Discover the sound-sculpting properties of bright caps and how to tame treble acoustically.
I enjoy clarity and chime, so I really like the open-top-end sound of a bright cap across the volume pot. Some folks do not and remove them, finding mellow mojo. What follows is an explanation of what bright caps are and how they work, plus general treble tips to consider on our journey from kilocycles to kilohertz.
When a guitar signal travels through an amp and encounters a large resistance, the high frequencies tend to sound more attenuated or shelved compared to the lower frequencies. Bright caps exist to restore this perceived loss of openness and treble. The features on most analog amps work by subtraction—throwing signal away (series resistance) to create an aural effect. Passive tone controls, reverb circuits, and volume controls are prime examples. Almost every classic guitar amp has a bright cap on the volume control. A volume potentiometer will typically be a 1-megaohm resistor with a variable tap/wiper. The top of the pot (the resistor) is connected to the signal source and the bottom is connected to ground (zero signal). The wiper sweeps between the two ends and is our variable output level—controlling the volume range, from silent to loud.
Vive la résistance! Let’s consider a loud-ish at-home playing level, with the volume set to 3. I’m visualizing a classic blackface Fender volume knob here. How does this setting translate into series resistance? It’s around 850,000 ohms! That’s 850k ohms in series to the wiper (output) and 150k ohms to ground: 1-megaohm total (Image 1). The snappy guitar signal enters the 850k resistance but sounds dull and flat once it passes through. How do we fix that? That’s where a bright cap comes in. A small-value capacitor—usually in the 47-to-250 pico farad (pF) range—is connected from the pot’s maximum signal point to the wiper output. Now the highs jump over the 850k resistance through the bright cap to the wiper and out to the next stage, creating sonic balance. In this example, a typical blackface signal passing through a 100 pF bright cap allows highs in the 2,000 Hz range and more to pass the resistor more easily. So, our guitar’s “air” and glassy leading edge is restored!
If you want more of a good thing, increase the bright cap’s value and the fast-lane frequency drops lower, allowing more and more upper-mid bite along with the shimmer. Or reduce the bright cap value for a rounder, softer sound. Often just a little is enough for clean tones. High-gain and classic British amps have big bright cap values of 500 pF up to 5000 pF (or .005 µF). Large bright caps like that over a 1-megaohm pot really push upper mids and give you searing overdrive. Such big cap values are generally not good for clean tones and can sound “honky” when you turn the volume down.
Many favored amps have bright caps. Fender Twins and Super Reverbs have a 10 pF bright cap over a 3.3-megaohm series signal resistor. In many Marshall amps there is a 500 pF bright cap over the 470k resistor leading to the second gain stage.
So how can we use this info? If you have an amp you feel is too edgy or bright for your taste, you can remove or change the value on one of these caps and see if you like the sound better. Volume pot bright caps are easy to experiment with. Try smaller values than stock for a more subtle lift in the top or go larger for more aggressive tones. You can also add a series resistor in line with your bright cap. This will pad down the bright cap’s effect and soften the leading edge. Note: If you don’t know how to discharge caps, then a tech is the way to go for safety’s sake. Bright cap mods are straightforward, so they should be affordable.
More treble tips. But before trying any internal mods, experiment with room position and treatment. You probably know this, but it’s worth repeating: single-coil pickups are brighter than humbuckers, bridge position pickups are brighter than neck position, pickups raised closer to the strings are brighter, rooms with exposed hard surfaces (glass, uncovered hardwood floors, sheet rock, or brick walls) are brighter than rooms with rugs and soft furnishings. Amps sitting on the floor positioned near walls or corners sound fuller and darker compared to amps away from walls, and amps on raised platforms (stands or chairs) or tilted up are brighter. If your amp sounds too bright, try placing a small rug under and in front of it while keeping the amp close to a wall. This can do a surprising amount of tone shaping, and it’s easier than digging into the circuitry. In a live band setting, put your amp up on a chair and think of it as your personal monitor. Lifting it off the ground will help your sound cut through and stay tight, plus it puts the speaker closer to your ear level. One more thing: Mid controls contain a lot of treble, too, so experiment with lowering mids to reduce treble.
WARNING:All tube amplifiers contain lethal voltages. The most dangerous voltages are stored in electrolytic capacitors, even after the amp has been unplugged from the wall. Before you touch anything inside the amp chassis, it’s imperative that these capacitors are discharged. If you are unsure of this procedure, consult your local amp tech.
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Created in collaboration with legendary guitarist George Lynch of Dokken and Lynch Mob fame, the Mr.Scary Mod adds an adjustable tube gain stage and an onboard Deep control, which together are designed to enable an amp to have increased sustain while still retaining note definition and dynamics.
LegendaryTones, LLC today announced production availability of its new Mr. Scary Mod, a 100% pure tube module designed to instantly and easily expand the capabilities of many classic amplifiers with additional gain and tone shaping. Created in collaboration with legendary guitarist George Lynch of Dokken and Lynch Mob fame, the Mr.Scary Mod adds an adjustable tube gain stage and an onboard Deep control, which together are designed to enable an amp to have increased sustain while still retaining note definition and dynamics.
Originally released as the Lynch Mod in February 2021, the updated Mr. Scary Mod features the same core circuit as the Lynch Mod but is now equipped with a revised tube mix combo per George’s preference as well as a facelift in a newly redesigned electro-galvanized steel enclosure. As with the Lynch Mod, each run will be limited and the first run in Pumpkin Orange with Black hardware is limited to just 150 pieces worldwide.
The Mr. Scary Mod adds an adjustable tube gain stage on top of the cathode follower position, keeping note definition and articulation while further increasing sustain. Each Mr. Scary mod is meticulously built by hand in the USA, one at a time, and tuned using high-grade components. Equipped with a single ECC81 (12AT7) in the first position and ECC83 (12AX7) in the second, the Mr. Scary Mod can clean up beautifully when rolling down your guitar’s volume, and still adds scorching gain when you roll it back up. This is a gain stage that’s been tuned and approved by the ears of the maestro George Lynch himself.
“The Mr. Scary Mod excels with dynamics and is incredibly touch-responsive, allowing me to shift from playing clear, lightly compressed cleans to full-out aggressive sustain and distortion –and control it all simply by varying my guitar’s volume control and picking,” said GeorgeLynch. “In many ways, it’s an old-school approach, but it’s also so much more natural and expressive in addition to being musically fulfilling when you can play both the guitar and amp dynamically together this way.”
The Mr. Scary Mod installs in minutes, is safe and effective to use, and requires no special tools or re-biasing of the amplifier. Simply insert the module into the cathode follower preamp position of compatible amplifiers (includes Marshall 2203/2204/1959/1987 circuits) and
immediately get the benefit of enjoying a hot-rodded amp that delivers all the pure harmonic character that comes with an added pure tube gain stage. The handmade in the USA Mr. Scary Mod is now available to order for $319.
For more information, please visit legendarytones.com.
October Audio has miniaturized their NVMBR Gain pedal to create two mini versions of this beautifully organic-sounding circuit – including an always-on gain device.
The NVMBR Gain is a nonlinear amp that transitions gracefully from clean boost to overdriven tones. Volume increases from just over unity to about 10db before soft-clipping drive appears for another 5db of boost. Its extraordinary ease of use is matched by outstanding versatility: you can use it as a clean boost, push a stubborn amp into overdrive or create a just-breaking-up sound at any amp volume.
October Audio’s new family of mini NVMBR Gain pedals includes a switchable version that allows you to bypass the effect: one option features brand logo pedal graphics, while the other sports a fun “Witch Finger” graphic with a Davies knob as the“fingernail”.
The second version in the new lineup is an always-on device featuring the Witch Finger graphic and Davies knob, with the same NVMBR Gain circuit that lies at the core of the switchable version.
- Knob controls gain and clipping simultaneously
- Stunning silver hammertone finish
- Switchable versions are true-bypass, available with classic or witch finger graphics
- Authentic Davies knobs, including the “fingernail”
- 9V center negative power supply required
- Dimensions: 3.63 x 1.50 x 1.88 in
Witch Finger (always on NVMBR Gain) demo
All October Audio pedals are assembled in Richmond, VA, and available for purchase directly through the online shop. Street price is $109 for NVMBR Gain footswitch versions and $89 for the always-on device.
For more information, please visit octoberaudio.com.