AMS Chorus 2 ()

A rare digital add-on that haunted the studio racks of the 1980s, giving sterile digital delays analog-style modulation

Overview

Turn it on and nothing happens. No blinking lights, no sweeping LFOs, no obvious movement. Patch it in, though, and the AMS DMX 15-80S isn't just repeating a signal anymore. It sways. That's the AMS Chorus 2: not a standalone synthesizer, not even a full effect unit, but a modulation add-on for one of the most revered digital delays of the early digital era. It doesn't make sound. It makes sound *move*. The lush background vocals on a Peter Gabriel record and the stereo spread on a Trevor Horn production are the kind of thing the Chorus 2 was built to do.

Advanced Music Systems (AMS) never sold the Chorus 2 as a consumer product. It was a specialized controller module, an add-on for the AMS DMX 15-80S and S-DMX digital delay units, designed to give a richer, more organic stereo image through precise pitch and delay modulation. The DMX 15-80S could already shift pitch and repeat signals with digital clarity, but it lacked the subtle, continuously varying modulation that gave analog tape echoes and bucket-brigade delays their warmth. The Chorus 2 added a sinusoidal VCO to modulate the delay lines. The result was a stereo chorus effect that mimicked the natural pitch wobble of doubled vocals or instruments.

Despite the name, the Chorus 2 wasn't the first AMS chorus unit. Earlier versions like the DMX Chorus Controller (sometimes called the Chorus 1) existed in limited forms. The Chorus 2 was a refinement, with two independently controlled modulation channels and precise depth and rate control. It was also one of the rarest. It was never mass-produced and was typically sold as a factory upgrade or bundled with high-end studio installations. Most units went to broadcast studios, major recording facilities, or elite producers who wanted the widest stereo imaging possible. Fewer than a few hundred are believed to have been made, and even fewer survive in working condition today.

Specifications

Key Features

The Modulation Engine

The Chorus 2 doesn't generate sound. It manipulates time and pitch in real time. A low-frequency sine wave is applied to the delay time of each channel, which makes a subtle, continuously varying pitch shift that mimics the natural inconsistencies of human performance. The stereo image doesn't just pan left and right, but *pulses*, with one side slightly ahead and lower in pitch, then the other. The Rate and Depth controls let engineers dial in anything from a gentle shimmer to a pronounced, almost flanging-like sweep. Unlike a flanger, the Chorus 2 works on true pitch and delay variation, not all-pass filtering, which gives it a more natural, less metallic character.

Independent Channel Control

What set the Chorus 2 apart from later rack chorus units was its dual-channel independence. Each modulation path (A and B) could be adjusted separately. Engineers could set one channel to a slow, deep sweep and the other to a faster, shallower one, creating a swirling, three-dimensional effect that became a signature of 1980s pop and art rock productions. The stereo spread control adjusted the phase relationship between channels to avoid cancellation in mono. That mattered for broadcast and vinyl mastering, where phase coherence was non-negotiable.

Seamless Integration with the DMX 15-80S

The Chorus 2 didn't plug into an effects loop. It became part of the DMX 15-80S, connecting via a DB25 cable to the unit's internal control bus. Once installed, it took over the pitch and delay modulation functions, and it locked out the manual pitch controls on the host unit when engaged. Because the modulation was applied at the digital core level and not as a post-effect, it preserved signal integrity and avoided the latency or degradation that could come from external processing. It also meant the chorus could be used with feedback, regen, and multi-tap delays, for evolving, self-modulating textures that standalone chorus pedals couldn't produce.

Historical Context

The Chorus 2 emerged in the late 1970s and early 1980s, when digital audio was moving from laboratory curiosity to studio reality. The AMS DMX 15-80S, launched in 1978, was the first microprocessor-controlled digital delay, with unprecedented precision in timing and pitch shifting. That clinical accuracy was also its weakness, because engineers missed the warmth and movement of analog tape and BBD delays. The Chorus 2 was AMS's answer: a way to humanize digital precision without giving up control. It wasn't competing with pedals like the Boss CE-2 or the Roland Dimension D. It operated in a different price class, where a single unit could cost more than a car.

Its closest competitors weren't stompboxes, but high-end studio processors like the Eventide Instant Flanger, the Lexicon 224, and the Roland SDE-3000. Those units offered chorus as one of many effects. The Chorus 2 was a single-purpose tool. It was also developed in parallel with BBC broadcast standards, which demanded rock-solid reliability and phase-accurate stereo imaging, and those requirements shaped its conservative, no-frills design. It had no presets, no flashy displays, no MIDI. It was built to be patched in and set.

Collectibility & Value

Today the AMS Chorus 2 is a unicorn. Even among vintage synth collectors, it's rarely seen and more rarely understood. Most listings on the secondhand market are mislabeled - sold as "AMS Chorus" or "DMX Chorus Controller" without confirming the model number. A genuine Chorus 2 in working condition can command between $1,800 and $3,000, but only if paired with a DMX 15-80S or S-DMX. Standalone, it's nearly useless, like selling a steering wheel without a car.

Common failures include dried-up electrolytic capacitors in the power regulation circuit (though the unit draws power from the host, it still has internal filtering), failed VCO stability due to aging op-amps, and DB25 connector wear from repeated plugging. Because it lacks user-serviceable parts, repairs require deep familiarity with AMS's proprietary control bus and analog modulation circuits. Service technicians observe that the original ICs, particularly the NE5532 op-amps and discrete VCO components, are still available, but calibration requires access to a working DMX unit for real-time testing.

Buyers should never purchase a Chorus 2 without verifying compatibility with the host unit. Some DMX 15-80S units were never equipped with the internal program interface board needed to accept the Chorus 2, and retrofitting requires replacing firmware chips. That takes technical skill and access to rare components. Documentation shows that AMS offered upgrade kits, but few survive. Prioritize units sold with original DB25 and power cables, and insist on a functional demonstration. It isn't a pedal you can plug into a pedalboard.

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