KMA Machines ABY

The KMA Machines ABY is a passive ABY switcher in pedal format: it sends one mono instrument signal to either of two outputs, or both at once, and it works the other way too, combining two inputs into one destination. KMA describes it as a "Passive ABY pedal with active switching," meaning the audio path is fully passive while a small powered circuit handles the footswitch action¹.

That split is the pedal's main idea. The audio signal never passes through a buffer or active stage, and KMA says the practical result is that "the audio signal itself is entirely untouched and without any colouration"¹. Power goes only to the switching, not to your guitar signal.

A passive signal path with relay switching

An ABY box is one of the simplest utilities on a pedalboard, but how it switches matters. Cheap passive ABY boxes use mechanical switches that can pop loudly through your amp. The KMA ABY instead uses "Active silent relay-based soft switching, heavily reduces mechanical noise and pops"¹. The relay still passes your signal passively, but the footswitch itself triggers it softly rather than slamming metal contacts together.

The bypass is true bypass¹, and KMA points out across the ABY Series that the passive models keep it that way, "perfect for fussy vintage fuzz pedals too"². Players who run germanium fuzzes know a buffer in front of one can change its character, so a passive path matters if the ABY sits early in the chain.

The A, B and A&B modes

The pedal gives you three states: output A only, output B only, or both combined. The mode is shown by LEDs, with KMA specifying "Red for A, Yellow for B and Blue in the centre for A&B"¹.

What that means in practice depends on how you wire it:

• One into two: send your guitar to either of two amps, or drive both at once for a layered sound.
• Two into one: plug two instruments into the two inputs and switch between them into a single amp or pedal chain, or combine them.

KMA describes the ABY as able to "switch or combine your mono input signal using two separate outputs, or switch or combine two" inputs into one¹. The same three modes appear on other makers' ABY boxes, such as Morley's Chrome ABY Switcher with its "Choose A, B or A & B combined" modes³, so the KMA's mode set is the standard arrangement rather than something unusual.

One thing the passive ABY does not have is a phase switch. When you combine two amps, or split and recombine signals, the two paths can arrive out of phase and thin out your sound. KMA's Active models address this with a 180° Phase switch that flips the A channel, "which can prevent signal cancellation and tone issues" when combining or splitting signals⁴⁵. On the passive ABY there is no such control, which is the trade-off for the untouched signal path.

Size, weight and build

The ABY is a small, light box by pedal standards:

At 185 g it is lighter than most overdrive pedals, so it takes little space or weight budget on a board. KMA says the ABY Series as a whole was "created with a focus on durability, reliability, simplicity and hassle-free operation"²¹, and the pedal is made in Berlin, Germany¹.

Power

The ABY runs on a 9 V DC supply with a center negative 2.1mm plug¹, the same standard as the vast majority of guitar pedals, so any typical pedalboard power supply will run it. Current draw is listed at a maximum of 40 mA¹, a light load. This is one point where the passive design differs from some other passive ABY boxes: Premier Guitar's buying guide notes that the Radial BigShot ABY "requires no power (unless you want to power the current version's channel-indicator LEDs)"⁶. The KMA needs power for its relay switching, not just its lights, but the audio path stays passive either way.

The ABY Series: mono, stereo and active versions

The ABY sits in a four-pedal family, and knowing the differences helps you pick the right one.

If you work in stereo, the STEREO ABY covers "stereo operation in both 1 into 2 and 2 into 1 directions"⁷, and KMA's own pitch on the mono pedal is "Don't need stereo? Then the KMA ABY is for you!"⁷. The Active models take a different approach to bypass: they use KMA's Buffered Bypass circuit "to maintain tone on even the lengthiest cable runs"², and add the Phase and Y Direction switches for level matching when combining or splitting signals². They draw more current, at a maximum of 55 mA⁴.

So the choice within the series comes down to two questions: do you need stereo, and do you want a passive path or a buffered one with phase correction? The passive ABY reviewed here is the simplest option, aimed at players who want nothing between their guitar and the amp except a relay¹⁷².

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