Upgrading Your Electronics Part 3: Potentiometers

This is the third article in the “Upgrading Your Electronics” series and this one is going to be an epic journey into the world of potentiometers.  If you haven’t read the previous two articles, you can find them here: Part 1 and Part 2.  These articles are meant to provide a foundation of knowledge about guitar electronics that continues to build with each subsequent article and by the time we’re done, you should know exactly how to choose the right components to upgrade your guitar…. or you may be so fascinated with electronics that you hit the books to become an electrical engineer.

CTS 500k Vintage Taper Split Shaft Pot

Potentiometers.  So many syllables, let’s just call them pots.  Pots are fairly straight-forward components yet there seems to be unending discussions about which ones are the best to use for volume and tone controls.  It’s not that hard to figure out as long as you don’t over-analyze them, but that can’t be helped when you’re on a tone quest (as most of us are).  So let’s first go over what a pot does, then we’ll look at the different types of pots.

Most guitars have at least one volume control and at least one tone control.  These controls are pots that are wired in a way that they affect the signal from the pickups as it travels to the output jack.  Pots, in the simplest terms, are variable resistors that use the sweep (the process of turning the knob) to adjust the amount of resistance placed into the circuit.  For volume pots, the resistance affects the strength of the signal from the pickups, which translates into the output volume through an amplifier.  If you start with the pot fully clockwise, there is no resistance in the signal so the volume from the amplifier is full.  As you turn the pot counter-clockwise, resistance is gradually introduced to the signal which reduces the output to the amp, thus lowering the volume.  Once the pot is turned fully counter-clockwise, the signal is completely blocked and the volume through the amp is zero.

The tone control works essentially the same way, but it is wired in such a way that the variable resistance affects the output frequency, not the output volume.  When using a capacitor in the circuit, it dictates which frequencies are affected by the sweep of the pot.  Most guitars use capacitors in the 0.010uf – 0.047uf range, which affects the higher frequencies in the signal (not to worry, we will dive deeper into capacitors in the next article).  So with the tone control, if you start with the pot fully clockwise, there is no resistance in the signal so the signal is full spectrum.  As you turn the pot counter-clockwise, resistance is gradually introduced to the signal and the high frequencies are reduced.  Once the pot is turned fully counter-clockwise, the high frequencies are completely blocked while the lower frequencies are unaffected.  This makes the sound darker, muffled, and less dynamic.

This was meant to be a simple explanation to get an idea of how the volume and tone pots work.  With that done, now let’s go over the different types of pots.  I’m sure we can come up with some clever “pots” but for this discussion we will focus on the three types used in guitars: audio taper, linear taper, and vintage taper.  The taper refers to the sweep I mentioned above.  It’s how smoothly the resistance is introduced into the signal.  Let’s take a look at the following chart:

To make things easier to understand, let’s start with the linear taper pot, noted as “B” in the chart.  Linear taper is designed to be just that – linear across the sweep of the pot.  At 50% rotation of the pot, 50% of the resistance is affected.  Audio taper, noted as “A” in the chart, has an interesting curve to it’s sweep.  At 50% rotation of the pot, about 75% of the resistance is affected.  Now, you may be wondering why anyone would want to use an audio taper pot instead of a linear taper pot since linear should mean a smooth sweep?  With typical passive pickups, volume and resistance don’t have a 1-to-1 relationship so with a linear taper pot the volume will not have a true linear sweep.  When using a linear taper pot for a volume control, you can expect a gradual increase in volume from 0% to about 60% then a big jump in volume from 60% to 100%.  To compensate for this jump, the audio taper pot was developed with a sweep that provides a more linear volume output.  Confusing?  We’re not done yet.

For the tone control, the volume doesn’t change, just the frequencies that get passed through the signal.  So for this use, a linear taper pot will provide a smooth sweep of the pot whereas an audio taper pot will have a fairly smooth sweep and then a big jump at around 60% – much like the linear taper pot when used for volume.  Ok, so you’ve got it all figured out now – audio taper pots for volume, linear taper pots for tone… easy right?  Well, that depends on how you use your volume and tone controls.  If you set your controls at 100% and never change them, then it really doesn’t matter which pots you use for volume and tone.  If you use your volume pot to control the gain of your amp and you want a lot of control over volume, then audio taper will be best.  If you like to do volume swells with your volume pot, then you may find it easier to do with a linear pot since the volume roll-off is much quicker and you wouldn’t need to rotate the volume knob as much to get that effect.  For the tone pot, if you rarely let the tone get dark but you like to take out some highs fairly often, you may find that an audio taper pot will make it easier to cut out higher frequencies without the sound becoming too dark too soon.

Hold on, what happened to that third option – the vintage taper?  Vintage taper pots have a sweep that sits right between audio taper and linear taper.  The “vintage” part comes from the fact that older pots had such inconsistencies in build quality that, to put it bluntly, they were all over the place.  So that not-quite-perfect sweep was designed into the vintage taper.  From my experience, vintage taper is much closer to audio than linear.  It’s just another option, and it’s good to have options.

So while the general rule that most guitarists start with is audio taper for volume and linear taper for tone, it’s a rule that can easily be broken depending your individual needs.

 

 

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