Note the two trimmer screwdriver slots, surrounded by blue, in the middle of this phase shifter.
Potentiometers are used for most of the controls on pedals and a lot of other electronic equipment as well. A potentiometer (also known as a pot) is defined as a 3-terminal variable resistor in which the resistance is manually varied to control the flow of electrical current. A potentiometer acts as an adjustable voltage divider. Any control on a guitar pedal that has a knob will typically be controlling a potentiometer, or sometimes a rotary switch.
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.
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Sterling Vermin RAT
The Sterling Vermin was born from a desire for something different — something refined, with the soul of a traditional RAT pedal, but with a voice all its own.
Built in small batches and hand-soldered in ACT’s Jackson, Missouri headquarters, the Sterling Vermin is a work of pure beauty that honors the brand legacy while taking a bold step forward for creativity.
The Sterling Vermin features the LM741 Op-Amp and a pair of selectable clipping diodes. Players can toggle between the traditional RAT silicon diode configuration for a punchy, mid-range bite, or the BAT41 option for a smoother, more balanced response. The result is a pedal that’s equally at home delivering snarling distortion or articulate, low-gain overdrive, with a wide, usable tonal range throughout the entire gain spectrum.
The pedal also features CTS pots and oversized knobs for even, responsive control that affords a satisfying smoothness to the rotation, with just the right amount of tension. Additionally, the polished stainless-steel enclosure with laser-annealed graphics showcases the merging of the pedal’s vintage flavor and striking design.
From low-gain tones reminiscent of a Klon or Bluesbreaker, to high-gain settings that flirt with Big Muff territory — yet stay tight and controlled — the Sterling Vermin is a masterclass in dynamic distortion. With premium components, deliberate design and a focus on feel, the Sterling Vermin is more than a pedal, it’s a new chapter for RAT.
Last August, metalcore giants Poison the Well gave the world a gift: They announced they were working on their first studio album in 15 years. They unleashed the first taste, single “Trembling Level,” back in January, and set off on a spring North American tour during which they played their debut record, The Opposite of December… A Season of Separation, in full every night.
PG’s Perry Bean caught up with guitarists Ryan Primack and Vadim Taver, and bassist Noah Harmon, ahead of the band’s show at Nashville’s Brooklyn Bowl for this new Rig Rundown.
Brought to you by D’Addario.Not-So-Quiet As a Mouse
Primack started his playing career on Telecasters, then switched to Les Pauls, but when his prized LPs were stolen, he jumped back to Teles, and now owns nine of them.
His No. 1 is this white one (left). Seymour Duncan made him a JB Model pickup in a single-coil size for the bridge position, while the neck is a Seymour Duncan Quarter Pound Staggered. He ripped out all the electronics, added a Gibson-style toggle switch, flipped the control plate orientation thanks to an obsession with Danny Gatton, and included just one steel knob to control tone. Primack also installed string trees with foam to control extra noise.
This one has Ernie Ball Papa Het’s Hardwired strings, .011–.050.
Here, Kitty, Kitty
Primack runs both a PRS Archon and a Bad Cat Lynx at the same time, covering both 6L6 and EL34 territories. The Lynx goes into a Friedman 4x12 cab that’s been rebadged in honor of its nickname, “Donkey,” while the Archon, which is like a “refined 5150,” runs through an Orange 4x12.
Ryan Primack’s Pedalboard
Primack’s board sports a Saturnworks True Bypass Multi Looper, plus two Saturnworks boost pedals. The rest includes a Boss TU-3w, DOD Bifet Boost 410, Caroline Electronics Hawaiian Pizza, Fortin ZUUL +, MXR Phase 100, JHS Series 3 Tremolo, Boss DM-2w, DOD Rubberneck, MXR Carbon Copy Deluxe, Walrus Slo, and SolidGoldFX Surf Rider III.
Taver’s Teles
Vadim Taver’s go-to is this cherryburst Fender Telecaster, which he scored in the early 2000s and has been upgraded to Seymour Duncan pickups on Primack’s recommendation. His white Balaguer T-style has been treated to the same upgrade. The Balaguer is tuned to drop C, and the Fender stays in D standard. Both have D’Addario strings, with a slightly heavier gauge on the Balaguer.
Dual-Channel Chugger
Taver loves his 2-channel Orange Rockerverb 100s, one of which lives in a case made right in Nashville.
Vadim Taver’s Pedalboard
Taver’s board includes an MXR Joshua, MXR Carbon Copy Deluxe, Empress Tremolo, Walrus ARP-87, Old Blood Noise Endeavors Reflector, MXR Phase 90, Boss CE-2w, and Sonic Research Turbo Tuner ST-200, all powered by a Voodoo Lab Pedal Power 2 Plus.
Big Duff
Harmon’s favorite these days is this Fender Duff McKagan Deluxe Precision Bass, which he’s outfitted with a Leo Quan Badass bridge. His backup is a Mexico-made Fender Classic Series ’70s Jazz Bass. This one also sports Primack-picked pickups.
Rental Rockers
Harmon rented this Orange AD200B MK III head, which runs through a 1x15 cab on top and a 4x10 on the bottom.
Noah Harmon’s Pedalboard
Harmon’s board carries a Boss TU-2, Boss ODB-3, MXR Dyna Comp, Darkglass Electronics Vintage Ultra, and a Voodoo Lab Pedal Power 2 Plus. His signal from the Vintage Ultra runs right to the front-of-house, and Harmon estimates that that signal accounts for about half of what people hear on any given night.
