The Keeley HYDRA Stereo Reverb & Tremolo is a compact pedal that combines high-fidelity stereo reverb and tremolo in one box, designed and manufactured in Edmond, Oklahoma by Keeley Electronics1. It launched on November 17, 2020 at $249 USD1, and Guitar World reported it as available now at that price on launch day2. Delicious Audio describes it as the only tremolo plus reverb pedal in a compact format with a stereo output1.
Reverb and tremolo modes
The Hydra offers three reverb modes and three tremolo modes, and each effect runs in stereo1.
Guitar World described the reverbs as three high-fidelity stereo effects2, and Delicious Audio calls them "Dreamy and accurate sounding Spring, Plate, and Room Reverbs" paired with "Vintage-voiced Harmonic, Vibrato, and Sine Tremolo"1. Pedal of the Day framed the pedal's job simply: "Bathe your sound in Spring, Plate or Room Reverb" and "add tap-tempo enabled Harmonic, Vibrato, or Sine Wave Tremolo with the press of a button"3.
The tremolo modes cover the classic shapes. Harmonic tremolo splits the signal and modulates bass and treble against each other, Vibrato is really a pitch-wobble effect, and Sine Wave is the even, old-school amplitude pulse. With tap tempo on all three, you can lock the pulse to the tempo of a song rather than dialing it in by ear31.
Controls, presets and effect order
Each effect has its own separate footswitch, so you can run reverb alone, tremolo alone, or both together1. The knobs are dual-function, with tremolo functions labeled in black and reverb functions in white, and the second layer is reached by holding the Color knob1.
Pedal of the Day highlighted the Alt Controls as the pedal's smartest feature3:
"You can easily change the order of effects or the character of the Tremolo or Reverb with the HYDRA's smart Alt Controls"3
Pedal of the Day, February 20213
That means tremolo into reverb or reverb into tremolo, whichever suits the part. The pedal also stores up to three presets, which Pedal of the Day described as easy to save: "Save up to three presets with ease using our intuitive save feature"3.
Power and connections
The Hydra runs on 9V DC at 115mA, which Delicious Audio calls an ultra low-current design1. That draw is modest enough that it should sit comfortably on most isolated power supplies.
Connections are where the pedal earns its stereo billing:
- Stereo input and output, shared with the Eccos delay1
- TRS expression pedal input for real-time control1
- External tap-tempo input, for on-board or remote tap tempo1
- Works with guitar, bass, or keyboard signal3
- Can be used with pro remote switching systems3
Bypass is switchable between true bypass and trails on the fly, so reverb tails can be left to fade naturally when you disengage the pedal1. Guitar World's launch coverage also listed true-bypass switching among the features2.
Versions and notable players
Beyond the standard edition, the Hydra appeared in a few other forms:
- An Artist Series version with Ariel Posen's signature, unveiled in August 20211
- A custom edition featuring Headway artwork, seen in Premier Guitar's 2023 rig rundown of Ariel Posen4
Premier Guitar's reviewer, writing in 2024, called the Hydra "Keeley's excellent U.S.-made Hydra Stereo Tremolo and Reverb" and noted it was less expensive than the Flint, its obvious stereo tremolo-and-reverb rival5.
What reviewers said
Reviewers found the pedal approachable despite its flexibility. Pedal of the Day wrote that "although it is extremely user-friendly," and summed it up as "A complete end-of-pedalboard solution that fits perfectly in any musician's rig, regardless of genre"3.
Gearnews took a subtler read on its character:
"overall I get the impression its strength is in its subtleties, which can reward you with some lush, understated tones"6
Jef, gearnews.com, November 20206
MusicRadar's launch coverage gave the price as $249 / £2497, matching the $249 USD figure from Delicious Audio1 and Guitar World2.
Videos
Pete Thorn
Keeley Electronics
Keeley Electronics
Questions
Can you change the effect order on the Keeley Hydra?
Yes. The Hydra's Alt Controls let you change the order of the reverb and tremolo, so you can run tremolo into reverb or reverb into tremolo. The Alt Controls also change the character of the tremolo or reverb itself, and each effect has its own separate footswitch.
Does the Keeley Hydra have tap tempo?
Yes. The tremolo is tap-tempo enabled, and the pedal offers both on-board and remote tap tempo. There is an external tap-tempo input on the side, alongside a TRS expression pedal input, so you can sync the pulse from anywhere on your board.
Is the Hydra true bypass or trails?
Both, and you can switch between them on the fly. The Hydra ships with true-bypass switching, and reverb trails can be engaged while you play, so a bypassed note can still fade out naturally instead of cutting off abruptly.
How many presets does the Keeley Hydra store?
Up to three. Keeley describes the save feature as intuitive, so you can keep three reverb and tremolo combinations ready to recall, which is handy if you move between songs or sections that need different amounts of space and motion.
Does the Hydra work with an expression pedal?
Yes. The Hydra has a TRS expression pedal input, so you can sweep parameters in real time with a standard expression pedal. The same side of the pedal also carries an external tap-tempo input for remote control of the tremolo speed.
Is the Keeley Hydra the same as the Eccos?
No. The Eccos is Keeley's stereo delay, while the Hydra handles reverb and tremolo. The Hydra was designed as a companion to the Eccos, sharing the same controls and input and output configuration, so the two pedals sit together as a matched pair on a stereo board.
Sources (7)
- Keeley Hydra Stereo Reverb & Tremolo, Delicious Audio, 2025-10-07
- Keeley promises "a complete end-of-pedalboard solution" with the HYDRA Stereo Reverb & Tremolo pedal, Guitar World, 2020-11-17
- Keeley Electronics HYDRA Stereo Reverb & Tremolo, Pedal of the Day, 2021-02-24
- Slide Guitarist Ariel Posen Guitar Rig Rundown, Premier Guitar, 2023-01-11
- Keeley Zoma Tremolo and Reverb Review, Premier Guitar, 2024-11-13
- The new Keeley Hydra Stereo Reverb & Tremolo pedal, gearnews.com, 2020-11-17
- Unleash pulsating stereo ambience with the new Keeley HYDRA reverb and tremolo pedal, MusicRadar, 2020-11-18
