The Keeley Filaments High Gain Distortion is a distortion pedal built for players who want metal levels of gain in a stompbox. Delicious Audio described it as Keeley Engineering's most earth-shattering pedal, "a high gain distortion created with metal-heads in mind"1. Where most overdrives are about pushing an amp gently, the Filaments emulates high-gain tube amps, with what Pedal of the Day called "an abundance of opportunities to yield crushing, ear-exploding tones"2.
The pedal was designed with a midrange carved out for metal. On That Pedal Show in 2017, Robert Keeley explained the intent: "I think we spend a lot of time carving out the mids to an area that was fun for my ears"3. Delicious Audio's write-up lists the metal styles the pedal's tone shaping is meant to cover, from Christian, Death, Black, Folk, Core, Grind, Crust Punk, Glam, Progressive Jazz and Stoner Metal1.
How the circuit works
The Filaments is built around three cascaded gain stages, with tone shaping placed between them, and a final stage that simulates a power tube section. Robert Keeley described it on That Pedal Show: "there's three cascaded gain stages so you get this overwhelming amount of gain then we shape it then with the tone contr..."3. Pedal of the Day counted the result as "3 layered stages of gain and 7 different ways to EQ you tone"2, and Delicious Audio called the seven-layer tone shaping the most flexible of any Keeley stompbox1.
Controls
Guitar Pedal X lists the full control set as Level, Presence, Gain, Bass, Body, Treble, plus Boost, Bright and Crunch switches4. Level and Gain set the stage for what Delicious Audio calls "rich layers of high gain tube-amp saturation"1, with Pedal of the Day noting both have "a fat spectrum to play with and delve into"2.
| Control | What it does |
|---|---|
| Level | Output volume, with a wide range2 |
| Gain | Sets the amount of high-gain tube-amp saturation1 |
| Bass | Adjusts low end frequencies2 |
| Body | Fine-tunes more lows, fat and beefy but not muddied2 |
| Treble | Added range of highs "to make your amp sing"1 |
| Presence | Works with the Bright switch to boost any pickup configuration2 |
| Boost switch | One of two levels of gain and compression12 |
| Crunch switch | The second of the two gain and compression voices12 |
| Bright switch | Works with Presence to give any guitar or pickup combination "the authority to stand up and shout"1 |
The Boost and Crunch switches are the pedal's voice selectors. Delicious Audio describes them as giving "two different levels of gain and compression to get your edge just right" for amps that are hard to push1. On the low end, Bass and Body together are credited with giving "the punch and authority of a gain monster no matter what size amp you are playing," with Delicious Audio noting the low-end bass response holds up even with a 10-inch speaker1.
Powering it
The Filaments can be run at 18V for more headroom and louder output, as Pedal of the Day pointed out2. That extra voltage is worth knowing about if you want more clean volume before the gain stages saturate.
What reviewers said
The pedal picked up press recognition early. On That Pedal Show, Robert Keeley noted it earned an award from Guitar Player magazine, Keeley's first since the compressor, along with a Guitar World Top Gear award3.
"One of my all-time favourite Keeley pedals, really versatile overall, with a slightly darker and denser profile at its c..."
Karlsson's 2025 roundup of compact high-gain and metal pedals called the Filaments a proper High Gain Chameleon that also does HM-2 style tones, meaning it can reach the Swedish death metal territory of the Boss HM-2 as well as its own voiced high-gain sounds4.
On That Pedal Show, Dan Steinhardt, Mick Taylor and Robert Keeley discussed the design intent and the circuit in a full segment on the pedal3:
Delicious Audio's page also carries a demo by Living Room Gear, played through a Fano PX6 guitar and a Tone King 20th Anniversary Imperial amp1.
Videos
ProGuitarShopDemos
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Keeley Electronics
Questions
Can the Keeley Filaments run at 18V?
Yes. Pedal of the Day notes that the Filaments can be run at 18V for more headroom and louder output. The higher-voltage option is there for players who want extra clean volume before the gain stages saturate.
Can the Keeley Filaments do HM-2 style tones?
Yes. Guitar Pedal X's Stefan Karlsson called it a proper High Gain Chameleon that also does HM-2 style tones, and named it one of his all-time favourite Keeley pedals, with a slightly darker and denser profile at its core.
What does the Boost switch on the Keeley Filaments do?
The Boost toggle gives you one of two different levels of gain and compression. Delicious Audio describes the Boost and Crunch switches together as offering two levels of gain and compression to get your edge right for amps that are hard to push.
What does the Body knob do on the Filaments?
The Body knob fine-tunes the low end, giving a fat and beefy sound without turning muddy. Delicious Audio pairs it with the Bass control as the source of the pedal's punch and authority, even through a small amp with a 10-inch speaker.
Sources (4)
- Keeley Filaments High Gain Distortion, Delicious Audio, 2018-03-21
- Keeley Electronics Filaments High Gain Distortion, Pedal of the Day, 2018-01-26
- That Pedal Show, That Pedal Show (YouTube), 2017-10-19
- Guitar Pedal X, Guitar Pedal X, 2025-11-27
