ALM Busy Circuits Tangle Quartet (2016–)

Name: ALM Tangle Quartet
Brand: ALM

Four silent, surgical VCAs in 8HP—so clean you’ll swear your patch just got smarter.

Overview

Plug in the Tangle Quartet and the first thing you notice is what's missing. No hiss, no hum, no faint bleed from channel two into three when you're routing delicate control voltages. It uses four THAT 2164-based linear VCAs packed into 8HP. Each one stays out of the way of the signal. It doesn't add character. It strips away noise and crosstalk, so your oscillators, envelopes, and LFOs come through as they are.

No flashy LEDs, no modulation routing matrix, no digital trickery. Just four channels, each with an input, a manual attenuator, a CV input with attenuverter, an individual output, and a shared mix output that sums whatever isn't being patched elsewhere. The CV inputs are normalized to +5V. Leave a CV jack unpatched and the attenuverter defaults to acting as a manual offset, which turns the module into a four-channel passive mixer when you need one. You can use it to shape four drum voices with individual envelopes, blend LFOs for complex modulation warps, or mix audio-rate signals. It's DC-coupled throughout, so it handles control voltages as cleanly as audio - no rolloff, no phase shift, just voltage transfer.

When every signal path is this transparent, you start to hear flaws you never noticed before - noisy oscillators, jittery envelopes, grounding issues that dirtier VCAs masked. That's not a flaw in the Tangle Quartet. If your sources are clean, the results are crisp, dynamic, and present. The panel layout is tight, with knobs and jacks cheek-by-jowl, but owners report that after the first few adjustments it settles into the background.

Specifications

Manufacturer	ALM Busy Circuits
Model	Tangle Quartet
Production Years	2016–
Original Price	£165 / $275
Form Factor	Eurorack
Width	8 HP
Depth	32 mm (including power header)
Power Supply	±12V
Current Draw	+12V: 80 mA, –12V: 80 mA
5V Draw	0 mA
Number of Channels	4
VCA Type	Linear, DC-coupled
VCA IC	THAT 2164
Inputs	4 signal inputs, 4 CV inputs with attenuverters
Outputs	4 individual outputs, 1 mix output
Normalization	CV inputs normalized to +5V
Signal Path	Non-inverting, bleed-free
Reverse Polarity Protection	Yes
LED Indicators	1 per channel (attenuation level)
Manual	Available via ALM website
VCV Rack Module	Available (freeware)
Made In	United Kingdom

Key Features

The 2164 Advantage: Silence as a Feature

The core of the Tangle Quartet is the THAT 2164 VCA IC, a chip long favored in high-end professional audio gear for its near-perfect linearity, ultra-low distortion, and exceptional dynamic range. Many Eurorack VCAs use discrete designs or cheaper ICs that can introduce subtle artifacts. The 2164 doesn't saturate, doesn't color, and doesn't breathe noise into quiet passages. This isn't a VCA for chasing analog warmth or soft clipping. When modulating a filter cutoff with a slow LFO, you won't hear zipper noise. When fading between two oscillators, there's no thump or pop. Because the channels are completely isolated, you can route unrelated CVs - say, an envelope into channel one and a random sample-and-hold into channel two - without crosstalk muddying the results.

DC-Coupled Everywhere: Beyond Audio

Many VCAs are optimized for audio and roll off low frequencies or distort when fed control voltages. The Tangle Quartet is fully DC-coupled from input to output, so it handles 0 Hz with the same precision as 20 kHz. That lets you scale and offset modulation sources. Taper an LFO's output to affect only part of a filter's range, or attenuate a sequencer's voltage before it hits a VCO. You can use it as a four-channel CV mixer, blending modulation sources before they reach a destination. Or patch it as a voltage-controlled offset generator, using one channel to add a controllable bias to a pitch CV. The mix output is handy here: if you only use two channels for active CV processing, the other two can sit idle, their manual attenuators summing into the mix out as a passive CV blender.

Normalization Done Right: From VCA to Mixer in a Patch

Leave a CV jack unpatched, and the associated attenuverter defaults to injecting a steady +5V into the control path, so the manual attenuator becomes a standard level control, like a mixer channel. The module can switch roles on the fly. One patch might use all four channels as envelope-controlled VCAs for a quad drum setup. The next might use it as a four-channel passive mixer for audio or CV, with the mix output summing whatever isn't individually patched. There's no mode switch and no menu diving. The LED on each channel responds to the level of attenuation and works as a crude visual meter. With no CV patched, it glows steadily in proportion to the manual level. With an envelope or LFO driving it, the LED follows the modulation shape. It's not a scope, but it's often enough to tell if your envelope is snappy or sluggish, or if your LFO is bipolar or unipolar.

Historical Context

When the Tangle Quartet launched in 2016, Eurorack was already deep into its expansion phase, and modules were getting more complex, more colorful, and often more expensive. A four-channel VCA with no effects, no digital brains, and no flashy interface could have been dismissed as underwhelming. Instead, it was quietly celebrated. ALM (Alan M. from the UK) stuck to fundamentals while many manufacturers chased novelty. It arrived alongside renewed interest in utility modules - clean mixers, precise attenuators, stable clock dividers - as users began to value signal integrity over spectacle. Competitors like Intellijel's Quad VCA or Mutable Instruments' Veils offered different flavors, some with exponential response, some with additional processing, but none matched the Tangle Quartet's combination of size, silence, and simplicity. It wasn't the cheapest quad VCA on the market, but it was arguably the most transparent.

Collectibility & Value

The Tangle Quartet has never been a "rare" module. ALM has maintained steady production since its release, and it remains available from major Eurorack retailers. In excellent condition, a secondhand unit typically sells for $180 - $220, just below its original $275 MSRP. Mint units with original packaging or early serial numbers might fetch slightly more, but there's no collector's premium. Failures are rare, and when they occur they're usually power-related. The module includes reverse polarity protection, but a misaligned power cable or a faulty distribution bus can still damage the board. Technicians note that the THAT 2164 chips are sturdy, but the dense layout makes repairs tricky. Replacing a damaged IC requires precision and patience. The most common user complaint is ergonomics. The tight spacing between knobs and jacks makes simultaneous adjustments difficult, especially with larger patch cables. Some users report accidentally nudging knobs while plugging nearby modules. It's a trade-off: maximum functionality in minimal space. For skiff builders or anyone tight on HP, that's a fair deal. For those who patch and repatch constantly, it might feel a bit claustrophobic.

Buying used? Check that all four LEDs respond correctly to CV input and that there's no crackling in the audio path when turning the attenuators. Test each channel independently with a steady oscillator and envelope to confirm clean gating and no bleed. Since the module is DC-coupled, you can also verify CV handling by patching a slow LFO into the CV input and measuring the output voltage swing with a multimeter. Any channel that doesn't track linearly is likely damaged. Power draw should be a clean 80mA on both rails; anything higher suggests a short. There's no firmware, no hidden menus, and no delicate components.