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Blueshift Spatial Chorus

Based On
Effect Type
Build Difficulty
Blueshift Spatial Chorus printed circuit board

Printed Circuit Board

What's included?
PCB only. Build instructions and parts list can be viewed or downloaded from this page.


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Project description

The Blueshift Chorus is a faithful clone of the BOSS® DC-2 Dimension C—widely regarded as the best stompbox chorus ever made as well as being one of the most coveted Boss pedals out there. It’s never had a proper DIY project due to the sheer complexity and number of components, but those days are over. The Blueshift is the first serious DIY adaptation of the DC-2—and if that wasn’t enough, it’s designed to fit in a 125B enclosure, no larger than the original.

The DC-2 is different from other choruses in that there are actually two clock+BBD pairs, each powered by either the inverted or non-inverted output of a single LFO. These BBDs then modulate the dry signal so that signal “A” reaches its maximum delay time when signal “B” reaches its minimum and vice versa as they criss-cross back and forth. The average remains constant between the two signals and only the space between the two signals is modulated. The DC-2’s effect is often referred to as motionless because it doesn’t have the signature “warble” or unsteadiness of a traditional chorus with a single BBD.

Circuit history

Originally manufactured from 1985 to 1989, the DC-2 was a guitar pedal adaptation of the revered Roland SDD-320 Dimension D rack unit, so the history lesson must begin several years earlier.

1979: Roland SDD-320 Dimension D

Roland, the parent company of BOSS, is primarily known as a designer and manufacturer of synthesizer and pro audio equipment. In 1979, they released the SDD-320 Dimension D, a 2U rack unit for use in studios and in keyboard rigs. It had five control buttons on the front: four preset buttons labeled 1 through 4 and one marked “Off”. There was also a master bypass button (a hard bypass—different from “Off” which just cancels the chorus signal but still passes the dry signal through the pre/de-emphasis filters) and a switch on the back allowing the user to select whether the input should be mono or stereo. The output was always in stereo.

A typical chorus has “Rate” and “Depth” controls. On the Dimension D, each of the presets 1-4 sets one fixed value for Rate and one fixed value for Depth.[1] The initial reaction to this is usually to wonder why they didn’t just put two knobs on there, but most people who have modified either the SDD-320 or the DC-2 to have knobs instead of switches have agreed that the presets are the best positions and the sounds in between are not as useful. In other words: the engineers knew what they were doing with the presets.

The Dimension D remains a legend today. It can be found in any respectable recording studio and its sound can be heard on countless albums from the 1980s to today. It is often not treated as an “effect” so much as an enhancer or sweetener, bringing depth to the stereo field in a much livelier and organic way than the more traditional methods of using two microphones in the studio or putting a 30ms delay between the channels.

1985: BOSS DC-2 Dimension C

In 1985, some enthusiastic and slightly deranged engineer at Roland decided that he should try to adapt the Dimension D for guitar and release it as a pedal in their compact form factor. The result was the most densely-packed BOSS pedal released to date, somehow arranging 100 resistors, 50 capacitors, 13 ICs, 12 transistors, and 11 diodes onto one single-sided through-hole PCB.

The result was a very faithful adaptation of the Dimension D that worked exceptionally well with guitar. While it lacked the stereo inputs of the original, it kept the stereo outputs and even added a new mono mode where it combined the two chorus signals coming from the BBDs if only one output jack was plugged in. It changed the bipolar +/-14V supply down to the standard BOSS +9V supply, and switched out the MN3007/MN3101 BBD and clock combination for the lower-voltage MN3207/MN3102. It retained the four-switch operation from the original, but the presets themselves were slightly different from the SDD-320, simplifying it in such a way that it could be easily mixed down to mono.

From an engineering standpoint, it’s nothing short of a masterpiece. No less can be said of the sound design. It receives consistently high marks from everyone who plugs their guitar into one, especially when using it in stereo mode.

An original DC-2 can still be found secondhand without much trouble on eBay or, but expect to pay between USD $200 and $350 depending on condition and current market conditions.

Clones and adaptations

Behringer CC300 Chorus Space-C

In 2007, Behringer released their version of the Dimension C, called the “Chorus Space-C”. The main difference from the original DC-2 is that you could push more than one of the buttons at once, allowing for some “in-between” settings that were not possible with the original. And the kicker was that the pedal’s retail price was about $30, which made it pretty attractive when put up against an original unit.

As is typical of Behringer, the build quality was atrocious, with cheap hardware and a plastic enclosure lacking any shielding, making them unfit to use in any sort of professional setting. The sound was generally regarded as good (though usually distinguishable from a real DC-2 in a direct comparison) but the units were often not very well calibrated so they lacked some of the headroom of the original. This was compounded by the fact that they used a lower supply voltage for the BBDs than the original (5.6V instead of 6.8V) which further reduced the maximum headroom.

They were discontinued sometime during 2014-2015 and now fetch secondhand prices of between $80 and $100.

Fromel Seraph

On the other end of the spectrum from Behringer, there is Fromel Electronics. In 2008, John Fromel got curious and went down the DC-2 rabbit hole. He emerged with the Lush, a handmade adaptation of the DC-2, later renamed to the Seraph for legal reasons. The Lush/Seraph was a highly customized production. Each enclosure was acid-etched with unique artwork, and many of them had custom features such as stereo in/outs or an option to use knobs instead of switches. At $300, they weren’t cheap, but you knew you were getting a quality piece of equipment made by someone who had done a great deal of research to make the most accurate clone possible.

The original Seraph was discontinued in 2012. In 2018, an updated version was released called the Seraph Deluxe.

Notes & references

  1. I’ve read from some sources (e.g. this post at Fractal Audio) that there is some additional interaction between the channels in modes 1-3 where the BBD signal from the “L” input is fed into the “R” output and vice versa, and mode 4 restores this to L→L and R→R. The original factory schematic is very difficult to read, and the Dimension D owner’s manual makes no mention of this behavior, so I can’t confirm this—but if anyone knows how this works and can provide a redrawn schematic of the switching portion of the circuit, I would be very grateful.