Whether you are a fan of effects loops or not, they can be useful tools. One of the go-to pedals in my collection isn’t an effect. It’s a standalone effects loop order switcher, which is basically a pair of dedicated effects loops (A and B) in an aluminum pedal enclosure. There are quite a few companies that make a version of this type of device. Some of these units have many other options included and some are very basic, with no knobs at all. I like to have a somewhat simple one hanging around, with an input, an output, and two sets of send/return jacks. Each channel needs a volume knob, a foot switch, and a bypass indicator light.
A loop switcher can be an especially useful tool when putting together a pedalboard, or even just adding a new stompbox to the mix. Signal paths can be auditioned to see how pedals will interact together before committing them to Velcro. I find it is also super fun and handy to use a switcher when doing sound explorations and, ultimately, in my writing and recording processes. There are so many more options sound-wise, depending on how effects are ordered. The rather simple unit I made allows for quick changes, which helps me economize my time. In fact, it’s so useful that I have one living full-time on my pedalboard, in a really accessible spot, so I can plug and unplug on the fly if something isn’t working out sound-wise.
Fancier loop-switching devices can have true bypass switching, buffers, lots of sends and returns, knobs, signal paths routed any which way.... The options are nearly endless. Plenty of pedal builders out there can build custom units for a reasonable price, tailored to anyone’s specific taste. You might even go the rackmounted, pro-audio hardware route if you want to get extra fancy!
There are several different commercial A/B loop switcher units available that are on the simpler end of the spectrum, like the JHS Switchback A/B Effects Loop Switcher ($102 street) and the MXR M196 A/B Box Pedal ($59 street). The EarthQuaker Devices Swiss Things Pedalboard Reconciler ($249 street) is an awesome utility pedal with a few more helpful options. My absolute favorite simple go-to is the Boss LS-2 Line Selector Pedal ($113 street). It’s got a small footprint and does all the basics. Plus, it’s Boss, so it’s built like a tank. Mine has survived 20 years of abuse so far.
Whether you are a fan of effects loops or not, they can be useful tools.
Some pedals sound totally different when inserted into an effects loop instead of being inserted directly in line. It’s really informative to be able to hear those differences. I feel like a whole new world opened up to me when I started using the LS-2. Some of my favorite sounds that I have been able to create came from putting pedals in the loop that normally get chained up in line directly. Give it a try! And for those who DIY, check out Beavis Audio Research’s awesome site. There are several different iterations to build.
Note the two trimmer screwdriver slots, surrounded by blue, in the middle of this phase shifter.
There is a type of potentiometer called a trimmer (also known as a trimpot) that lives inside of some stompboxes. It typically doesn’t have a shaft that sticks up like a regular potentiometer. Trimmers usually have a slot on top for making adjustments with a small screwdriver. They are meant to be set correctly when installed in a device, and mostly never seen or adjusted by the device’s user. Trimmers can be variable resistors, variable capacitors, or trimmable inductors, and they can perform many different types of functions within a circuit.
“I know what an epiphany it can be to unlock that little extra bit of magic out of an already beloved pedal.”
I get a fair amount of questions about trimmers—often: “Is it okay to mess with that?” There are many pedals on the market that have internal trimmers that can be adjusted by users, to tweak to personal taste. It is handy to be able to dial a sound in all the way, almost like fine-tuners on a guitar. Typical user-tweakable micro controls are for modulation speed and/or width, gain, and sensitivity.
Conversely, there are trimmers built into circuits that I would not consider easily user-adjustable. These include things like bias for time-based effects and setting proper voltages so circuits can function as they should. I’ve repaired quite a few analog delays and flangers, for example, that were perfectly functional! The bias had simply drifted out of its sweet spot. Perhaps the user had gotten too curious and decided to tweak those irresistible little trimmers? Or, more often than not, the trimmers had simply drifted a bit away from their set positions over many years of use, not to mention jostling from being transported to and from gigs. A qualified pedal tech has the right meters and test equipment to get those effects dialed right back in. However, bias can be a nightmare to get back to where it needs to be without some expertise. I understand why these folks thought their pedals were broken. A modulation effect that isn’t properly biased can sound absolutely horrible!
Internal timmers, aka trim pots, come in a variety of shapes and sizes. Look for the slots.
It’s only natural to be curious about the guts inside pedals. Trimmers can add so much extra versatility to a device. If you’re ever unsure which ones are okay to tweak, a good rule of thumb is to ask the builder or the company that makes a particular unit which of its trimmers are okay to fiddle with before you twiddle. In some cases, your warranty could be voided if you do adjustments, so it’s always a good idea to check first.
I know from my own playing what an epiphany it can be to unlock that little extra bit of magic from an already beloved pedal, and I enjoy sharing any knowledge that can help guitarists get the sounds that are most pleasing out of their effects. Perhaps that pedal you planned to trade could be transformed into something you really love with a little twist of a trimmer.
A Deeper Dive
I mentioned resistors several times in this column. A resistor is a passive, 2-terminal electrical component that controls electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses.
- Does your favorite stomp have an adjustable trimmer? You can find a list of popular guitar pedals that have adjustable trimmers here.
- To read more about voltage dividers, and how a potentiometer works, check this article out.
- And here’s some great information about trimmers, for further exploration.
Fig. 1
Your pedal’s designer specifies every component value in a design to result in a particular timbre or function and needs to know how much each component employed might vary from that specified value. When manufacturers make parts, they specify the nominal value and a particular tolerance value. Often, this tolerance is specified as a percentage of the nominal value. So, a 10-percent tolerance in a 1k-ohm resistor could be anywhere from 900 ohms and 1100 ohms. The higher the tolerance figure, the more variation you can expect in the value of a given component.
Fig. 2
While more variation may seem like strictly bad news at first blush, it does have some benefits—principally, cost. The machines and processes required to make a one-percent resistor are cheaper and faster than those required to make a resistor of arbitrarily higher precision. Consequently, a run-of-the-mill one-percent tolerance resistor may cost five cents while its 0.005-percent laser-trimmed counterpart costs $12. If vintage pedal prices are starting to make you queasy, know that it could be much worse. Demand plays a major role in cost as well, as it is pretty rare that you need a 0.005-percent resistor.
So, what difference does tolerance make and how do we know when we need to splurge for the caviar components? Without getting too far into the mathematical weeds, here’s a couple examples. Take Fig. 1, where a very simple resistor/capacitor low-pass filter is shown. This filter’s corner frequency [Fig. 2] is determined by the value of the resistor and capacitor, and that frequency has a certain sensitivity to variations of those values. [Note: The corner frequency is also known as the cut-off frequency—frequencies above this point will be attenuated by the low-pass filter.] In this particular circuit, if we wiggle the capacitance value by 10 percent, the corner frequency will move by approximately 10 percent.
Fig. 3
The corner frequency of the inductor/capacitor low-pass filter in Fig. 3 has a different sensitivity to changes in the value of the capacitor. If we increase the value of the capacitor by 10 percent, the corner frequency of the filter moves by approximately five percent. So, we can say that the corner frequency of the Fig. 3 circuit is less sensitive to changes in the capacitance than the Fig. 1 circuit. If you want to build circuits that are more forgiving of changes in component values, you can make some design decisions that will help!
You can also quantify what difference component variation will make in the context of your particular application. Let’s assume we’re employing the circuit in Fig. 1 as a pedal power supply filter. Let’s set resistance at 470 ohms and capacitance at 220 µF. We know we’re primarily wanting to filter 60 Hz hum from our power line, and at this nominal value of R (resistance) and C (capacitance), we can attenuate 60 Hz by approximately 32 dB. If we choose a 20-percent capacitor, in the worst case, our C drops 20 percent to 176 µF and we only reduce that 60 Hz noise by 30 dB. In practice, that difference of 2 dB probably won’t result in a dramatic difference in performance. This tolerance to higher tolerance parts is one of the reasons why we see 20-percent capacitors in big power supplies. When bigger is better, some amount of overkill can make variations in value a non-issue, practically.
Whether you’re bending your own circuits or just trying to figure out why you can’t find a backup that’s quite as good as your No. 1 dirtbox, you might consider how the imperfections in those little devices inside our devices add up to make something special.
