The KMA Machines STEREO ABY is a passive stereo ABY switcher: a box that routes one stereo signal to two separate destinations, or combines two stereo signals into one, at the tap of a footswitch. KMA describes it as a "Passive Stereo AB/Y pedal with active switching," meaning the audio path is fully passive while a separate powered circuit drives the relay-based soft switching1.
KMA frames the pedal around a simple idea: the company asked itself "why is it so difficult to find a simple ABY in a stereo format?" and built the STEREO ABY with a focus on "durability, reliability, simplicity and hassle-free operation"2. It is made in Berlin, Germany, in a compact enclosure with top-mounted jacks1.
A passive stereo ABY with relay switching
The core of the design is the split between the audio path and the switching. The audio signal is entirely passive, which KMA says means "the audio signal itself is entirely untouched and without any colouration"1. The active part of the pedal exists only to operate the switches: it uses "Active silent relay-based soft switching, heavily reduces mechanical noise and pops"1. For a player, that means the loud mechanical click of a passive footswitch and the pop that can come with it are reduced, while the tone passing through stays as it went in.
The bypass is listed as True Bypass, so when a path is not selected the signal does not sit in the pedal's electronics1.
Splitting and combining stereo signals
The STEREO ABY works in both directions. KMA describes it as able to "switch or combine your stereo input signal between two separate destinations or switch or combine" two signals into one1. In practice that covers two common jobs:
- One into two: send a single stereo source, such as a stereo delay or reverb output, to either of two stereo destinations, or to both at once.
- Two into one: combine two stereo signals into a single stereo output, switching between them or running both together.
Because the audio path is passive, the pedal does not buffer or isolate the signals; it simply routes them1.
Controls and LEDs
The pedal's status is shown by three LEDs, using the same color scheme across KMA's ABY series13:
| LED | Meaning |
|---|---|
| Red | Signal path A selected |
| Yellow | Signal path B selected |
| Blue (center) | A and B selected together |
Mono, stereo and active versions
The STEREO ABY sits in a four-pedal family. KMA points mono players to the KMA Machines ABY, the mono version of the same passive concept: "Don't need stereo? Then the KMA ABY is for you!"1. For players who want active electronics, there are two active versions.
| Model | Audio path | Extra controls | Weight |
|---|---|---|---|
| STEREO ABY | Fully passive, true bypass | None listed | 260 g / 9.17 oz1 |
| Active STEREO ABY | Fully active, silent switching | 180° Phase switch, A&B>Y or Y>A&B switch | 185 g / 6.53 oz3 |
| Active ABY | Mono active counterpart | Phase and direction switching | Not listed here |
The Active STEREO ABY adds a 180° Phase switch that flips the A channel, which KMA says "can prevent signal cancellation and tone issues" when combining or splitting signals, plus an A&B>Y or Y>A&B switch for choosing the direction the pedal works in3. It draws more than 55 mA, against the passive version's more than 40 mA, and both run on 9 V DC center negative 2.1mm supplies13. The active mono counterpart is the KMA Machines Active ABY3.
The STEREO ABY needs a 9 V DC power supply even though its audio path is passive: the power runs the relay switching circuit and the LEDs, so it cannot run without power1.
All four pedals share the same enclosure size, 56 mm high, 112 mm wide and 65 mm deep, with top-mounted jacks that KMA says "will fit into any setup"13. The passive STEREO ABY is the heavier of the two stereo versions at 260 g, against the Active STEREO ABY's 185 g13.
For more on this category of pedal, see switching pedals.
Questions
Is the KMA Machines STEREO ABY true bypass?
Yes. KMA lists the STEREO ABY as True Bypass, with a fully passive audio design so the signal itself is untouched and without coloration. The switching is handled by a separate active circuit using silent relay-based soft switching, which reduces mechanical noise and pops when you change paths.
Can the KMA STEREO ABY split and combine stereo signals?
Yes. It works in stereo in both directions: one stereo signal into two separate destinations, or two stereo signals combined into one. KMA notes it can switch or combine your stereo input signal between two separate destinations, or switch or combine two signals into a single output.
What do the red, yellow and blue LEDs mean?
The LEDs show which signal path is engaged. Red means path A is selected, yellow means path B is selected, and the blue LED in the centre means both A and B are selected at once. The same color scheme is used on the Active STEREO ABY.
What power does the KMA STEREO ABY need?
It runs on 9 V DC with a center negative 2.1mm plug, with a maximum current draw of more than 40 mA. The power feeds only the active switching circuit and LEDs; the audio path itself is fully passive, so the signal is never colored by the electronics.
What is the difference between the KMA ABY and the STEREO ABY?
The KMA ABY is the mono version of the same passive switching concept, for players who do not need stereo. The STEREO ABY handles stereo signals in both the one-into-two and two-into-one directions. KMA also makes active versions of both, which add a 180 degree phase switch and an A&B>Y or Y>A&B direction switch.
How much does the KMA STEREO ABY weigh?
It weighs 260 g, or 9.17 ounces, in an enclosure measuring 56 mm high, 112 mm wide and 65 mm deep. The Active STEREO ABY is lighter at 185 g (6.53 ounces) in the same enclosure size.
Sources (3)
- STEREO ABY, KMA Machines
- Introducing our New ABY pedals, KMA Machines
- Active STEREO ABY, KMA Machines
