Post by antigua on Apr 26, 2020 22:35:17 GMT -5
I did a wax potting test similar to this a few months ago guitarnuts2.proboards.com/thread/8739/wax-potting-experiment-capacitance-microphonics , but one shortcoming with that test was that the precise moment of the coil saturating wasn't clear. I could have swore I did a more precise test, but I couldn't find it, so I just did it again, and these are the results.
This test starts with an unpotted pickup that I bought from TDPRI user kingvox, who made them, dipping the pickup in paraffin heated to about 180F for some length of time, and then recording the capacitance, and the level of noise generated by physically impacting the pickup.
One interesting thing I realized while doing this, this time around, is that the wax potted pickup regains some of the sensitivity to physical impact when the wax is heated and in a liquid state internally, so I had to let the pickup cool between tests in order to make sure it cooled to a solid state, but that in turn meant that the pickup had to re-heat when I dipped it into the wax again. Therefore, what took six minutes through heating and cooling might only take three minutes with continuous heat.
30 seconds of dipping, the pickup is still colder than the wax, so it forms a shell around the pickup.
Partial penetration; note that in some areas the wax soaked into the coil, where as in others wax is still hardened on on the outside of the coil. This is at the 2:30 mark, capacitance is 131.54pF, about the half way point between 107pF and 164pF.
After 15 minutes, not fully cooled:
So it appears that the process of wax penetration is very sudden, and not really a slow process. First, the wax, held at ~180F is a lot hotter than the 70F room temp pickup, so the wax hardens against the outside of the pickup. Once the bobbin and coil reach a temperature at which wax melts, which is somewhere between 115F and 150F, the wax around the pickup, and particularly the coil, becomes liquid. Wax, being very oily, seeps into the coil windings at that point. The capacitance of the coil also increases, since the dielectric value of air, 1, is much lower than that of paraffin (2.2 - 4.7). The coil begins with a capacitance of 107pF and between 1 minute and 30 second and 4 minutes, it jump up to 161pF, with a mid-point of 131pF at 2 minutes 30 seconds, but because it was cooled and reheated three or four times in between, had the pickup been left submerged continuously, it might have happened in half that time. The capacitance increased slightly from eight minutes to fifteen, but it appears that by this point the coil was effectively saturated through and through.
Regarding the microphony / physical impact testing, I hit the pickup with a wooden spoon in order to get some sort of mechanical voltage from the pickup. I have to his the pickup, because methods such as "talking into the pickup" or introducing sound waves alone is not sufficient to get any measurable voltage that is distinct from ambient noise. Not only that, but I have to use an overdrive pedal to punch up the gain as well. The impact voltage follows the capacitance and visuals rather close; when the capacitance was half, and the coil appeared to be half penetrated, a good voltage could still be had from striking the pickup with a wood spoon, but once the capacitance reached the peak of ~160pF and the coil wax fully liquefied around the coil, the voltage from physical impact became very small, similar to the noise voltage, even with signal gain.
This test starts with an unpotted pickup that I bought from TDPRI user kingvox, who made them, dipping the pickup in paraffin heated to about 180F for some length of time, and then recording the capacitance, and the level of noise generated by physically impacting the pickup.
One interesting thing I realized while doing this, this time around, is that the wax potted pickup regains some of the sensitivity to physical impact when the wax is heated and in a liquid state internally, so I had to let the pickup cool between tests in order to make sure it cooled to a solid state, but that in turn meant that the pickup had to re-heat when I dipped it into the wax again. Therefore, what took six minutes through heating and cooling might only take three minutes with continuous heat.
30 seconds of dipping, the pickup is still colder than the wax, so it forms a shell around the pickup.
Partial penetration; note that in some areas the wax soaked into the coil, where as in others wax is still hardened on on the outside of the coil. This is at the 2:30 mark, capacitance is 131.54pF, about the half way point between 107pF and 164pF.
After 15 minutes, not fully cooled:
So it appears that the process of wax penetration is very sudden, and not really a slow process. First, the wax, held at ~180F is a lot hotter than the 70F room temp pickup, so the wax hardens against the outside of the pickup. Once the bobbin and coil reach a temperature at which wax melts, which is somewhere between 115F and 150F, the wax around the pickup, and particularly the coil, becomes liquid. Wax, being very oily, seeps into the coil windings at that point. The capacitance of the coil also increases, since the dielectric value of air, 1, is much lower than that of paraffin (2.2 - 4.7). The coil begins with a capacitance of 107pF and between 1 minute and 30 second and 4 minutes, it jump up to 161pF, with a mid-point of 131pF at 2 minutes 30 seconds, but because it was cooled and reheated three or four times in between, had the pickup been left submerged continuously, it might have happened in half that time. The capacitance increased slightly from eight minutes to fifteen, but it appears that by this point the coil was effectively saturated through and through.
Regarding the microphony / physical impact testing, I hit the pickup with a wooden spoon in order to get some sort of mechanical voltage from the pickup. I have to his the pickup, because methods such as "talking into the pickup" or introducing sound waves alone is not sufficient to get any measurable voltage that is distinct from ambient noise. Not only that, but I have to use an overdrive pedal to punch up the gain as well. The impact voltage follows the capacitance and visuals rather close; when the capacitance was half, and the coil appeared to be half penetrated, a good voltage could still be had from striking the pickup with a wood spoon, but once the capacitance reached the peak of ~160pF and the coil wax fully liquefied around the coil, the voltage from physical impact became very small, similar to the noise voltage, even with signal gain.
