Multimeter: how to use it with DIY guitar pedals

If you have already made guitar pedals, you know that my rule is "It NEVER works at the first attempt"!

This can be very frustrating sometimes, and even if debugging can work easily or if an audio probe can sometimes do the trick, you can end up stucked with a non working guitar pedal.

If you are in that case, it's time for the multimeter to come into play and to become your best friend!

What is a multimeter? Which one should I use?

The multimeter is a device that can measure different stuff (hence the name "multi" + "meter" 😃 )

It is an amazing tool for debugging guitar pedals or optimize them. It is also very helpful to understand how they work!

Most of the multimeters out there measure voltage, intensity, resistance (in Ω) and continuity. But some of them can even measure capacitance, transistors characteristics like hfe or temperature!

I think the following features are the best for building guitar pedals:

• Voltage
• Intensity
• Resistance
• Continuity (with noise)
• Transistor hfe (optional)

 Good news is: it is not even expensive! 

Personally, I use a Meterk TRMS 6000 that is a cheap multimeter that you can find on amazon. This is an equivalent multimeter. It has all the features that you need when building guitar pedals, is very simple to use, accurate enough and cheap. Perfect tool to start with!

Another cool thing with it is that you can put it like this on your bench (more useful than you think, it is not only for cool pictures!):

If you want a professional grade tool that you will keep and use for many years, a Fluke 15+ multimeter is a good pick. Fluke is THE reference in the industrial world, and they provide very robust and reliable tools. However, you will not get the hfe measurement functionality unfortunately, because the norm is quite hard for this kind of industrial multimeter. Fortunately, there are other quite cheap tools that you can use that I will present later in another article.

How to use a multimeter?

Using a multimeter is fairly easy. Here is a schematic of the multimeter

You can turn the central wheel to select what you want to measure. Then, put the black probe on the ground part of your circuit (an input jack is easy to use), and you can use the other probe to measure what you want.

You can also use an alligator clip to ground the black probe. It is easier to manipulate the other probe this way.

There are many uses for a multimeter with DIY guitar pedals. Let's check out what you can do with it.

Measuring voltage (of course!)

By setting the multimeter wheel on "V" position, you can measure voltage anywhere in a circuit. Just place the red probe on the spot you want to measure voltage and the black probe on ground.

(no power supply on the above picture... So no voltage obviously!)

It is very useful to check transistor bias, but also identify power supply issues!

Some circuits also provide "testing voltages" around the circuit: use your multimeter to verify that you have the correct voltages.

Finally, if you ever decide to work on amps, it’s a vital way to ensure your own safety by checking that there is no residual charge left in the power supply filter capacitors. (These capacitors can be lethal if not properly discharged!)

Finding false contacts

Short circuits and false contacts are a classic with DIY guitar pedals, especially if you use veroboard.

The continuity mode is very helpful fort that. Just place the two probe on each row of the veroboard and check if it bips or not! If you have contact, there is short somewhere!

 

It is a very useful feature if you have suspicion of a short somewhere in your circuit.

It is also very useful to check that everything that should be connected to ground IS connected to ground.

Caution! Continuity and resistance measurements do not work properly on a live circuit! Sometimes it can even fry the multimeter... 😭 Always take your continuity and resistance measurements with the power disconnected.

Measuring vintage components

Old components have the rather annoying habit of drifting in value with time or having crazy tolerances. This is especially true for electrolytic caps (that often need to be replaced anyway), film capacitors with 20% tolerances and carbon comp resistors.

Here is an example from my small stock of carbon resistors:

Orange - orange - orange = 33 x 10³ = 33kΩ in theory

Always check vintage components prior to using them if you want to avoid bad surprises.

Measuring transistor bias and hfe

If you want to make sure that the transistors of your circuit are correctly biases, you can easily measure the voltage at their collector, base and emitter with a multimeter.

Sometimes, voltage values are given for each pin of each transistor so you can quickly check if you have not make any mistake.

Also, it can help you select the best transistors for your build. Some circuits require matched transistors hfe for an optimal performance (octave circuits for instance, or fuzz). It is also nice to know what the gain of most common transistors is.

Here is a 2n5088 that is being measured for a build of mine:

460 is a medium gain, perfect for some builds like a Big Muff if you want to avoid introducing too much noise in your circuit but still having a good amount of gain. A classic 2n5089 has a gain more into the 600-800 territory for example.

To measure a transistor hfe, simply turn the wheel on the hfe position, then place the transistor in the socket between func and hold button. Pay attention to the nature of the transistor (npn or pnp) and its pinout (EBC...etc.). Some vintage transistors have weird pinout so check the datasheet before!

Careful: this measurement usually do not work with germanium transistors. They have a bad habit of having current leakage, which false hfe measurements. If you plan on building several circuits with germanium transistors (a sweet Fuzz Face with AC128s, for example 👍), you might want to invest in a small specialized tester that accurately measures hfe accounting for leakage current.

Measuring the current draw of a pedal

If you want to know how much mA your DIY guitar pedal consume,the multimeter can also do it!

Just put it in series between your battery clip + wire (or the +9V pin of the power supply jack) and the voltage input of your circuit. 

To make things easier, you can use this thing:

For our guitar pedals, consumption is generally very reasonable so you can keep the probe on the mA jack.


Of course, a multimeter has a lot of other possible usages: testing pickups outputs, checking the wiring...etc. Try to experiment with it as well to learn how it can be useful to you!


There it is!
I hope this article was useful to you! If you liked it, thank me by liking the Coda Effects Facebook page or follow Coda Effects on Instagram.