The Wren and Cuff De La Riva BM20-Ultra is a fuzz pedal built as a deep take on the Electro-Harmonix Big Muff Pi. What sets it apart from most Muff-inspired pedals is that it does not lock you into one fixed circuit: through a combination of DIP switches and toggle switches, you can design the gain stages of the pedal yourself, reshaping the character of the fuzz1.
The classic Big Muff circuit is built in five stages: an input/gain stage, a first clipping stage, a second clipping stage, a tone stage, and an output stage2. The BM20-Ultra takes that familiar platform and makes the parts other Muffs hardwire, adjustable.
A Big Muff with designable gain stages
On the surface, the BM20-Ultra keeps the control layout a Muff player expects. Its three knobs replicate the gain, tone, and output controls of the Electro-Harmonix original3. The real flexibility lives in the switches:
| Control | What it does |
|---|---|
| 3 knobs | Gain, tone, and output, matching the original Big Muff layout3 |
| 2 sets of 10 DIP switches | Affect the tone by letting you design the pedal's gain stages1 |
| 2 toggle switches | Turn the two transistors, silicon and germanium, on and off1 |
The transistors themselves are a deliberate departure from vintage parts. High-gain MPSA18 transistors in plastic housings replace the original's metal-can 2N5133s3. Delicious Audio describes the design as inspired, in all likelihood, by the Tech 21 SansAmp stompbox and by Chase Bliss Audio's use of DIP switches1.
Build-wise, Premier Guitar's reviewer found the pedal solidly made inside and out, noting an unusual-looking circuit board that houses both tiny surface-mount components and traditional through-hole parts, including the four transistors3.
There is no battery compartment, and the 9V adapter is not included, so you will need a power supply before the pedal is usable3.
What reviewers said
Premier Guitar's 2023 review was emphatic about where the BM20-Ultra sits among tweakable dirt pedals3:
"Wren and Cuff's De La Riva is one of the most complex and open-ended distortion pedals ever created, right up there with the trickiest gizmos from Origin Effects and Chase Bliss."3
Delicious Audio, covering the pedal in 2019, called it "the ideal pedal for the true Muff connoisseur, allowing for a nearly infinite number of tonal possibilities," and said the device looks and sounds impressive1. The same piece summed it up as "a true muff lovers dream with a near endless palette of possibilities at your fingertips"1.
How it fits among Wren and Cuff's Muffs
Wren and Cuff builds a wide range of Big Muff variations, from recreations of specific vintage circuits to signature models. The BM20-Ultra is the company's most configurable take on the Muff, where pedals like the Tri Pie '70 or the Box of War aim at particular vintage voicings. If you want a fixed, period-correct Muff sound, those pedals do that; if you want to design your own gain structure, the BM20-Ultra is the one built for it1.
Videos
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Questions
Does the De La Riva BM20-Ultra take a battery?
No. There is no battery compartment inside the pedal, so it needs an external power supply. It runs on standard 9V power, and the adapter is not included with the pedal.
Is the BM20-Ultra true bypass?
Yes. The pedal uses true bypass switching, so when it is off your signal passes through without active circuitry in the way.
Is the BM20-Ultra analog?
Yes. Delicious Audio describes it as 100% analog in all ways, with no digital processing in the signal path.
What do the DIP switches do on the BM20-Ultra?
The two sets of 10 DIP switches let you design the gain stages of the pedal, reshaping its tone. Combined with the two toggle switches that turn the silicon and germanium transistors on and off, they open up a wide range of Muff voicings.
Where is the BM20-Ultra made?
It is made in the USA by Wren and Cuff. Premier Guitar's reviewer found it solidly made inside and out, with a circuit board that mixes surface-mount and through-hole parts.
What transistors does the BM20-Ultra use?
It uses high-gain MPSA18 transistors in plastic housings, replacing the metal-can 2N5133 transistors of the original circuit it is based on. Two toggle switches turn the silicon and germanium transistors on and off.
Sources (3)
- Wren And Cuff De La Riva BM20-Ultra Fuzz, Delicious Audio, 2019-06-24
- BIG MUFF TRANSISTORS AND OTHER COMPONENTS, Kit Rae (kitrae.net), 2011
- Wren and Cuff De La Riva BM20-Ultra Review, Premier Guitar, 2019-08-16
