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Topic: Potentiometer for Tonemaster |
Frank James Pracher
From:
Michigan, USA
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Posted 14 Feb 2015 8:34 pm |
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I'm going to put this here as opposed to electronics because I think lap steel/non pedal players will appreciate what I'm getting at.
The volume pot in my beloved 1940 Oahu Tonemaster is getting really scratchy. I'm going to give it another cleaning but this thing is getting tired.
Does anyone have any recommendations for a new 500k pot with a good "feel"? The new pots I've tried are stiff, and the taper feels all wrong. I use the volume control constantly for swells and what not. The ones I've tried have just been the off the shelf ones at the guitar shop.
Thanks in advance
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"Don't be mad honey, but I bought another one" |
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Stephen Cowell
From:
Round Rock, Texas, USA
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Frank James Pracher
From:
Michigan, USA
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Posted 14 Feb 2015 9:18 pm
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Thanks Stephen, sources for pots abound. I'm kind of hoping to hear from folks who have tried some and found ones they like.
"Buy and Try" is always an option but could get pricy pretty quick.
_________________
"Don't be mad honey, but I bought another one" |
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Tom Pettingill
From:
California, USA (deceased)
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Jack Hanson
From:
San Luis Valley, USA
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Posted 15 Feb 2015 8:22 am
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This post caught my immediate attention. It piques my interest for a number of reasons:
As Frank explained above, I also favor using the volume control for swells and similar effects. On some of my instruments it is nearly impossible due to the "tightness," for lack of a better term, of its volume pot.
One example: A while ago I acquired a '50s Gibson Century Deluxe that was fitted with the wrong pickup. Here's a link to that story:
http://bb.steelguitarforum.com/viewtopic.php?t=275422&highlight=
I installed a new custom wound Sentell P-90 and three new pots, all of which were CTS 500K audio taper. The two tone controls operate okay. The volume control, however, tapers off gradually from the 10 position to about the 7 position, then abruptly cuts off nearly altogether. It's also very, very tight, making volume swells all but impossible. What type of pot should I install as a volume control to best achieve a more gradual taper and a looser feel?
It is my understanding that the most common pots used for guitar applications are either linear or audio taper, and either 250K or 500K resistance. How does one choose which type to use for any given application? Is it basically trial and error, or is there a universal guideline that should be followed?
A wiring diagram for early Gibson Ultratone and Century models specify 500K reverse audio taper pots. What is "reverse audio," who makes them, and where can they be obtained? |
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Tom Pettingill
From:
California, USA (deceased)
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Posted 15 Feb 2015 10:30 am
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| Quote: |
| What is "reverse audio," who makes them, and where can they be obtained? |
Reverse audio taper is just that, a reverse version audio taper. If you look at this spec sheet I linked to, you can see the three comparison graphs for each, A2 = Audio, B0 = linear, and C2 = reverse audio. http://www.mouser.com/ds/2/54/PDB241-GTR-57705.pdf
The Bourns GTR series are very low friction and also come in reverse taper with both solid shaft and knurled 18 spline shafts. Note that the 18 spline might require new knobs as CTS is a finer 24 spline configuration.
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George Piburn
From:
The Land of Enchantment New Mexico
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Jack Hanson
From:
San Luis Valley, USA
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Posted 17 Feb 2015 12:32 pm
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Thanks so much, Tom and George. That is great information, and exactly what I was looking for.
Still seeking clarification on the following point, however:
I'm under the impression (perhaps erroneously) that the choice of pot, whether 250K or 500K, is determined by the resistance of the pickup(s). Is there any general rule-of-thumb to follow here? Or, is it basically try 'em both and select the one you think sounds the best? |
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George Piburn
From:
The Land of Enchantment New Mexico
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Posted 17 Feb 2015 12:52 pm Which One with which
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General Rule of Thumb is 250K with single coil and 500k with Humbucking.
Tom can confirm this better than me.
250k typically give a slightly darker tone, a single typically is brighter than a HB.
I use 250k Linear (B Curve) on both volume and tone with our VintageSpec Single coils. with a .047 5% orange drop cap.
Audio Taper will might be better if you are doing the Swell thing all the time.
Hope this helps some 
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Tom Pettingill
From:
California, USA (deceased)
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Posted 18 Feb 2015 10:26 am
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| Jack Hanson wrote: |
... Still seeking clarification on the following point, however:
I'm under the impression (perhaps erroneously) that the choice of pot, whether 250K or 500K, is determined by the resistance of the pickup(s). ... |
Resistance in of itself does not have anything to do with how bright or dark a pickup may be. The size, shape, and number of winds of a coil determine its voice. Resistance can be a useful tool when comparing two pickups of the same construction and coil wire gauge, but not when comparing dissimilar pickups. The resistance of a pickup is a result of the wire size and its length. Take an old Rick Horseshoe for example. It was wound with a thicker 38 gauge wire and because of its size, and the fact that thicker wire means you can't get as much length on there as a smaller wire, you end up with a coil that is often below 2K.
| Quote: |
| General Rule of Thumb is 250K with single coil and 500k with Humbucking. |
That is the general rule of thumb, but there are certainly exceptions. Coil size and shape play a big part in a pickups voice and resonant frequency / brightness. Taller coils like Fender single coils tend to be overall brighter and a P90 with its short and fat coil tends to be lighter in the highest frequencies and more mid focused. In this case, a 500K pot is often the favored P90 choice.
For caps, you generally see .047 used for brighter single coils and .022 for a darker pickup like a humbucker. While this is the general practice, for some players a brighter cap may fit their preferences better. As an example, if you find that you never use or don't like the tone when rolled all the way off, you may find that a .033 or a .022 gives you more useful range of adjustment as it rolls off less highs over a broader range.
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Jack Hanson
From:
San Luis Valley, USA
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Posted 19 Feb 2015 8:11 am
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Thanks again, George and Tom.
That's great information and definitively answers my question. I plan to order a variety of pots and use my old Gibson Century Deluxe with the new Sentell P-90 pickup (4.6K) as a guinea pig for experimentation.
My other 6-string Gibson lap steels, which all have their stock wide-oval or P-90 pickups, all measure between 7.3K and 9.9K. No two of them sound exactly the same, but they all sound good to my ear.
Tom's answer explains why the horseshoe pickup in my B-6 Ric measures only about 1.8K, and it's far and away the best-sounding pickup on any of my instruments. |
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George Piburn
From:
The Land of Enchantment New Mexico
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Brad Bechtel
From:
San Francisco, CA
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Posted 21 Feb 2015 10:20 am
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Moved to Electronics.
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A web site devoted to acoustic & electric lap steel guitars |
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