated to the video time stamp -10 seconds.  I set the camera up so that you can see bubbles emerge from the pickup's coil.



0:00 127.62pF +0.00 .
0:10 126.11pF -1.51
0:20 131.09pF +4.98 .***
0:30 144.24pF +13.2 .***********
0:40 152.38pF +8.14 .*****************
0:50 157.30pF +4.92 .********************
1:00 163.73pF +6.43 .************************
1:10 170.81pF +7.08 .*****************************
1:20 172.81pF +2.00 .******************************
1:30 174.57pF +1.76 .********************************
1:40 176.74pF +2.17 .*********************************
1:50 176.87pF +0.13 .*********************************
2:00 177.76pF +0.89 .**********************************
2:10 177.84pF +0.08 .**********************************
2:20 178.11pF +0.27 .**********************************
2:30 178.78pF +0.67 .**********************************
2:40 178.87pF +0.09 .**********************************
2:50 179.14pF +0.27 .***********************************
3:00 179.21pF +0.07 .***********************************
3:10 179.89pF +0.68 .***********************************
3:20 179.90pF +0.01 .***********************************
3:30 179.91pF +0.01 .***********************************
3:40 179.92pF +0.01 .***********************************
3:50 179.94pF +0.02 .***********************************
4:00 179.96pF +0.02 .***********************************
4:10 179.97pF +0.01 .***********************************
4:20 179.98pF +0.01 .***********************************
4:30 179.99pF +0.01 .***********************************
4:40 180.01pF +0.02 .***********************************
4:50 180.01pF +0.00 .***********************************
5:00 180.02pF +0.01 .***********************************
6:00 180.03pF +0.01 .***********************************
7:00 180.02pF -0.01 .***********************************
8:00 180.00pF -0.02 .***********************************
9:00 179.97pF -0.03 .***********************************
10:0 179.95pF -0.02 .***********************************


After the pickup cools, the final capacitance is 185pF, as the wax cools and contracts the coil.

As it can be seen, the wax potting increases the overall capacitance from 127pF to 180pF, and then after cooling, 185pF, for a total increase of 58pF. Also, most of the absorption happens between submersion and two minutes, and then it's essentially flat until the pickup is allowed to cool, but nevertheless there is a steady positive uptick, so it slowly takes on slightly more wax as time passes until it peaks at six minutes.

One take away is that, it seems to me, that the coil is fully penetrated by was without the need for vacuum potting, at least with this Strat style pickup. It might be a different story with a plastic bobbin, but I doubt it.

Another is that the capacitance increases with wax potting, 58pF is similar to an added 18 to 24 inches of guitar cable length. This can drop the resonant peak by 100Hz, give or take, depending on the inductance and the overall capacitance. Not easy to hear, but not impossible, if the resonant peak is somewhat low to begin with.

Lastly, if a person were to "lightly wax pot" a pickup, they would need to pull it at about 45 seconds, if they were to do nothing else. The earlier experiment showed that if the pickup is pulled at 30 seconds, the wax will just be clumped up on the outside of the pickup, because the pickup's surface temp is still below the melting point of the wax. But there's another technique that could be used; dip the wax in the vat really quickly, and then stick the pickup in the over at 150 degree F, or maybe leave it in direct sunlight, and allow the wax and the pickup to heat up with only the volume of wax that's coated around the pickup, and the final result should be waxed coil containing less overall wax than had the pickup been submerged for two minutes or longer.

[pablogilberto]

Great work!

What temp and wax type did you use for this?

Do you think that the temp will affect the rate of wax penetration?

I did a similar experiment at was able to confirm that the change in capacitance happened at the first few minutes.
I'm surprised to see this though.
I thought that the capacitance will go up only when the wax has fully penetrated the inner coils.

Thanks for sharing your data.

[antigua]

Jul 18, 2020 22:10:13 GMT -5 pablogilberto said:

Great work!

What temp and wax type did you use for this?

Do you think that the temp will affect the rate of wax penetration?

I did a similar experiment at was able to confirm that the change in capacitance happened at the first few minutes.
I'm surprised to see this though.
I thought that the capacitance will go up only when the wax has fully penetrated the inner coils.

Thanks for sharing your data.

I should have made note of the wax temp, I think it was about 180F, as that's what I've usually seen it hold at with this same setup before. Higher heat probably does increase the rate of penetration a bit, if not because the liquefied wax is thinner, then because the copper coil will have expanded more under higher heat.  I doubt the difference is significant, because the wax is very oily and ultimately it penetrates the coil via capillary action. 

The capacitance is a good proxy to measure the ratio of air to wax, because the dielectric value of air is 1, where as the value of the wax is about 2.2, so for every unit of volume of air that is replaced by wax, the capacitance of that particular unit increases from 1 to 2.2. 

If the capacitance starts out at 125pF and ends at 175pF, then that means the capacitance increased by only 40%, but the dielectric value of the wax is 2.2 times greater than air. Therefore, if you conceptualize the coil as a plate capacitor, then only a fraction of the plates are separated by air/wax, the rest is only separated by the insulator on the wire, because if the theoretical plates have a uniform air separation, the capacitance should cleanly multiply by 2.2.  Given  ( 125pF - x ) * 2.2 = 175pF , x = 45.5pF,  45.5pF / 125pF is .364, so 36% of the lumped capacitance is subject to air/wax, while the remainder of the lumped capacitance was not affected. If the coil were wound tighter, there would presumably be a smaller ratio of air and wax, and vice versa. 

[pablogilberto]

Hi antigua

How do you know if the coil is fully penetrated?

I tried wax potting a strat pickup at 180F.

During the first 2 minutes, I can see lots of bubbles coming out.
After this, the bubbles starts to slow down.

After 25minutes, there are still micro bubbles but they are very tiny compared to the ones during the first 2 minutes.

Is this normal? Or should I wait for more time to the wax to fully penetrate?

Thanks

[antigua]

Jun 24, 2021 1:08:13 GMT -5 pablogilberto said:

Hi antigua

How do you know if the coil is fully penetrated?

I tried wax potting a strat pickup at 180F.

During the first 2 minutes, I can see lots of bubbles coming out.
After this, the bubbles starts to slow down.

After 25minutes, there are still micro bubbles but they are very tiny compared to the ones during the first 2 minutes.

Is this normal? Or should I wait for more time to the wax to fully penetrate?

Thanks

I don't know that the coil is fully penetrated in that I didn't cut it open and look, but theres not much reason to suspect that air remains trapped in the coil once the bubble cease. The final capacitance measured is as high, if not higher than most I've measured, with a capacitance around 180pF. Capillary action and the low surface tension of the heated paraffin causes the wax to easily penetrate the windings. 

A lot of pickup makers advertise "light wax potted" and it stands to reason that if you wax pot just the outer most layer of the coil, it will no longer be microphonic, or sensitive to changes in sound pressure level. So if a pickup maker were telling the truth, and they actually set out to "lightly wax pot" a pickup, because we have to trust that they're telling the truth as we can't cut the coil open and see how much was is there for ourselves, the pickup maker would want to do this.. Heat up the pickup to 130 degree or so, so that when the pickup is submerged, the wax will instantly penetrate the coil and does not solidify around the room temperature pickup, which leads to uneven penetration as the coil heats up in the wax in a non-uniform way. The pre-heated pickup would need to be in there less than 30 seconds, probably no more than 15, so that the wax does not fully penetrate the coil.

In my experiment below, the pickup was not pre-heated, and there's no penetration for the first 20 second, because of that heat differential between the wax and the room temperature pickup, and when the pickup finally did permit wax, it was uneven because some parts of the coil heated more quickly than other parts, so the penetration was not even at first, and if you want to pull the pickup out as quick as possible, you would want it to penetrate evenly. 

Pickup makers claim to use a "vacuum wax pot" pickups for through penetration, and it seems to me that no vacuum is ever necessary. But they also claim sometimes, to "lightly wax pot" pickups which is the opposite ideal. So which is better? I don't think they really know or care, it's whatever the customer thinks is the better sales pitch. Personally I like the idea of only leaving in the wax for as little time as possible, because to suppress microphonics, only outside of the pickup need be waxed. I'm also interested in lacquer dipping as a means of quieting a pickup, but I don't know much about that process. Lacquer is a lot thicker than heated wax, it probably penetrates the coil much less, too.  

[pablogilberto]

Hi antigua

I have tried wax potting via dipping just like what you did. I did 30mins at 180F

I dissasembled the pickups and checked the internals. Found out that the wax does not fully penetrate the inside (upto the polepiece.
Comparing to a Seymour Duncan that I have opened, the wax is full and solid in between the polepieces.
I think they used vacuum wax potting.

Now, I really wanted to try this myself and compare results (speed of process) vs overall increase in capacitance.

Found this video.


Do you have suggestions on how to setup a home-made system like this?
I only have the wax heater. Not sure with the other tools.

Thanks!

[antigua]

Jun 29, 2021 7:37:20 GMT -5 pablogilberto said:

Hi antigua

I have tried wax potting via dipping just like what you did. I did 30mins at 180F

I dissasembled the pickups and checked the internals. Found out that the wax does not fully penetrate the inside (upto the polepiece.
Comparing to a Seymour Duncan that I have opened, the wax is full and solid in between the polepieces.
I think they used vacuum wax potting.

Now, I really wanted to try this myself and compare results (speed of process) vs overall increase in capacitance.

Found this video.


Do you have suggestions on how to setup a home-made system like this?
I only have the wax heater. Not sure with the other tools.

Thanks!

How tightly wound the coil is might be a factor in the uptake of wax. But why would you want full wax penetration, from a practical stand point? Is the pickup in question still to microphonic? In any event, I don't know how to make a vacuum sealed potting rig, I used candle making supplies.

[pablogilberto]

Yes, the pickups are still microphonic. This is a humbucker btw.

It was originally wax potted but microphonic.
I tried wax potting using the same method I use with other pickups. I dipped it for 30minutes.
Was surprised that it is still microphonic.

That's why I wanted to try a full penetration.

Thanks

[antigua]

Jul 4, 2021 9:45:18 GMT -5 pablogilberto said:

Yes, the pickups are still microphonic. This is a humbucker btw.

It was originally wax potted but microphonic.
I tried wax potting using the same method I use with other pickups. I dipped it for 30minutes.
Was surprised that it is still microphonic.

That's why I wanted to try a full penetration.

Thanks

It might not be the coils, it could be the cover or other metal parts that are just loose enough to wiggle and cause feedback. Did you submerge the entire pickup with a cover already attached?


It's true that I haven't tried this with PAF style bobbins, though. Capacitance was my primary interest in this case, and the capacitance is always pretty low with a PAF because of the series coil arrangement. 

[gckelloch]

Another useful experiment for sure, Antigua. Generous of you to give your time for this. I’m thinking that the capacitance increase may have more to do with insulation stretching from heat than from the wax itself. Consider that there wouldn’t be much space left between the insulation of each wire after winding under tension, and the wax would only fill in the spaces beside the smallest distance between adjacent wires. The capacitance of the wax may not make any difference at all in that case, no? My guess is the capacitance lowers at first as the insulation expands while heating up, and then increases as the insulation under higher tension around the bobbin edges stretches thinner than when b4 being heated. Might be interesting to see how PE vs Poly or Formvar coils would fair?

[antigua]

Jul 15, 2021 22:33:19 GMT -5 gckelloch said:

Another useful experiment for sure, Antigua. Generous of you to give your time for this. I’m thinking that the capacitance increase may have more to do with insulation stretching from heat than from the wax itself. Consider that there wouldn’t be much space left between the insulation of each wire after winding under tension, and the wax would only fill in the spaces beside the smallest distance between adjacent wires. The capacitance of the wax may not make any difference at all in that case, no? My guess is the capacitance lowers at first as the insulation expands while heating up, and then increases as the insulation under higher tension around the bobbin edges stretches thinner than when b4 being heated. Might be interesting to see how PE vs Poly or Formvar coils would fair?

That's a good point about the initial drop of capacitance, I'd wager it is due to due the coil expanding. It could also be due to a change in the copper's resistance, but I don't think the small variation in resistance would throw the capacitance measurement off. Measuring the capacitance with respect to heat alone, and not the wax, could make the effects of heat alone more clear. That's especially academic since guitars are generally kept at room temperature. 

I think the dielectric value of the wax is in play, mostly because if you do the same experiment with water, you see the capacitance rise even higher, towards 250pF, and the dielectric value of water is higher than wax. The insulation meanwhile seems to be pretty stable at these lower temperatures, I think it can be burned off with a soldering iron, but that's over 500 degrees f. After cooling, the capacitance increased another 5pF, which is probably due to the coil contracting, so maybe it can be deduced that the capacitance had dropped about 5pF due to heat expansion. 

[gckelloch]

Jul 15, 2021 23:19:07 GMT -5 antigua said:

Jul 15, 2021 22:33:19 GMT -5 gckelloch said:

Another useful experiment for sure, Antigua. Generous of you to give your time for this. I’m thinking that the capacitance increase may have more to do with insulation stretching from heat than from the wax itself. Consider that there wouldn’t be much space left between the insulation of each wire after winding under tension, and the wax would only fill in the spaces beside the smallest distance between adjacent wires. The capacitance of the wax may not make any difference at all in that case, no? My guess is the capacitance lowers at first as the insulation expands while heating up, and then increases as the insulation under higher tension around the bobbin edges stretches thinner than when b4 being heated. Might be interesting to see how PE vs Poly or Formvar coils would fair?

That's a good point about the initial drop of capacitance, I'd wager it is due to due the coil expanding. It could also be due to a change in the copper's resistance, but I don't think the small variation in resistance would throw the capacitance measurement off. Measuring the capacitance with respect to heat alone, and not the wax, could make the effects of heat alone more clear. That's especially academic since guitars are generally kept at room temperature. 

I think the dielectric value of the wax is in play, mostly because if you do the same experiment with water, you see the capacitance rise even higher, towards 250pF, and the dielectric value of water is higher than wax. The insulation meanwhile seems to be pretty stable at these lower temperatures, I think it can be burned off with a soldering iron, but that's over 500 degrees f. After cooling, the capacitance increased another 5pF, which is probably due to the coil contracting, so maybe it can be deduced that the capacitance had dropped about 5pF due to heat expansion. 

Perhaps it could be that water, being more viscous, simply goes deeper into the coil and softens more of the insulation around the bobbin edges? Perhaps the result is a combination of both factors?

[antigua]

Jul 16, 2021 2:21:06 GMT -5 gckelloch said:

Perhaps it could be that water, being more viscous, simply goes deeper into the coil and softens more of the insulation around the bobbin edges? Perhaps the result is a combination of both factors?

Once the water evaporates, the capacitance reduces again.

[gckelloch]

Jul 16, 2021 15:45:45 GMT -5 antigua said:

Jul 16, 2021 2:21:06 GMT -5 gckelloch said:

Perhaps it could be that water, being more viscous, simply goes deeper into the coil and softens more of the insulation around the bobbin edges? Perhaps the result is a combination of both factors?

Once the water evaporates, the capacitance reduces again.

To the value it was b4 heating?

[antigua]

Jul 18, 2021 1:37:46 GMT -5 gckelloch said:

Jul 16, 2021 15:45:45 GMT -5 antigua said:

Once the water evaporates, the capacitance reduces again.

To the value it was b4 heating?

It appeared so, yes, but it was a wax potted pickup that was then boiled in water, not a wholly unpotted pickup. It started somewhere around 160pF, got up to 230pF but eventually returned to around 160pF. The water displaced some of the wax, and then evaporated off after some time.  Here's the thread guitarnuts2.proboards.com/thread/8739/wax-potting-experiment-capacitance-microphonics   The goal of the test was to see how much wax I could draw out of the coil, so the testing was focused around that, the water observations were secondary. I tried various solvents as well, but nothing I tried was able to remove all of the wax. 

I don't see much evidence of the coil's insulation being permanently deformed by the heat. The temp rating of the Remington "Heavy Formvar Copper Wire" is 220F, and 300F for "Enameled Copper Wire". I don't recall which was used in the test pickup. The highest heat I used was 205F. I never noticed any strange smells, or the pickup's wire fusing, which I suspect would occur if the insulation reached a melting point.