The Keeley Hydra is a stereo reverb and tremolo pedal from Keeley Electronics, the Oklahoma effects specialist, designed and manufactured in Edmond, USA12. Announced on 17 November 2020 and available at dealers worldwide the same day for $249, it combines high-fidelity reverb and tremolo in one compact box, with two footswitches so each effect can be switched independently324. Delicious Audio described it at launch as the only tremolo plus reverb pedal in a compact format with a stereo output3.
The idea is simple: bathe your sound in reverb, then add tremolo on top, or use either effect on its own. The pedal works for guitar, bass or keyboard signals, and Pedal of the Day found it "combines high-fidelity Reverb and Tremolo to add space and dimension" while remaining "extremely user-friendly" despite its complexity5.
Reverb and tremolo types
The Hydra offers three reverb modes and three tremolo modes, selected together on a three-way switch: Spring, Plate or Room reverb, paired with Sine, Harmonic or Vibrato tremolo312. Keeley describes the reverbs as "dreamy and accurate sounding" and the tremolos as "vintage-voiced"2.
| Switch position | Reverb | Tremolo |
|---|---|---|
| 1 | Spring | Sine Wave |
| 2 | Plate | Harmonic |
| 3 | Room | Vibrato |
MusicRadar's reviewer characterized each tremolo type: the Sine Wave setting "evokes vintage guitar amps, with a smooth pulse offering the most conventional tremolo sound," the Harmonic tremolo is deep and heady, and the Vibrato is hard not to love1.
Beyond the basic modes, the Hydra carries Smart Alt Controls for Shimmer, Spring Age and Room/Hall Size, giving each reverb type a secondary parameter to shape2.
Controls, presets and tap tempo
Two footswitches sit on the pedal, one to engage the reverb and one for the tremolo, so the effects can be layered or used alone46. MusicRadar notes this dual-footswitch layout sets the Hydra apart from Keeley's own Verb-o-Trem series1.
- Rate and Depth controls adjust the tremolo speed and intensity14
- Color knob doubles as the selector: a three-way switch selects reverb and tremolo type with the Color knob depressed1
- Three preset locations, with a trio of red LEDs showing which preset slot is active12
- Tap tempo for the tremolo: hold the tremolo footswitch for a second or so, then tap out your tempo1
- Freeze: depress and hold the reverb footswitch to freeze the input signal for infinite sustain1
The tap tempo works on board or remotely through the external tap-tempo input32. An expression pedal connects via the TRS input and can be assigned to any knob on the pedal32. The Hydra can also be used with pro remote switching systems5.
Power and connections
The Hydra runs on a 9V DC adaptor drawing 115mA, which Keeley describes as an ultra low-current design312. There is no battery option in the specifications given.
Connections are standard: L/Mono and Right inputs, stereo and mono outputs, a TRS expression pedal input and a remote switching input1. You can run the Hydra in mono or stereo, run the reverb wet/dry, and pan the tremolo synced or wet/dry1.
The bypass mode is switchable on the fly between true bypass and buffered trails3. If you want reverb tails to ring out after you disengage the effect, use the trails setting rather than true bypass.
Where the Hydra fits: a companion to the Eccos
Keeley designed the Hydra as a companion to its Eccos stereo delay and looper pedal, with which it shares its controls and input/output configuration36. Guitar World's reviewer called it "a companion piece to the Eccos delay"7. The Eccos runs on the same 9V DC, 115mA power spec, and also offers tap tempo and an expression pedal output, so the two pedals sit together on a board as a matched delay-plus-reverb-and-tremolo pair89.
The reverb-plus-tremolo format itself was already established by the time the Hydra arrived: Guitar World notes that type of stompbox "has become a bit of staple represented by the likes of Strymon's Flint, Fender's TreVerb and Source Audio's True Spring," and that Keeley already had its Verb-o-Trem series7.
What reviewers said
MusicRadar's review listed the Hydra's strengths as excellent tremolo and reverb tones, a space-saver of a format, heaps of controls, presets, tap tempo for the tremolo and the expression pedal option1. GearNews' Jef wrote at launch:
"I really like the stereo nature of the Hydra"4
Pedal of the Day found the pedal extremely user-friendly despite its complexity5. In a 2024 review of the Zoma, Premier Guitar referred to the Hydra as "Keeley's excellent U.S.-made Hydra Stereo Tremolo and Reverb," noting it was less expensive than the Flint10. Guitar World's Trevor Curwen reviewed the pedal and reported its price as $/£2497.
For more on the effect types themselves, see the reverb pedals and tremolo pedals pages.
Videos
Pete Thorn
Keeley Electronics
Keeley Electronics
Questions
Does the Keeley Hydra have tap tempo?
Yes. The tremolo has a tap-tempo mode: hold down the tremolo footswitch for a second or so and then tap out your tempo. There is also an external tap-tempo input on the pedal, so you can tap remotely as well as on board.
Is the Keeley Hydra true bypass or buffered?
Both, and you choose. The Hydra has switchable true bypass or buffered trails bypass, and the switch can be made on the fly. That means you can either cut the effect dead when you disengage it or let the reverb tail ring out naturally.
Can the Hydra freeze the reverb?
Yes. Depress and hold the reverb footswitch and the input signal freezes for infinite sustain, a feature MusicRadar highlighted in its review. It works like a hold or freeze pad for ambient swells and drones.
Does the Keeley Hydra work with an expression pedal?
Yes. The Hydra has a TRS expression pedal input, and the expression pedal can be assigned to any knob on the pedal, so you can sweep reverb mix, tremolo depth or any other control in real time.
Is the Keeley Hydra stereo?
Yes. It runs in mono or stereo with standard L/Mono and Right inputs and stereo and mono outputs. You can run the reverb wet/dry, and pan the tremolo synced or wet/dry across the stereo field.
What is the difference between the Keeley Hydra and the Zoma?
The Zoma, released in October 2024, is described as a spiritual successor to the Hydra, also combining stereo reverb and tremolo at $229. The Hydra is a dual-footswitch design with dedicated reverb and tremolo switches, and it launched in 2020 at $249.
Sources (10)
- Keeley Hydra Stereo Reverb & Tremolo review, MusicRadar, 2021-03-29
- Keeley Hydra: New Stereo Reverb & Tremolo Pedal, Premier Guitar, 2020-11-17
- Keeley Hydra Stereo Reverb & Tremolo, Delicious Audio, 2025-10-07
- The new Keeley Hydra Stereo Reverb & Tremolo pedal, gearnews.com, 2020-11-17
- Keeley Electronics HYDRA Stereo Reverb & Tremolo, Pedal of the Day, 2021-02-24
- Keeley Electronics launches the Hydra, Guitar.com, 2020-11-17
- Keeley Hydra Stereo Reverb & Tremolo review, Guitar World, 2021-04-01
- Keeley Eccos Stereo Delay/Looper, Delicious Audio, 2025-05-09
- NAMM 2019: Keeley announces new Synth-1, DDR, Fuzz Bender and Eccos, gearnews.com, 2019-01-24
- Keeley Zoma Tremolo and Reverb Review, Premier Guitar, 2024-11-13
