December 8, 2019

Pedalurgy: What’s a Belton Brick reverb?

The definitive article on reverbs built with the Accutronics Digi-Log module.

Various Belton Brick Reverbs

Spring reverbs that are built with Belton Brick modules are often maligned, as well as heavily praised. Every day there seems to be another reverb on the market that’s built on this chip set. The article below will answers your questions about Belton-Brick reverbs and suggest pedals based on your needs.


What’s a Belton Brick?

In 2007, Brian Neunaber (of Neunaber pedal fame) patented spring-reverb-in-a-module. Solder a few parts to it and you have a competent reverb that rivals the sound you get from a electromechanical spring reverb tank in a Fender amp. The Belton Brick is not the module’s real name. It’s the Accu-Bell BTDR Digi-log and sells for about $15. Interestingly, Brian hasn’t used the Belton Brick in any of his own Neunaber pedals. For a taste of the sound, check out the Battle of the Beltons video from The Pedal Zone.

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What’s reverb?

The concept of reverb is based on natural sound bouncing around in a room. Reflections off the wall come back to your ears much quicker than an echo in a canyon and are more complex. If you put yourself in the middle of a large tiled room and clap your hands, you’ll hear reverb bouncing back to your ears off the walls in front of you, behind you, to the sides and maybe off the ceiling and floor. For argument sake, let’s say there are three distinct reflections coming back to your ears all at slightly different times, since the walls and ceiling are different distances from you. Then come the quieter reflections of those reflections bouncing back, which now make nine and the quieter reflections of those reflections bouncing back that now make 27 and so on. This mix of ever-quieting and ever-multiplying sounds is what we identify as reverb. It’s what spring reverb was built to imitate.

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What’s spring reverb?

Though Bell Labs patented spring reverb, it was Hammond Organ that gave it a practical use. To make their organ sound a bit more reminiscent of cathedral pipe organs, Hammond settled on a three-spring tank. They put a transducer (like a speaker) on one end of the springs to vibrate them and a transducer (like a microhone) on the other end to pickup the vibration. Since the springs were all slighly different length and tension, there was a few miliseconds difference in the time the vibrations took to arrive at the pickup, giving the impression of different reflection distances. This electro-mechanical reverb is not as organic as natural reverb, but has the advantages of being able to be mixed loud and overdriven or fed back into itself for a longer dwell.

In 1961 Leo Fender built one of his studio reverb units into an amp for Dick Dale. And that started it all.

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Why is the Belton Brick known as a “spring reverb in a box”?

Brian Neunaber developed this reverb module by cascading three PT2399 digital delay chips and a few comb filters. Delay times range from about 30-40ms, which are about the same delay times of the three springs in an old Fender Amp reverb tank. Feedback inside the circuit of the module creates a decay similar to wall reflections.

Reverb decay time has an official designation: The length of time it takes the reflections to decrease to -60db. The Belton Brick chips vary in decay time and by module version.

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Are there different Belton modules?

There are three models with variations that put the number at 14. BTDR-2 is a bit smaller and easier to work with than the bulky, original BTDR-1. BTDR-3 modules have discrete delay chips and a patented summing and feedback network that allows for a longer decay and can simulate room size.

Model Decay Time
BTDR-1 S 2 sec
BTDR-1 M 2.5 sec
BTDR-1 L 2.8 sec
BTDR-2 S 2 sec
BTDR-2 M 2.5 sec
BTDR-2 L 2.8 sec
BTDR-3 .5 sec to 3.2 sec

All these modules also have separate horizontal or vertical mounts for where the pins extend. This allows them to more easily fit into various circuit designs or pedal boxes.

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What’s a PT2399 delay chip?

It’s an “analog voiced” digital delay chip, sort of a middle ground between bucket-brigade analog delay chips and DSP (digital signal processor) delay chips. Like a DSP-based delay, the signal is converted to digital in the PT2399 chip. While DSP circuits can craft the effect further while the signal is digital, the PT2399 delayed samples are converted back to analog for effects and tonecrafting.

PT2399 circuits start to sound static-y and lo-fi when pushed to their maximum delay time of about 340ms. Since the delay time is set at near the minimum of 30ms, the three PT2399 chips in a Belton Brick can create a very clean-sounding reverb.

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Why do Belton Brick reverbs all sound similar?

While you can do all manner of manipulation of sound going into and out of the Belton module, parameters of the delays inside the Brick are fixed. The Brick model with the longest decay approximates the long, 3-spring unit traditionally used by Fender with the delays about 30-40mm long. This approximates the feel of playing in the middle of a 40-foot by 35-foot room with a 15-foot ceiling and a carpeted floor. No matter how you process the sound of a Belton Brick, the delays remain the same length. This gives it the signature, slightly-metallic spring sound.

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How do first and second generation Belton reverbs have Decay knobs?

They mix the effect signal from the output of the module back into the input creating a feedback loop. (The third generation of Beltons have an internal feedback loop for variable decay.) Pedal builders may also add a secondary delay into the mix circuit.

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Why do Belton Brick reverbs sound modulated at higher settings?

This occurs naturally, the result of the varying delay times and decay levels of the network of PT2399 chips. It can be made more of less obvious through equalization. This is similar to natural modulation that happens with three-spring reverb tanks.

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Why do some Belton pedals sound glassy and others sound like a cave?

This is usually controlled by a fixed EQ setting or a tone control before/after the Brick in the circuit. Caroline Guitar’s Meteore was crafted to sound like the tile walls of a Paris Metro Station. Others cut treble to sound more dark.

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What’s the difference in Belton Brick reverbs vs DSP reverbs?

Both are digital, but the Belton Brick has more parameters locked down specifically to sound like reverb, so you have limited control over them. Once the signal is converted to digital in a DSP reverb, the builder can do all manner of processing to it before converting it back to analog, like adding lingering decay times.

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Which sounds better, Belton Brick or DSP reverb?

It’s preference. Both can sound great and many players have both on their board. This allows them to use both reverbs for their strengths. DSP’s can create a fantasy environment that’s fat, dusty and ambient. Because Beltons will always have certain restrictions based on natural acoustic properties of the fixed delays and controlled decay, they tend to sound thinner, metalic and more real, due to the tangible room size they create.

DSPs usually have a clean, high-fidelity sound and are very flexible in the reverberated environments they can create. DSPs can border on sounding synthetic, since bulders and players can manipulate the parameters well beyond the limits of natural acoustics. In recent years, pedal builders have hit upon DSP algorithms that sound very close to a physical spring tank. Curiously many players then assume there’s a Belton Brick inside.

Belton Brick reverb circuits can be made to sound more lo-fi, which can be considered a good thing. (Neither natural reverb in a room nor spring tanks are full-spectrum hi-fi, since walls bounce and springs vibrate some frequencies back louder than others.) The signal from the PT2399 chips require filtering to remove noise, which makes the Brick sound more lo-fi and warm. Because of the fixed delays, Beltons also can create a room size that’s more easy to visualize.

The current trend among pedalmakers is mutant Belton Brick reverbs that add distortion, modulation, delay etc. before and after Belton Brick chips. These were formally the realms of DSP. But no matter what you do to a Belton signal, it usually still is recognizable as a Belton.

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What reverbs are built on Belton Bricks?

The lists below are reported to contain Belton Bricks. I’ve opened some up to see if there’s a Belton inside. (Don’t try this at Guitar Center. They don’t seem to appreciate the curiosity.) These lists are by no means complete, but the pedals listed may be easier to find. The order of the lists move from simple to complex. I’ve tried to spare you from videos riddled with ads when possible.

Springy Beltons.

These Belton Brick reverbs focus on emulating the standard Fender spring tank sound. They’re a good choice if you’re looking for vintage sound, surf flavor or just basic, dependable reverb without extended ambience. All springs listed here have a effect volume knob.

  • Cusack Music Reverb SME The Size Modulation Emulator is based on a revised BTDR3 with a separate dry knob as well as Room Size and Texture (tone) knobs. Video
  • Cusack Music Sweet Verb is also based on a revised BTDR3 with speparate wet and dry knobs as well as room Size and wall Texture. Video
  • Hermida Reverb v1, v2 This discontinued circuit was originally built for Santana. It just has a Mix knob for a Fender spring reverb flavor. Probably the most subtle reverb listed here. Video
  • Malekko Spring Chicken v2 This was an early Belton reverb that’s now discontinued. The Cluck (volume) knob on top is joined by a Dwell trimmer on side. Video
  • Mojo Hand Dewdrop This has Mix, Dwell and Tone knobs, but never gets carried away. Video
  • Mowery Electronics Das Vurb This adds a Damp (tone) knob. Video
  • Noise Therapy FX Delirium Sedate spring with one-knob. Video
  • Pedal Monsters Well This is a basic pedal was the forerunner to the Galaxy. It’s now discontinued. Video
  • Chris Ray Premium Effects Tunnel Runner This is a larger-than-life Belton spring based on the BTDR-3 with separate Decay and Feedback knobs. Video
  • Rockett Boing One knob that mimics the Fender amp reverb tank. Video
  • Solid Gold Surf Rider III is a surf-genre focused reverb with knobs for tone fine-tuning. The Boost footswitch kicks the reverb level up. Video
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Ambient Beltons.

These extend the decay get long but, don’t self-oscillate.

  • Earthquaker Devices Levitation v2 has a Tone knob that’s more of a bass boost. The Atmosphere knob pumps upper frequencies back into the decay for a more harmonically-rich effect. Also has a Short/Long toggle that makes the pedal spring or ambient. Video
  • noiseKICK FX Gregg’s Place Three knobs: Baileys (mix), Creamy (tone) The Funk (decay). It gets big. Video
  • Pedal Monsters Galaxy Three knobs: Mix, Tone and Decay. Video
  • VFE Springboard This uses the BTDR-3 chip has low-and-high damp to control length as well as has separate Bass and Treble knobs. Video
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Self-Oscillating Beltons.

These let you turn up the decay to the point of feedback, but don’t introduce excessive distortion in the process.

  • Death By Audio Reverberation Machine The Altitude knob adds fuzz to the dry signal. It has a Bright/Dark switch to control tone. video
  • Hungry Robot Stargazer v2 is two reverbs in one: one dark, the other sparkly. They can both get ambient and can be used together or separately. Cranking the Decay knob sends the reverb into self-oscillation.
  • Hungry Robot Little Gazer is a stripped down version of the Stargazer. The switch controls whether the reverb is sparkly or dark. It’s been discontined. Video
  • Mantic Proverb XS is the original Proverb in a smaller box. The Dwell knob kicks in the self-oscillation. Video
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Beltons With a Feedback Footswitch.

Some pedal makers add momentary foot switches for easy control of self-oscillation.

  • AC Noises AMA This Italian reverb gives you the option of adding analog feedback oscillation and bit crushing after the reverb. With the Mix knob clockwise you get 100% wet. Video
  • Caroline Guitar Meteore Modeled after the natural acoustics of a vintage Paris Metro station, this reverb has a Havoc footswitch and analog overdrive on reverb. It also has Decay and Regen knobs.
  • Electronic Audio Experiments Beholder Aberrant Reverberator puts reverb before a high-gain fuzz. The Drone footswitch increases loop feedback. video
  • Mantic Proverb The latest version has an expression pedal jack and oscillation footswitch. Video of original Proverb.
  • Solid Gold Effects Counter Current is a distorted version of the Surf-Rider III designed to distort and feedback. When you crank it, the reverb starts to sound like a smooth fuzz. The Feedback footswitch brings up the oscillation, but has some form of limiting that keeps from oversaturating your amp. Video
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Belton Reverb + Delay.

Adding a delay to the Reverb opens up more ambient possibilities for those who love the spring sound. These are often grittier than DSP reverb + delay pedals.

  • Discomfort Designs Passage Through the Hollow Earth Not exactly a combo, but uses a PT2399 chip as a predelay before the Belton Brick. Slapbacky and lo-fi, the Everblast footswitch maximizes the effect. Video
  • EQD Ghost Echo v3 adds a slapbackish delay from a PT2399 chip to the mix. This can be subtle or bold, with the Attack knob acting as a pre-delay. It self-oscillates with the Dwell knob at max. Video
  • Hungry Robot The Wash crossfeeds a Belton Brick and an 1100ms PT2399 delay into a wash of ambience. Video
  • Make Sounds Loudly Valyrian Doom Ambient Reverb adds a delay to the mix with delay time controlled by the Pre-Delay knob.
  • Quiet Theory Prelude is the most smoothly ambient of the batch with separate level knobs, tone switches and foot switches so the delay and reverb can be used independently. Also has a momentary burst mode of each effect. Video
  • VFE Yodeler marries a BTDR-3 Brick with a full-fledged PT2399-based delay for an all-analog circuit. They can be run in series, parallel or together. Video
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Beltons With Effects Loops.

These Belton Brick reverbs have effects loops so you can add modulation, delay or other effects to the mix.

  • Coppersound Pedals Daedalus This pedal from Greece uses a BTDR3 Brick. The expression jack works with a controller pedal or as an effects loop. The Preamp knob Intensifies decay can add drive to a pedal in the loop. The Reverb II switch and knob allow for an alternate setting. Video
  • Jonny Rock Gear Moby Depth has a loop and a Regen knob to feed the signal back into the reverb for a longer decay. Video
  • Orion Effecte Kafka from Germany has an effects loop and adds germanium pre-stage fuzziness for a reverb that can get really gritty. The Reflexion knob turns loose the self-oscillation. Video
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Mutant Belton Reverbs.

These are Belton Brick reverbs with added superpowers.

  • Hungry Robot El Castillo mixes an ambient reverb with a pitch-shifted delay up to a second long. Video
  • Hungry Robot Starlite v1, v2 This combines an ambient Belton brick reverb and tremolonic modulation on the reverb only. v2 adds a knob to control the ramp of the waveform. Video
  • Rockett Mr Moto Mild and definitely surfy, this reverb adds an exceptional tremolo on the reverb only. Video
  • Ezhi & Aka Terverb from Russia uses three Belton bricks. It has a vibrato, tremolo and many droning possibilities, as well as a touch-sensitive pitch dropper. Video
  • Fox Pedal Magnifica Deluxe has two beltons reverbs that can be stacked or used separately for extra springiness. Video
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Which Belton Brick reverbs would you recommend?

Below are a few I own and love. I suggest you view the video links if you want to get to know any of these pedals to see if they sound good to your ears and fit your needs.

  • Springy: Rockett Boing You can’t go wrong with Boing for a basic spring. It’s flawlessely tuned for that big Fender tank sound. With just one knob to mix in the reverb, it can go from subtle to surfy, but never buries the dry and sounds gorgeous at any setting. It’s a leave-it-on reverb that you’ll forget is there…until you turn it off and your axe suddenly sounds like your amp is in a dollhouse. Put it at the end of your chain and even a DSP reverb before it can sound more live. Video
  • Self-Oscillating Reverb: Hungry Robot Stargazer This reverb offers a broader range of possibilities with two, beautiful-sounding reverbs that can be used together or independently. Both give you a big, boomy room, with a darker, hall-style Red channel and a sparkly, modulated Blue channel. Both channels can self oscillate. Each channel has a footswitch, so this pedal is useful for easy, live switchup of three different reverb settings (dark, sparkly and mixed). Video
  • Feedback Footswitch Reverb: Solid Gold Counter Current This one gets ambient with the Decay knob and distorted with the Drive knob, but doesn’t self-oscillate until you hold down the feedback footswitch. It has a bit of distortion, even with the Drive knob at 7a and a more-than-subtle blend even with the Level knob at 7a. Where it really excels is with a clean tone by putting all the distortion on the reverb. Video
  • Mutant: Hungry Robot El Castillo I’m almost reluctant to recommend this arpeggiating reverb since a majority of its dark fairytale tricks can be discordant. If you like to set-and-forget knobs, this probably isn’t for you. This combines a Belton Brick reverb with DSP pitch-shifted delay. The combo of the two can give you a hint of angelic chorus, doppler drops, ascending or descending arpeggiations and organ echoes, as well a complete discordant mayhem. Video
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How easy is it to build my own Belton Brick reverb?

If you’re curious about pedal building, Belton Brick reverbs are easy to build if you have any experience with building circuit boards and own a soldering iron. Even easier, the legendary DIY Rub-a-Dub reverb or the Rub-a-Dub Deluxe are available as preprinted circuit boards. You can also buy Belton Brick reverbs in a kit with all holes pre-drilled in the box and all parts included. (Note that I haven’t built this particular kit myself.)

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