The 3Leaf Audio Proton is an envelope filter pedal, the effect often called autowah: a filter whose cutoff sweeps up and down with how hard you play, producing the percussive, quacking sound made famous by Stevie Wonder and used by both guitarists and bassists12. Delicious Audio's Paolo De Gregorio describes it plainly: "The Proton is a rather simple pedal born to do one thing: the rhythmic, autowah sound used by both guitarists and bassists"1.
What it does to your sound
The Proton is an optically controlled analog envelope filter1. An envelope filter listens to the dynamics of your playing and moves a filter in response, so notes played harder open the filter wider. It is a close cousin of the wah, but driven by your attack rather than by foot.
The 2015 announcement highlighted a Tone knob for fine control over the filter cutoff frequency, and an increased sensitivity range for better compatibility with low-output instruments, which matters if you run a bass or a guitar with weaker pickups through it2.
Versions: from the first Proton to the MK4
The first iteration of the Proton was released almost ten years before the redesigned second version1. That redesign was substantial. According to Delicious Audio:
"The circuit has been completely redesigned to offer better tone and a more musical response."
What changed in the redesign:
- A new detector circuit1
- A new Range switch allowing much deeper filter sweeps1
- Greatly expanded range that can reach the classic 1970s filter sounds and well beyond1
The current version is the Proton MK4, which the maker describes as "an envelope filter made in the Pacific Northwest from USA 304 stainless steel"3.
Rocket Red limited edition
The Proton MK4 was offered in a Rocket Red edition dated 09.26, limited to an edition of 111 units with a limit of one per customer3. As of October 26, 2026, the maker's product page listed it as sold out3.
The Rocket Red MK4 is a limited run of 111 and is sold out. The standard Proton MK4 remains listed on the maker's site at $366.00 USD3.
Build and bypass
3Leaf Audio's product line uses a relay true bypass system that automatically switches to bypass in the case of power failure, so a dead battery or lost power does not kill your signal2. Earlier Protons shipped in custom folded steel enclosures2; the MK4 enclosure is USA 304 stainless steel3. All 3Leaf Audio products are built in Seattle by musicians2.
Related pedals
3Leaf Audio also makes the larger Wonderlove envelope filter, announced alongside the Proton in 20152, and the GR2 envelope filter. For other takes on the effect, see the filter pedals page.
Videos
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Mike Hermans
Zachary Rizer
Questions
What is the 3Leaf Audio Proton?
The Proton is an analog envelope filter pedal from 3 Leaf Audio, built to produce the rhythmic autowah sound used by both guitarists and bassists. Delicious Audio describes it as a rather simple pedal born to do one thing, and the current MK4 version is made in the Pacific Northwest from USA 304 stainless steel.
Where is the 3Leaf Audio Proton made?
3Leaf Audio products are built in Seattle by musicians, according to the company's 2015 press release. The current Proton MK4 product page says the pedal is made in the Pacific Northwest from USA 304 stainless steel.
How is the Proton MK4 different from the first Proton?
The first Proton was released almost ten years before the redesigned second version. The redesign brought a completely redesigned circuit with a new detector circuit, a new Range switch allowing much deeper filter sweeps, and what Delicious Audio describes as better tone and a more musical response with greatly expanded range.
Does the Proton work with low-output pickups?
Yes. When the Proton was announced in 2015, the press release highlighted an increased sensitivity range for better compatibility with low-output instruments, which matters for players of basses and guitars with weaker pickups.
Is the 3Leaf Audio Proton true bypass?
The Proton uses a relay true bypass system that automatically switches to bypass in the case of power failure, a feature 3Leaf Audio applies across its product line according to the 2015 announcement.
Is the Proton MK4 Rocket Red edition still available?
No. The Rocket Red edition of the Proton MK4 was a limited run of 111 units, limited to one per customer, and the maker's product page listed it as sold out as of October 26, 2026.
Sources (3)
- 3 Leaf Audio Proton Envelope Filter, Delicious Audio, 2021-01-05
- 3Leaf Audio Launches Proton & Wonderlove Filters, Premier Guitar, 2015-10-13
- PROTON MK4 // ROCKET RED, 3 LEAF AUDIO
