After searching for some info on replacement pickups for my Epiphone Les Paul Standard, I got sucked into the black hole that is the world of guitar wiring a few weeks ago. There seems to be a lot of opinions on various options: linear or audio taper pots? 50’s or modern tone control wiring? .022uF or .047uF caps, etc. etc. But there was very little data to support any position, or to help someone understand exactly what these various changes do.
In searching for a way to actually determine the effects of these various options, I stumbled upon LTspice circuit simulation software (free download: http://www.linear.com/designtools/software/) and with the help of a few different online resources, I was able to build a simple simulated guitar wiring circuit – consisting of a single pickup, volume control, and tone control with which I could test various changes.
First up was linear taper pots vs. audio taper pots for volume control. Many people were saying to use audio taper pots for volume control, since your ears hear changes in sound ‘logarithmically’, which is why we use the logarithmic decibel scale to express sound level, rather than a linear scale. That seemed to make sense; but then why did my Epi come with linear volume pots, and most (all?) Gibson’s as well (http://www.gibson.com/service/tech/schematics/)?
Here’s the LTspice circuit I used for simulation:
This is basically half of a Les Paul with stock wiring: one pickup (constructed of a voltage generator which sweeps from 20Hz to 10kHz, and which has some resistance, capacitance, and inductance), a 500k volume pot, a 500k tone pot, .022uF tone cap, plugged into an amp with an 800k input impedence.
At this point I’ll mention that while I’m a nerd (obviously), I’m not an electrical nerd, so while I’ve done my best to make a relatively accurate model, if anyone with more electrical experience wants to critique the circuit, or any of the values I’m using, feel free. Even if it’s not perfect though, I think it will still demonstrate the trends that various changes make, just don’t pay too much attention to the exact numbers (they’d change based on your pickups, amp, etc. anyway).
So, here’s what you get when you adjust a linear taper volume pot in this circuit:
This chart shows frequency response lines for 10, 8, 6, 4, and 2 on the volume knob (0k, 100k, 200k, 300k, 400k resistance). 500k is not shown since that’s when the signal from the pickup is going straight to ground, so the output would be zero.
And here’s the output for when you use the same 10, 8, 6, 4, and 2 setting on the volume knob, but with a 10% audio taper pot (Bourns PDB183-GTR audio taper)
Notice that the linear taper pot gives pretty much equal 3 dB steps when adjusting from the volume know from 10 down to 4, with the step from 4 to 2 being closer to 6 dB.
On the other hand, the audio taper pot only drops about 0.75 dB for the first couple steps, and then the output starts to drop exponentially from there.
From these results, it seems like the linear taper pots are actually the ones that adjust the volume level closer to the same ‘logarithmic way’ that we hear (since the charts are showing decibel levels). The audio taper pots are barely going to reduce the perceived volume level at all during the first half of the pots rotation, and then drop off very quickly from there.
Given these results, and given the fact that I’ve been happy with my current linear taper pots, I’m planning on sticking with a linear taper for my volume pots.
Anyone else find this informative? Anyone want analyses of other wiring changes (50’s wiring, treble bleed, etc.)?
In searching for a way to actually determine the effects of these various options, I stumbled upon LTspice circuit simulation software (free download: http://www.linear.com/designtools/software/) and with the help of a few different online resources, I was able to build a simple simulated guitar wiring circuit – consisting of a single pickup, volume control, and tone control with which I could test various changes.
First up was linear taper pots vs. audio taper pots for volume control. Many people were saying to use audio taper pots for volume control, since your ears hear changes in sound ‘logarithmically’, which is why we use the logarithmic decibel scale to express sound level, rather than a linear scale. That seemed to make sense; but then why did my Epi come with linear volume pots, and most (all?) Gibson’s as well (http://www.gibson.com/service/tech/schematics/)?
Here’s the LTspice circuit I used for simulation:
This is basically half of a Les Paul with stock wiring: one pickup (constructed of a voltage generator which sweeps from 20Hz to 10kHz, and which has some resistance, capacitance, and inductance), a 500k volume pot, a 500k tone pot, .022uF tone cap, plugged into an amp with an 800k input impedence.
At this point I’ll mention that while I’m a nerd (obviously), I’m not an electrical nerd, so while I’ve done my best to make a relatively accurate model, if anyone with more electrical experience wants to critique the circuit, or any of the values I’m using, feel free. Even if it’s not perfect though, I think it will still demonstrate the trends that various changes make, just don’t pay too much attention to the exact numbers (they’d change based on your pickups, amp, etc. anyway).
So, here’s what you get when you adjust a linear taper volume pot in this circuit:
This chart shows frequency response lines for 10, 8, 6, 4, and 2 on the volume knob (0k, 100k, 200k, 300k, 400k resistance). 500k is not shown since that’s when the signal from the pickup is going straight to ground, so the output would be zero.
And here’s the output for when you use the same 10, 8, 6, 4, and 2 setting on the volume knob, but with a 10% audio taper pot (Bourns PDB183-GTR audio taper)
Notice that the linear taper pot gives pretty much equal 3 dB steps when adjusting from the volume know from 10 down to 4, with the step from 4 to 2 being closer to 6 dB.
On the other hand, the audio taper pot only drops about 0.75 dB for the first couple steps, and then the output starts to drop exponentially from there.
From these results, it seems like the linear taper pots are actually the ones that adjust the volume level closer to the same ‘logarithmic way’ that we hear (since the charts are showing decibel levels). The audio taper pots are barely going to reduce the perceived volume level at all during the first half of the pots rotation, and then drop off very quickly from there.
Given these results, and given the fact that I’ve been happy with my current linear taper pots, I’m planning on sticking with a linear taper for my volume pots.
Anyone else find this informative? Anyone want analyses of other wiring changes (50’s wiring, treble bleed, etc.)?
