One of the basic skills that a guitar player should acquire is the ability to detect what is wrong with his instrument. Simply knowing how to test guitar pots with a multimeter, won’t hurt and will save you a lot of trips to that guitar repair shop across town.
We will tackle today the importance of potentiometers and how their present condition can be determined using a multimeter, which is one of the most versatile devices out there.
Testing the electronic parts of your guitar is a non-destructive activity that doesn’t require you to desolder nodes, cut wires or remove entire circuits. Our only objective in testing is getting information that can help us avoid or solve problems that may arise from faulty potentiometers.
With the help of a multimeter, we can find issues that may be preventing your instrument from performing to its full potential. This way you will know what to do next to address the existing drawback.
Before proceeding with this exercise, be reminded that whether it is related to wood or electronics, safety should always be your number one priority when engaging in any sort of guitar work.
What are guitar potentiometers?
On the surface, a guitar looks like a simple machine, but in reality it is a complex network of parts with their own specific roles to fulfill. An example of an often overlooked guitar part is the potentiometer, which despite its diminutive nature, has provided guitarists the power to shape tone in a myriad of ways.
Potentiometers, or pots, are three-terminal resistors that can also act as a variable resistor if only two terminals are used. Through the use of its sliding or rotating contact, it can create an adjustable voltage divider. Located underneath the knobs of your guitar and your amplifier, potentiometers that affect your instrument’s tone and volume, granting you full control of your tonal palette.
Electric guitars with passive pickups usually come equipped with pots within the 250K ohm, 300K ohm, 500K ohm resistance ranges. On the other hand, active pickups usually use 25K ohm pots.
What is a multimeter?
A multimeter is a handheld tester commonly used by electricians to troubleshoot electrical problems on various machines and devices. One of the mainstays in a DIY toolbox, multimeters can measure electrical current, resistance and voltage, as well as other values.
Multimeters are not only for testing guitar pots, they can also be used on appliances, circuits, power supplies and other guitar parts such as pickups and input jacks. They also come in analog and digital versions.
Analog Multimeters
Utilizing a needle that kicks over a graduated scale whenever it detects electrical current, analog multimeters aren’t going to be entirely replaced by its digital counterpart soon. Despite a few disadvantages of analog testers, such as its less user-friendly features, it has remained fairly popular for its lower price and user base familiarity.
Digital Multimeters
In place of a needle is an LCD screen that conveniently displays a more accurate readout compared to analog. Even though digital multimeters cost more, they are still more preferred for their improved voltmeter function and higher resistance. Digital multimeters are also easier to come by and are always available in most electronics shops and home improvement stores.
How to use a multimeter
Analog and digital testers share the same basic functions and mode of operation. These devices come with a red and a black lead used for probing. The black goes into the “common” port, and the red one goes into the port that corresponds to your purpose.
After the leads have been plugged in place, you may select the function and range according to whatever you will be testing. You will then use the lead to touch a terminal or a tip of a wire to either check connectivity and compatibility problems on specific parts.
When testing for guitar pots, you may also opt for a test probe that comes with an alligator clip instead of a lead. This way you can free your hand to handle other things such as changing settings and testing the other nodes or pins.
These devices are fairly safe to work with on energized circuits as long as the current or voltage stays below the tester’s maximum rating. When using testers on energized equipment, never touch the metal tips of the leads to avoid electrical shock.
Testing guitar pots with a multimeter
Resistance reading
Plug the black lead into the “common” port and the red lead to the voltage/ohms port. Then using the dial, choose a setting that’s higher than the resistance of your pots. You may choose 2,000 ohms if the resistance is not indicated at the bottom of the pots.
Now let the black lead touch the first pin from the left and let it stay there while you use the red lead to touch the third pin on the right. It will instantly display the resistance reading on the screen if you are using a digital tester (if it displays 491, that means it is a 500k ohm potentiometer).
Assuming you conducted the test correctly but registered no reading at all, that means you have a bad potentiometer that needs to be replaced.
Audio (logarithmic) vs linear pots test
To determine if your pots are audio or linear, turn the knob all the way down to zero. Place the black lead on the left-most pin and the red lead on the middle pin (also known as the “wiper”).
Turn the knob halfway and if the displayed resistance turns up 50% then it is a linear pot. For audio pots, most of the boost will only come towards the end of the knob’s turn.
Take note that there is no such thing as right and wrong when choosing between audio and linear potentiometers, it all boils down to personal preference.
In-circuit testing
You may also test pots in circuit, meaning you won’t have to de-solder and take them off the circuit board. Just open the back cavity of your guitar and test the guitar pots with your multimeter. This time you are accessing the pots from the bottom, so mind the proper placement of the tester probes.
