CTS pots.

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Re: CTS pots.

Postby alexjones » Thu Mar 28, 2013 6:56 pm

Norm,
Sorry for the delay. Thanks for all the great information! You got me even more excited about putting unpotted pickups in my 59 RI. I still haven't made the order yet with TV Jones. I will do it sometime soon - but it's not exactly at the top of my priority list. Maybe within a few months. I will post back some results when I get them installed. Take care!
Alex
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Re: CTS pots.

Postby Norm » Thu Mar 28, 2013 8:18 pm

Well, first I had my opinion but I'm a curious kinda guy and the internet is such a tool I decided to look into it, ask people and learned a lot in the process. I found my original opinion was skewed (wouldn't be the first time) but I've never been afraid to admit it being wrong when I was and share information as I found it

Good luck with your project
...that's how it looks to me...The opinion expressed above is my own and does not necessarily reflect the views of this station. Your mileage may vary...

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That should do it.
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Re: CTS pots.

Postby Mike Detlefsen » Sat Mar 30, 2013 1:23 am

This isn't directed at Norm, who was quoting someone:

"Basically mechanical vibrations from the guitar shake the coils in the pickup. These small movements in the coil wires change the positional relationship between the coils wires and the moving strings. When you wax the coils, you kill this."

This sounds really bogus to me, as far as affecting tone. It's the magnetic field created by the coils that generates the sound. Any miniscule vibration shouldn't affect the individual windings that much, tone-wise[quote][/quote]. Coils are generally wound pretty snugly. I wind my own coils these days, and Ive never heard any perceptible difference between potted and un-potted coils, as far as tone goes. Potting may reduce feedback, but that's about it.

I'm in the process of setting up to wind two Gibson-type humbuckers to 4K instead of 8K resistance. I think I'll pot one and not the other and take some measurements and see if the frequency output is any different.

Mike
Last edited by Mike Detlefsen on Sat Mar 30, 2013 12:30 pm, edited 1 time in total.
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Re: CTS pots.

Postby Norm » Sat Mar 30, 2013 8:42 am

I can't speak for the difference in actual tone between potted and unpotted coils.

As far as the idea of a distinctive type of feedback due to loose coils...I'd say that's well within the realm of possibility. Also, some pickups are more microphonic than others. I can't swear by it but it is likely that unpotted pickups could/would be prone to that condition. I worked a long time in a guitar store and you get quite a cross section of merchandise to analyse.

The only way to be sure would be to find a really microphonic, high squeal feedback, guitar and see if potting cures it.

The makers who pot their coils do it for a reason. It is a bit time consuming and mildly labor intensive process and as we all know, time is money.
...that's how it looks to me...The opinion expressed above is my own and does not necessarily reflect the views of this station. Your mileage may vary...

Audio samples: http://www.youtube.com/user/acountrygent/videos
That should do it.
Norm
 
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Re: CTS pots.

Postby Mike Detlefsen » Sat Mar 30, 2013 1:32 pm

The issue may very well be more complex than it appears. For instance, when we talk of potting a coil, are we talking about just the coil, or are we talking about potting the entire pickup? I've seen it done both ways. If potting the pickup reduces or eliminates the feedback issue, it's possible that the back plate the coils and magnets are mounted on was stopped from vibrating and causing the feedback. So one could stiffen that plate and stop feedback without potting the coils. Or it could be loose magnets that get fixed in place by the wax.

It's not really as simple as it sounds. And I've found that pickup manufacturers are just as subject to hearing what they expect to hear as anybody else (including me). That's why I like to see charts and graphs.

Mike
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Re: CTS pots.

Postby Norm » Sat Mar 30, 2013 3:22 pm

MORE stuff to jaw about instead of practice! :D
...that's how it looks to me...The opinion expressed above is my own and does not necessarily reflect the views of this station. Your mileage may vary...

Audio samples: http://www.youtube.com/user/acountrygent/videos
That should do it.
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Re: CTS pots.

Postby Mike Detlefsen » Sat Mar 30, 2013 4:33 pm

I can do both, sometimes simultaneously. :)

Mike
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Re: CTS pots.

Postby Brian Ingram » Thu Aug 01, 2013 7:43 pm

Norm wrote:...

A well made pickup might not need potting as cited here:

Any guitar with a pickup that is microphonic but otherwise a good sounding pickup is a good candidate for potting. If your pickups aren't microphonic then there is little point to potting them ...


We probably should have ended the conversation there, as it seems to be the most solid advice.

Mike Detlefsen wrote:"Basically mechanical vibrations from the guitar shake the coils in the pickup. ... When you wax the coils, you kill this."

This sounds really bogus to me, as far as affecting tone. ...


You were right Mike that this person's statement is bogus if they meant that the movement they described creates highs.

Here's what's happening:
A pickup is a coil of wire in a magnetic field (provided by the magnet(s) and extended/directed by the polepieces). Now if a magnetic field moves through/across a coil of wire, a current will be induced in the coil. Alternatively, if you physically move a coil through a magnetic field, you will also induce a current in the coil. That is, if the field is moving or if the coil is moving, it's all the same and a current is induced.

Normally, the coil doesn't move. Instead, the ferrous metal in the strings (which sit in the pickup's magnetic field) move when you pluck them, and that disturbs the pickup's magnetic field, which is the same as the field moving through the coil, and thereby creating an output from the pickup.

So how would the pickup windings move at all? As Mike noted, it would seem normal winding tension is sufficient to keep the windings from moving... and it is, as far as I can tell. The pickup would have to have very loose components/windings, and would have to be near screaming guitar amps in most cases to get any audible feedback.

That said, I once saw Elvis Costello in concert who had one of those super-cheesy 60's Japanese knock-off guitars during one song. He held the guitar top near his face and sang/screamed and the ultra-microphonic pickups amplified his voice (in a garbled manner) through a guitar amp. But that's so rare I've only seen pickups that microphonic once.

Really, reducing feedback was probably an after-thought originally. The transformers used in guitar amps work under the same principles as pickups and are usually sitting much closer to loud speakers. But most guitar amp transformers aren't potted... why? Because potting is more expensive, and is largely meant to keep moisture out. So expensive transformers might get potted in epoxy, varnish or a tar-like substance, but are rarely wax-potted because many waxes absorb moisture over time, which defeats the main purpose of potting.

So if the pickup's sound isn't changed by feedback vs no-feedback, then what changes between potted & unpotted?

I don't know for sure, but I'll tell you what I think is most-reasonable: all coils (and all electronic wiring in general) have stray capacitance; that capacitance from one end of the coil to the other is increased when wax (or other potting material) is present over an unpotted pickup. This is like having a very small (say 10-100pF) cap bridging the two output wires of your pickup. That rolls off some amount of high end.

There is a mathematical formula to find the capacitance of a capacitor based on its physical properties, including what material is separating the conductors that form the cap. Air results in the lowest capacitance when you change only that material separating the conductors. Wax has a higher dielectric constant, and therefore results in a higher capacitance.

However, I'm skeptical when it comes to describing how much effect this will have on any pickup's sound. Guitar cables, amp wiring, different tube types present varying amounts of stray capacitance, so any of them could have as much, or more, impact on your guitar's tone.

Additionally, any pickup maker knows there are a lot of competing variables to any pickup design, and changing any one of them can give you a darker or brighter or midrangy-er or louder or softer pickup. And your amp, speaker, control settings, effects, etc also shape the guitar's tone... so is that stray capacitance really that big of an issue?

As with everything sound-related, tone is in the ear of the beholder. You'll have to try both ways (if you're worried there's a difference) and reach your own conclusions.
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