Trainwreck express pots

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RJ Guitars
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Re: Trainwreck express pots

Post by RJ Guitars »

The guys at CTS will make pots in any taper you want - but you have to order a minimum quantity and typically that is some number like 100 each. You might be stuck with inventory for a long time!

Can we assume that taper only effects the position the knob will be at when a specific setting is pleasant to our ears or is there also some other mystical thing happening that actually changes what we hear?
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Re: Trainwreck express pots

Post by Mark »

Alpha pots from Memory have a 15% taper and the CTS pots I've encountered have a 10% or less taper. I don't think the volume control should be behaving like a switch, that doesn't seem right.
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Mark Abbott
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Re: Trainwreck express pots

Post by Mark »

This is a little off topic but it deals with Glen's comments about requiring a long cable to get rid of the fizz. Though it would be just as easy to wire a cap across the input jack.

http://zerocapcable.com/?page_id=231

http://www.undertoneaudio.com/products/ ... ment-cable

Any thoughts or experiences?
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Re: Trainwreck express pots

Post by geetarpicker »

The 10% pots here are refering to the taper. So take a 1meg pot and turn the shaft to the half way point. Then measure the ohm value with a meter between the center lug and an outside lug, then from the center lug to the other outside lug. One reading should be about 900k, and the other 100k being the 10% we are talking about. So you then have a pot where the resistance only ramps up to 100k by the time you are half way up, then the other 900k of difference happens between 1/2 and full up. With the Express circuit you should then have a volume control that ramps up much more gradually than say a 30% taper or god forbid a linear taper. The pots in my original '85 wreck ramp up so slowly the amp isn't all that gainy until at least 1/2 way up. The pots in that are probably more like 8% taper TRWs. All and all the controls are much easier to work with with 10% taper pots, and the amp becomes more versatile as a result.
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Re: Trainwreck express pots

Post by geetarpicker »

In regards to using longer cables to reduce the fizz. I tried simulating this effect with a little box with a small cap, but it just never worked as well as a longer cord. I think there is more going on than just a little added capacitance, so back to longer cables for me.
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Re: Trainwreck express pots

Post by Mark »

Glen thanks for your reply, do you find your clean tones suffer from the loss of highs or do the caps across the volume control restore some of the highs?

Anything special about the cable itself?
There was mojo about curly cables some years back saying they added inductance.
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Re: Trainwreck express pots

Post by Roe »

geetarpicker wrote: Tue Sep 12, 2017 6:02 pm In regards to using longer cables to reduce the fizz. I tried simulating this effect with a little box with a small cap, but it just never worked as well as a longer cord. I think there is more going on than just a little added capacitance, so back to longer cables for me.
the distributed capacitance of a cable is supposed to differ from a mere capacitor, although I don't understand how
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nworbetan
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Re: Trainwreck express pots

Post by nworbetan »

My thoughts about the distributed capacitance is that it's acting like a (nearly) infinite number of low pass RC filters with infinitesimally small capacitance to ground coupled by infinitesimally small resistors. If anyone knows the math well enough to explain how two 9k ohm + 50uF filters would perform compared to one 18k + 100uF filter, I'd be interested in that.

I just bought some fancy pants silver plated PTFE shielded cable a few weeks ago, and the first project that needed it happened to need about 13 inches, which my Fluke said was between 40 and 50 pF (which also included the capacitance of the meter leads in parallel with the short piece of cable). I didn't care enough at the time to measure the other (super cheap) shielded cable I have laying around, but maybe if high cable capacitance is something that can be beneficial, it might be worth looking a little more closely at?
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Re: Trainwreck express pots

Post by Mark »

I have tried leads with high capacitance but I've found I lost highs in my Fender style amp without being able to get a good clean tone. I imagine a 500pF could change that though.
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Mark Abbott
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