Why does this new Gibson 500k pot have no taper?

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Why does this new Gibson 500k pot have no taper?

Postby 71Rcode on Sat May 07, 2011 4:14 pm

I was about to order an RS kit for my '76 LP custom (scratchy pots) when I decided to look through my parts box first. I found 4 brand new "Gibson" 500k audio pots - so I wired the LP up this morning the same way. BTW, have highorder pickups in there. Love 'em.

My problem. The tone volume has very little taper = it's full on at 10 and then nearly inaudible at 1-5. And the volume drops off sharply at 8 and below. The original pots had a nice taper to them, but were just too scratchy to keep in there.

Did I make a mistake? I wired her up the same way, which is exactly like an '06 LP classic I've got. And even switched the tone/volume pots (bridge pickup), as the new Gibson tone pot had a nice, linear taper to it. When I put that tone pot in the volume position (neck), she lost all the taper.

Thanks :D

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Re: Why does this new Gibson 500k pot have no taper?

Postby Vortexion on Sun May 08, 2011 10:00 am

This is what I think is going on:

In the good old days, manufacturers used proper Log taper pots (which take skill to manufacture, and are thus expensive). Then - I don't know exactly when - some bright spark of an accountant came up with the idea that, instead of trying to make a carbon track with a smooth log taper, it would be much easier and cheaper to make a very crude approximation of it by taking two linear tracks of different values and bunging them end to end. This is what we now get sold when we buy a so-called "Audio Taper" pot.

If you have a look at this diagram, you'll see that the two are very different animals:

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The blue curve is a proper log pot: nice and smooth all the way.
The red line (labelled "commercial log" in the diagram) is the cheapo Audio Taper type. Not exactly an accurate approximation, is it? :roll:

I suspect that your brand new Gibson replacement pots are this latter type.

Fortunately, there is a way to create your own genuine log pots: the curve you achieve will be be almost a perfect match of a log taper, and you'll even be able to customise the slope to suit your own taste! This is what you do:

1) Buy a LINEAR pot of the value you want.

2) Solder a resistor between the pot's wiper tag and the bottom (ground) tag. To mimic a log taper, the value of this resistor should be approx 10% of the value of the pot. So if you've got a 500k pot, use a 50k resistor (in reality, the closest popular values you will be able to buy are 47k or 51k - that's fine: it's not critical).

Wanna experiment with different slopes? Here is an online calculator tool (it's a Java Applet) that shows you the effect of using different resistor values:

http://www.mindspring.com/~clist/PotGraph.html

Ignore the "Input Voltage" box - it's not relevant. Just type your values into the "Pot resistance" and "Input Resistor" boxes and you'll see the curve of the red line change its shape.

Have fun! :thumbsup:
Last edited by Vortexion on Sun Dec 30, 2012 6:03 pm, edited 1 time in total.
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Re: Why does this new Gibson 500k pot have no taper?

Postby 71Rcode on Mon May 09, 2011 4:24 pm

Thanks, Vortexion. Good stuff. I concur with your hypothesis, sir! Thanks for taking the time to explain all of that.

And I will get a couple new volume pots/caps on order from RS Guitarworks.
* Superpots (may try them for the volumes)
* Caps --- either the Jensen, Luxe Bees or the RS house brand
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