The Great Eastern FX Co. Obsolete Devices D312A Distortion Filter is a limited-edition analog distortion pedal with an active filter section, designed and built in England by Great Eastern FX Co.1 It combines a hard-clipping distortion circuit built around three rare Soviet D312A germanium diodes with a resonant band-pass filter that sweeps the midrange, letting a player shape everything from tight, focused drive to heavily saturated, vocal-sounding textures.12
The pedal is the second release in Great Eastern FX Co.'s limited Obsolete Devices series, announced in November 2025 and limited to 165 units because the Soviet-era diodes at its core are scarce new-old-stock parts.32
A distortion with a mids-leaning filter
The D312A Distortion Filter pairs a classic hard-clipping gain structure with an integrated band-pass filter. Delicious Audio describes it as "a limited pedal that reimagines classic hard-clipping circuits through the lens of rare, obsolete components," with a "vocal" mid-range character sculpted by the filter.2 RockBoard's PedalPedia describes the filter section as inspired by classic studio filter and synthesizer concepts, producing thick, aggressive distortion that can be sculpted with a resonant low-pass filter control.1
The filter itself is mids-leaning, sweeping from 300Hz to 900Hz. On Guitar Pedal X, Stefan Karlsson noted that beyond the mid-way point of the sweep, "you're largely in sort of cocked wah territory."3
Controls
| Control | What it does |
|---|---|
| Gain | Sets the core output together with Level3 |
| Level | Sets the core output together with Gain3 |
| Frequency | Sweeps the mids-leaning filter from 300Hz to 900Hz3 |
| Depth | Fine-tunes the filter boost, plus or minus; its impact increases the higher the Frequency is set3 |
Delicious Audio notes that the Frequency and Depth knobs together let a player dial in anything from a subtle mid-emphasis to extreme, "cocked-wah" textures reminiscent of stoner rock.2
The clipping: three Soviet germanium diodes
At the heart of the pedal are three NOS Soviet-era D312A germanium diodes, configured for asymmetrical clipping: two diodes on one side of the waveform and one on the other.32 Delicious Audio describes the result as "a distortion rich in harmonic complexity and dynamic response, a significant departure from the symmetrical silicon pairs found in its predecessors."2
"The highlight is of course that Asymmetrical Germanium Clipping - which sound gorgeous in that rich amp-like style."
Karlsson found the asymmetrical arrangement slightly louder, more aggressive and more amp-like than symmetrical clipping, and noted that germanium clipping brings some degree of volume drop that the asymmetry offsets.3
Circuit lineage: DOD250 and MXR Distortion+
The pedal's gain structure follows a classic hard-clipping design. Karlsson describes it as "kind of a little based on the DOD250, but so much more," and places it adjacent to both the DOD250 and the MXR Distortion+, with similar gain and volume levels but richer texture thanks to the filter section and the germanium clipping.34
A limited run in the Obsolete Devices series
The D312A Distortion Filter is the second pedal in Great Eastern FX Co.'s Obsolete Devices series, a line built around rare, discontinued components.3 The run was limited to 165 units because of the scarcity of the D312A diodes.2 It was available from the Great Eastern FX Co. webstore at £249, and Karlsson picked up his unit at Witney Pedal Party 4.3
Because the run was limited to 165 units and the Soviet D312A diodes are long discontinued, this pedal is a scarce, limited edition rather than an ongoing production model.32
What reviewers said
Karlsson's Guitar Pedal X review praised the pedal's rich, amp-like harmonics and complex textural output, while noting one practical drawback: working the Frequency and Depth controls in tandem is not always easy.3 In the site's 2025 round-up of the best new distortion pedals of the year, he called it "a great sounding Filter Distortion enhanced by rare D312A Soviet Germanium Diodes."4
Videos
Great Eastern FX Co.
Noise Generator
Questions
How many D312A Distortion Filter pedals were made?
The run was limited to 165 units, because the core components, the Soviet-era D312A germanium diodes, are scarce new-old-stock parts. It was the second release in Great Eastern FX Co.'s limited Obsolete Devices series, announced in November 2025.
What diodes does the Great Eastern FX D312A use?
It uses three NOS Soviet-era D312A germanium diodes in an asymmetrical clipping arrangement: two diodes on one side of the wave and one on the other. That asymmetry adds harmonics and a slightly louder, more aggressive, amp-like character than symmetrical clipping.
What frequency range does the filter sweep?
The Frequency control sweeps a mids-leaning band-pass filter from 300Hz to 900Hz. Past the mid-way point of the sweep the effect is largely cocked-wah territory, and the Depth control fine-tunes the filter boost, with its impact increasing the higher you set the Frequency.
Is the D312A Distortion Filter based on the DOD250?
Partly. Reviewers describe it as kind of based on the DOD250, and adjacent to both the DOD250 and the MXR Distortion+, with similar gain and volume levels but richer texture thanks to the filter section and the asymmetrical germanium clipping.
Where is the Great Eastern FX D312A built?
It is an analog distortion pedal designed and built in England by Great Eastern FX Co., a maker whose Obsolete Devices series reimagines classic hard-clipping circuits around rare, discontinued components.
What does the Depth knob do?
Depth fine-tunes the filter boost, plus or minus, and its impact increases the higher up the Frequency scale you are. Together with Frequency it dials in anything from a subtle mid-emphasis to extreme cocked-wah textures reminiscent of stoner rock.
Sources (4)
- Distortion Filter D312A by Great Eastern FX Co., RockBoard PedalPedia, 2026
- New (LTD) Pedal: Great Eastern FX Distortion Filter D312A, Delicious Audio, 2025-11-19
- Guitar Pedal X, Guitar Pedal X, 2025-11-19
- Guitar Pedal X, Guitar Pedal X, 2025-12-05
