The Ethos 60's Harmonic Bias Trem is a tremolo pedal from Vermont-based CustomTone LLC, designed to channel what Delicious Audio's Paolo De Gregorio described as "the swirling, three-dimensional modulation of 1960s Brownface and Blackface Fender amps"1. It is a two-mode design: a standard amplitude tremolo, the kind of volume-based wobble most tremolo pedals produce, and a harmonic tremolo, the phase-shifted, vintage-style circuit found in those old Fender amps, where the treble and bass of the signal swell against each other rather than the whole signal dipping in level1.
Two kinds of tremolo in one box
Most tremolo pedals, like the ones collected on the Tremolo Pedals type page, work by varying the amplitude, the overall level, of the signal. Harmonic tremolo works differently: it splits the signal into frequency bands and modulates them in opposition, which is what gave the Brownface and Blackface Fender amps their distinctive swirling character. The Ethos offers both approaches in one pedal, with two footswitchable modes that toggle between amplitude-based (standard) and harmonic tremolo (phase-shifted, vintage-style), each with its own independent speed setting1.
Guitar Pedal X's Stefan Karlsson, writing when the pedal was announced, called it "A really cool new 2-mode fully analog vintage style Amplitude and Harmonic Bias Tremolo," and described the circuit as a Fender Brown Panel amp-derived harmonic bias tremolo32.
Controls and footswitches
The pedal's controls, as reported by Guitar Pedal X at announcement2:
| Control | What it does |
|---|---|
| Tone | Tone control |
| Volume Trim | Volume Trim control |
| Slow Speed | Slow Speed control |
| Fast Speed | Fast Speed control |
| Intensity | Intensity control |
| Mode | Amplitude / Harmonic |
| Speed footswitch | Slow / Fast |
Delicious Audio's later preview adds detail on how some of these work. The Intensity knob adjusts modulation depth across both modes. The Tone mini-knob and what De Gregorio called the "mysterious" VTrim likely fine-tune high-end response and bias voltage for added vintage authenticity1. Tap tempo is included for on-the-fly rhythmic control1.
The three footswitches give the pedal its compact layout, a format Guitar Pedal X noted was "designed for the effect"2.
Release status and availability
The Harmonic Bias Trem was designed by Vermont-based CustomTone LLC.
Full specifications, including power requirements and bypass type, had not been published as of the November 2025 preview1.
Videos
Tim Lerch
Mike Hermans
Tim Lerch
Sources (3)
- Custom Design Ethos 60's Harmonic Bias Trem, Delicious Audio, 2025-11-05
- Guitar Pedal X, Guitar Pedal X, 2025-06-11
- Guitar Pedal X, Guitar Pedal X, 2025-12-09
