ALM Stereo Sum (2023–)

A no-nonsense 4HP summing hub that quietly becomes the backbone of your stereo patching—until you realize you can’t live without it.

Overview

Patching a stereo signal into two separate mixers works until you run out of space. The ALM Stereo Sum fixes that. It doesn't boost and it doesn't color - it just sums. Four stereo input pairs, each pair summed independently to one of two stereo outputs, or all eight inputs sent into a single master mix via normalization.

This isn't a mixer with faders or pan controls. It's a utility, a junction box for stereo signals, with some clever internal routing. The top half's outputs are normalized to the bottom half, so if you leave the top output unpatched, those two stereo inputs get folded into the lower mix. You can treat it as two independent 2-stereo-input mixers, or chain them into one big 4-pair combiner. It's DC-coupled, so it doesn't care if you're mixing audio or CV - LFOs, envelopes, modulation streams, whatever. It sums them all the same way.

Made in England and built to ALM's usual skiff-friendly standards: 32mm depth, reverse power protection, minimal current draw. It fits behind other gear or in tight cases without trouble. Typical jobs are merging the returns from a pair of stereo effects or combining multiple stereo VCO stacks.

Specifications

Manufacturer	ALM Busy Circuits
Production Years	2023–
Original Price	£75 GBP
Module Height	3U
Width	4HP
Depth	32mm
Power Supply	+12V / -12V
Power Consumption	+12V 8mA / -12V 8mA
Input Type	Stereo (Dual Mono), Normalled
Number of Inputs	4 Stereo Pairs (8 Total)
Output Type	Stereo (Dual Mono), Normalled
Number of Outputs	2 Stereo Pairs (4 Total)
Gain	Unity (0dB)
Coupling	DC-Coupled (Audio and CV Compatible)
Normalization	Top Output → Bottom Input Section
Panel Color	Silver
Country of Origin	England
Model Number	ALM038

Key Features

Flexible Dual-Mixer Architecture

The top two stereo input pairs feed their own mix output, and the bottom two do the same. Patch a cable into the top output and that path breaks free. Leave it open, and those signals cascade down into the lower mix. So you can use it as two isolated 2-input stereo mixers, or as a single 4-pair summing hub. That suits merging stereo effects returns or layering multiple stereo VCO outputs without eating up panel space.

DC-Coupled for Audio and CV Mixing

Most summing mixers assume you're only dealing with audio. The Stereo Sum is fully DC-coupled, so it handles control voltages just as cleanly as audio signals. That allows summing multiple LFOs for complex modulation, blending envelope generators, or combining sequenced CV streams before feeding them into a VCA or filter. Some users even repurpose it as a passive mult of sorts, using the left-to-right normalization on inputs to duplicate a mono signal across both channels. It's not a true mult, though, so high-impedance sources should be approached with caution.

Skiff-Optimized and Power-Efficient

The Stereo Sum is 4HP and 32mm deep. It draws a mere 8mA on both rails, making it one of the most power-efficient active mixers in the Eurorack world. There are no knobs and no switches, just labeled jacks. The panel is silver anodized aluminum, and the module includes reverse power protection, so a misrouted power cable won't fry it.

Historical Context

The Stereo Sum arrived in 2023 as part of a wave of utility-focused modules from ALM Busy Circuits, a UK-based designer known for function-first Eurorack gear. While many manufacturers were chasing complex modulation or digital wizardry, ALM stuck with the plumbing - modules that solve real patching problems without overengineering. The Stereo Sum doesn't try to be a mixer, a processor, or a sound generator. It's a summing junction.

It sits alongside compact mixers like the Intellijel Mixer 4, the Mutable Instruments Vectron Mix, and the Doepfer A-138p, but it focuses exclusively on stereo pairs and normalization. Unlike those modules, it has no level control, just unity-gain summation. That makes it more of a behind-the-scenes workhorse than a performance tool. Its closest sibling might be the ALM MEGA-TANG, a VCA/mixer combo it's often paired with. The Stereo Sum fills a gap that module doesn't: combining stereo sources without CV control or coloration.

Collectibility & Value

As a recent release, the ALM Stereo Sum isn't a vintage collectible yet. New units sell for around £75 GBP (or ~$95 USD), with European retailers listing them for €88. There's no secondary market premium. Prices stay close to retail, and used units typically go for 20-30% less.

Failures are rare. There are no active components prone to drift, no pots to wear out, and no complex circuitry to debug. The most common issue reported is accidental overloading - patching hot signals into multiple inputs and clipping the output stage - but that's user error, not a design flaw. Because it's passive in function (unity gain), it doesn't color or distort. When buying used, check for cold solder joints or jack misalignment, especially if the module shows signs of heavy use.

For buyers, the real value isn’t in resale—it’s in utility. If your system lacks a clean way to merge stereo effects, combine layered voices, or sum CV streams, the Stereo Sum pays for itself in patching clarity. It’s not a flashy centerpiece, but it’s the kind of module you’ll find yourself reaching for daily.