Pure paraffin wax potting, and de-potting the pickup

[antigua]

This is a new thread expanding on the experiment in this thread guitarnuts2.proboards.com/thread/8739/wax-potting-experiment-capacitance-microphonics , but this time instead of using beeswax, I've used paraffin wax, which has a lower melting point and seems to be less viscous liquid and a softer solid, than beeswax. I checked the values after potting, and then used heated denatured alcohol to extract the paraffin from the coil, and checked its values again.

As in the other thread, the test pickup is a Strat type pickups that I had wound to 8,000 turns with 42AWG wire. The paraffin was heated to about 180 degree Fahrenheit. 

Summary: paraffin performs similar to beeswax when reducing microphonics and inducing capacitance. Submerging the paraffin potted pickup in heated denatured alcohol for about a half hour removed about half of the wax and caused the pickup to become microphonic again. 



Regarding capacitance, the unpotted pickup started with a capacitance of 142pF. After potting, it got as high as 220pF, but for whatever reason it ended up closer to 200pF all said and done. As would be expected, while the pickup is still cold, the wax mostly condenses around the outside of the pickup, and during that time the capacitance is unchanged, but once the pickup reaches the temperature at which the wax melts, the wax permeates the coil, releasing air bubbles. At this point, the capacitance increases, taking about one to two minutes to reach the peak capacitance, although for this test I repeatedly took the pickup out of the wax in order to measure it, causing it to cool. If left in the wax, I suspect the wax would permeate the entire coil in under a minute. For the last 10 minutes of a total of 30 minutes wax submersion, I increased the temperature of the wax from 180 to 205 degrees, but the capacitance didn't continue to increase during that time, so it seems that 180 degrees was sufficient to fully permeate the coil. The increase of capacitance was about the same with the paraffin and beeswax; about 50pF added. 

Regarding the microphonics, The way I test this is by striking the pickup with a wooden spoon about a hundred times in order to capture peak voltage outputs on a voltage-by-frequency plot with the PCSU200. I forgot to get a baseline measurement for this pickup, but I have some from other pickups that are constructed the same way. Wax potting the pickup with paraffin appeared to mean it ever bit as anti-microphonic as compared to beeswax. After removing half of the wax with heated alcohol , the coil appeared to be as microphonic as an unpotted pickup. I think it stands to reason that the outer windings, where the wax can be most easily drawn away later, are the most responsible for microphonics, because they're under less compression than the inner windings. 

Regarding weight, I bought a high precision scale, and weighed the pickup while wax potting. The initial weight of the pickup was 52.6 grams. Once fully potted, it settled at a weight of 54.2 grams, meaning the pickup carried, inside and outside, 1.6 grams of paraffin. I baked the pickups in the oven for an hour at 210 degree F, at which point the capacitance was unchanged, meaning the coil still retained all the wax, but all the wax outside of the coil melted away, and the weight was 53.4 grams, meaning that 0.8 grams had been outside of the coil, and 0.8 grams remained inside the coil. I boiled the pickup in alcohol for about 30 minutes, and this process removed some of the wax in the coil, and the final weight after this was 52.85 grams.

Regarding inductance, as the previous test showed, and as would be expected, the wax didn't change the inductance at all. But, apparently being filled with alcohol caused the inductance to drop to 1.7 henries, according to the DE-5000 LCR meter at 100Hz in series mode. Allowing the alcohol to evaporate for 30 minutes, the reported inductance increased to 1.9 henries, and after a day of drying, the inductance returned to 2.4 henries, giving me cause to believe the alcohol fully evaporated. I'm not sure why the alcohol caused the inductance to drop, it can't be due to heat alone, as baking the pickup in the oven to higher temps had virtually no effect on the inductance. 

Attempting to remove the paraffin from the coil..  the first thing I did was bake the pickup in the oven at 210 F for about an hour, and aside from all traces of wax disappearing from the outside of the pickup, the electrical measurements suggested that all of the wax remained in the coil. Then, I heated alcohol with a double boiler to about 180 degrees, it was boiling, and submerged the pickup in there for about 30 minutes. As mentioned, the inductance decreased to 1.7 henries, and the capacitance jumped to 592pF while the coil contained alcohol. As the alcohol evaporated, the inductance returned to what it was, and the capacitance dropped to 174.25, only about half way towards the original 142pF of the unpotted coil, from 200pF. So it seems that the 30 minute heated alcohol submersion managed to remove about half the wax.  

As mentioned above, the initial weight of the pickup was 52.6 grams. After being fully wax potted and then having the exterior wax melted away, it weighed 53.4 grams, and after the alcohol submersion and evaporation weighed 52.9 grams, also suggesting that about half the wax was removed. As the microphonic testing shows, the outer portion of coil appears to have more space within the windings than the inner portion of the coil, so it's probably more difficult for heated alcohol to draw the wax from those inner windings. 

While capacitance was cut by half, the microphonics seems to be substantially restored, most likely because the it's the outer-most winding that are responsible for microphonics, and it's the outer most windings from which wax was able to escape in the heated alcohol. 

In conclusion, it seems that much of the paraffin can be removed with heated alcohol. It might be the case that there are better solvents for the job, and it might be possible that hot soapy water works as well, but I tried alcohol because it's suggested for cleaning up wax removal, and is often used for herbal extraction, but I'm not a chemist, so this was a shot in the dark. Next I will try this on some production guitar pickups to see if "de-potting" is something that can be done to a pickup that has already been manufactured. 



Paraffin Wax Dipping & Removal 

No wax:

L: 2.449H
C: 142.14pF
R: 6.076 k ohms
W: 52.573 grams

1 second:

L: 2.444H
C: 142.24pF
R: 6.368 k ohms
W: 54.373g

10 seconds:

L: 2.451H
C: 141.22pF
R: 6.571 k ohms
W: 56.558 grams

30 seconds:

L: 2.450H
C: 141.29pF
R: 6.537 k ohms
W: 57.621 grams

1 minute:

L: 2.440H
C: 142.22pF
R: 6.650 k ohms
W: 57.177 grams
Note: bubbles seen coming from the flatwork holes

1.5 minute:

L: 2.443H
C: 143.21pF
R: 6.742 k ohms
W: 55.793 grams

2 minute:

L: 2.444H
C: 152.71pF
R: 6.756 k ohms
W: 54.704 grams
Note: bubbles from the flatwork and coil, wax appears to penetrate the coil now

2.5 minute:

L: 2.444H
C: 181.36pF
R: 6.828
W: 54.075 grams
Note: steady bubbles

3 minute:

L: 2.446H
C: 206.0pF
R: 6.880 k ohms
W: 54.728 grams
Note: steady bubbles, no visible wax

3.5 minute:

L: 2.450H
C: 220.0pF
R: 6.304 k ohms
W: 54.847 grams
Note: few bubbles

4 minute:

L: 2.447H
C: 213.1pF
R: 6.592 k ohms
W: 55.092 grams
Note: few bubbles, more cooling time between dips


4.5 minute:

L: 2.433H
C: 213.8pF
R: 6.695 k ohms
W: 54.826 grams

5 minute:

L: 2.445H
C: 212.3pF
R: 6.730 k ohms
W: 54.830 grams

6 minute:

L: 2.442H
C: 212.0pF
R: 6.841 k ohms
W: 54.574 grams

10 minute:

L: 2.446H
C: 205.6pF
R: 6.990 k ohms
W: 54.371 grams

20 minute:

L: 2.440H
C: 202.0pF
R: 7.048 k ohms
W: 54.255 grams

30 minutes, final 10 mins from 180 to 205 degrees F

L: 2.439H
C: 199.16pF
R: 7.247 k ohms
W: 54.159 grams

1 hour in an oven at 210 degrees F

L: 2.451H
C: 202.5pF
R: 6.628 k ohms
W: 53.359 grams
Note: pickup looks very clean, nox visible wax on the outside of the pickup

Submerging potted pickup in alcohol at 150F for 30 mins, immediately after

L: 1.682H
C: 592.1pF
R: 6.328 k ohms
W: 54.031 grams

Submerging potted pickup in alcohol at 150F for 30 mins, 1 hour later

L: 1.914H
C: 474.5pF
R: 6.023 k ohms
W: 53.720 grams

Submerging potted pickup in alcohol at 150F for 30 mins, 1 day later

L: 2.462H
C: 174.25pF
R: 6.068 k ohms
W: 53.000 grams



100kHz bode plot before potting, after, and then after alcohol submersion:






Extreme little microphonics: 


Slight microphonics: 


Substantial microphonics: 

[reTrEaD]

Dec 9, 2019 10:47:28 GMT -5 antigua said:

As would be expected, while the pickup is still cold, the wax mostly condenses around the outside of the pickup, and during that time the capacitance is unchanged, but once the pickup reaches the temperature at which the wax melts, the wax permeates the coil, releasing air bubbles

Would anything be gained by pre-heating the coil (for instance, in an oven) to the same temperature as the melted wax?

[antigua]

Dec 9, 2019 12:14:40 GMT -5 reTrEaD said:

Dec 9, 2019 10:47:28 GMT -5 antigua said:

As would be expected, while the pickup is still cold, the wax mostly condenses around the outside of the pickup, and during that time the capacitance is unchanged, but once the pickup reaches the temperature at which the wax melts, the wax permeates the coil, releasing air bubbles

Would anything be gained by pre-heating the coil (for instance, in an oven) to the same temperature as the melted wax?

I don't think it makes much difference, the end result is the same. Once the copper wire reaches the melting temp of the wax, the coil rapidly uptakes the wax, about 0.8 grams worth in the case of my 8k turn Strat pickup. 

I think there is a benefit to heating the pickup in the oven afterwards, just above the melting of the wax, as a means of removing excess wax. It looks sparkling clean. 

[antigua]

I was expecting the can of alcohol to be evaporated this morning, but interestingly the remnant wax dried on the surface, sealing in the alcohol in the can. 

[antigua]

An update, I tried de-potting a Chinese humbucker and a Seymour Duncan SSL-1, which already had low capacitance to begin with, but the capacitance of those pickup didn't drop at all, but I did get some good data. 

The pickups were heated in ethanol at 150 degree Fahrenheit, so the alcohol was boiling off, but the water in the double boiler wasn't. 

Seymour Duncan SSL1-N, exposed coils
initial values:
 L: 2.517H
 C: 104.93pF
 R: 6.631k ohms
1 hour after heating in alcohol for 1 hour:
 L: 2.52H
 C: 128.39pF
 R: 6.660k ohms
2 days after heating in alcohol:
 L: 2.528H
 C: 107.98pF
 R: 6.597k ohms


Chinese Humbucker, taped coils
initial values:
 L: 3.421H
 C: 137.98pF
 R: 7.484k ohms
1 hour after heating in alcohol for 1 hour:
 L: 3.414H
 C: 150.32pF
 R: 7.500k ohms
2 days after heating in alcohol:
 L: 3.398H
 C: 138.81pF
 R: 7.424k ohms



Both pickups increased in capacitance by about ~15% afterwards, because the alcohol has a much high dielectric value compared to air or wax, but the increase in capacitance was very small compared to the increase in capacitance of my homemade pickup, a 300% increase in capacitance as compared to 15%. The difference is most likely that the SSL-1 and Chinese humbucker were machine wound with a much higher tension than my hand tensioned pickup, so my coil was able to accept a lot alcohol, causing the capacitance to become a lot higher before it evaporated out. I believe that my hand wound coil also accepted and then released a lot more wax, as well.

The Chinese humbucker's coils are taped over with some sort of vinyl tape, and that might have helped hold any wax in. Pulling the tape away, there is visible traces of wax, so the pickups were wax potted. Removing the tape prior to submersion might have increased the odds that was would come out, but I was interested in seeing how much wax might come away from the pickup "as is". If I remove the tape, I might get better results, but another problem is that the 150 degree alcohol managed to mar the surface of the plastic bobbin, so there's already pretty much no hope that anyone would want to submerge a plastic pickup in alcohol, no matter what. I suspect that, as a means of modifying a pickup, it only has application with vintage style Fender pickups, which temperature sensitive plastic parts. 

Even though the capacitance of the two production pickups was ultimately unchanged, the homemade pickup with the lower tension coil came closer to the pre-potting capacitance of 142pF. It was 174pF, and dropped down to 152pF, so the extra hour in heated alcohol reduced the capacitance by another 22pF, ending up at 10pF above where it had been prior to wax potting.

initial C, after first depotting:       176.25pF
1 hour after heating in alcohol again:  454.1pF
2 days after heating in alcohol again:  152.53pF

These results suggest that the machine wound pickups have much more tightly wound coils, and so while it seems that my test pickup was fully wax saturated in under two minutes it might be the case that a machine wound pickup would require more time, or even vacuum wax potting in order reach saturation. The potential for wax to impact the capacitance, and the potential to remove it, depends on how tightly the coil is wound, and unfortunately, these and most production coils are probably wound rather tightly for a different reasons, such as reducing microphonics independent of wax potting, and to ensure that the coil never stick out past the edges of the bobbin / coil former.

I have some production pickups that have rather fat coils though, particularly the DiMarzio single coils, which barely fit covers over the top.  I might put them through this test, as it might be that they're looser wound with a lot of wax too, or it could be that they just have thicker insulation coats on the magnet wire, and that's what accounts for their thickness. That testing would be limited in value though, since the majority of production pickups appear to have relatively tight coils, and would seem to be almost modifiable, via heat and soaking. 

The microphonics of the pickups was more or less unchanged. Both pickups put out double the noise floor voltage because and after the heated alcohol soaking. The SSL-1 showed more high frequency microphonics afterwards, but at the same overall voltage, and that might have been due to the soaking having loosened up the outermost windings of the coil slightly, which are the most liable to cause microphonics,as they are are more free to move about than the windings deeper within the coil. 




I'm still interested in trying other solvents, but I get the feeling that unless the coil is simply unwound, the wire cleaned, and then the pickup rewound, the wax is effectively inaccessible. Based on these experiments though, it's pretty clear that the wax could be removed if the pickup were carefully unwound, cleaned, and then rewound, because the loose wire is easily cleaned in heated alcohol, possibly or maybe even just heated soapy water.

The idea of depotting a pickup is based on the premise that potting the pickup changed the pickup in a meaningful way to begin with, but as is seen, neither the microphonics nor the capacitance changes to an extent that a guitarists would ever notice in practice, so it's more the thought that counts, removing the wax for its own sake, to see if the pickup can be restored to pre-wax potted condition. 

[pablogilberto]

This is very interesting antigua

I'd like to know if you were able to demistify the best way to do wax potting so that the microphonics will be eliminated while keeping the added capacitance as low as possible?

Do you think that experimenting with kind of wax (beeswax vs paraffin or combination of both) is not worthwhile?

Thank you!

[antigua]

Jun 22, 2020 6:00:44 GMT -5 pablogilberto said:

This is very interesting antigua

I'd like to know if you were able to demistify the best way to do wax potting so that the microphonics will be eliminated while keeping the added capacitance as low as possible?

Do you think that experimenting with kind of wax (beeswax vs paraffin or combination of both) is not worthwhile?

Thank you!

Not really, the problem is that once the copper wire reaches the melting point of wax, the wax permeates the coil very rapidly. I'm planning an experiment to track the capacitance with respect to time. I'll connect the LCR meter to the pickup while it's in the process of potting.

If a person was really careful, they could watch for the moment when bubbles emerge, that's when air starts releasing from the coil, and they could pull it out of the wax real fast, and and that point there might be partial penetration. The outside of the coil would be encased, but the inner winding somewhat free of wax.

Another method that might work is to dip the pickup in wax and remove it quickly, in let's say, fifteen seconds. There would be little to no penetration at that point, but the wax would be caked around the outside of the pickup. Put the pickup in an oven at 170F degrees, the wax will melt, and the copper coil will also heat up and absorb some amount of the wax. The total amount of penetration should be minimal, but possibly enough to eliminate microphonics. That would only work for a fiber bobbin pickup, I think  plastic coils would possibly deform at 170F. Maybe just leaving the pickup in hot, direct sunlight would work too. 

[pablogilberto]

Jun 22, 2020 15:31:33 GMT -5 antigua said:

If a person was really careful, they could watch for the moment when bubbles emerge, that's when air starts releasing from the coil, and they could pull it out of the wax real fast, and and that point there might be partial penetration. The outside of the coil would be encased, but the inner winding somewhat free of wax.

Is this similar to a half wax potting? Meaning the inner windings will be free from wax.

Is it correct to assume that the microphonics reduction will be the same since the outer windings causes more noise?

How about vacuum potting? Do you have any resource about that? Or have you performed any experimentation?

Thanks!

[antigua]

Jul 7, 2020 6:36:36 GMT -5 pablogilberto said:

Jun 22, 2020 15:31:33 GMT -5 antigua said:

If a person was really careful, they could watch for the moment when bubbles emerge, that's when air starts releasing from the coil, and they could pull it out of the wax real fast, and and that point there might be partial penetration. The outside of the coil would be encased, but the inner winding somewhat free of wax.

Is this similar to a half wax potting? Meaning the inner windings will be free from wax.

Is it correct to assume that the microphonics reduction will be the same since the outer windings causes more noise?

How about vacuum potting? Do you have any resource about that? Or have you performed any experimentation?

Thanks!

Potting just the outside of the pickup eliminates nearly all of the microphony, because they are the loosest winds, and the most exposed to changes in air pressure. The inner windings can still move as a result of physical shock, like tapping on the pickups with a guitar pick, but that's a lot less likely to associate with noisy feedback. 

I don't think there is any validity to vacuum potting. I've done multiple tests now and it's clear that the coil is also fully penetrated, at least with Strat pickups. It's possible that a PAF bobbin, if it's air tight in the center, might not release air, and a vacuum could suck that air out, but once the copper is hot, it absorbs wax, which is very oily, by capillary effect. Heated liquid paraffin doesn't have the surface tension of water, so it can't be imagined as a water-like reaction.

The only way to know if a pickup has been fully penetrated, without cutting it open and ruining it, is by observing the capacitance, and since it appears that probably zero pickup makers care at all about the capacitance, I think it stands to reason that no pickup maker would actually know whether or not wax potting was actually necessary. Regardless, to say that a pickup is vacuum potted justifies charging more money, so whether it has any practical effect or not is, at best, a secondary feature of the practice.

I'm planning an experiment for this weekend, I'll track the change in capacitance with respect to time, Ill have the LCR meter connected to the pickup while it's in the wax, and that will give some insight into how quickly the wax permeates the coil.