Four envelope generators and four VCAs in ten HP. That is the whole idea of the X-4: if you run a polyphonic or four-voice patch, you normally need a rack row of envelopes and a quad VCA to go with it, and Flame put both into a single narrow panel. It pairs naturally with a quad VCO such as Flame's own 4VOX, but it is just as useful anywhere you need four cheap, fast voltage-controlled amplifiers with envelopes attached.

Each of the four channels has a trigger/gate input, a CV input, a signal input and its own signal output, plus an LED showing envelope activity. A mode switch selects what all four channels do: AR gives attack/release envelopes that follow the gate, AD gives one-shot attack/decay envelopes fired by a trigger, and VCA bypasses the envelope entirely so the channel becomes a plain CV-controlled amplifier. A separate loop switch turns the AD envelope into a gated loop, which makes each channel an LFO-ish repeating shape rather than a one-shot, and a three-position rate switch sets the overall time range from extremely short to long.

The slider on each channel morphs the envelope shape, and that same shape can be driven from the CV input instead, so the envelope contour itself becomes a modulation target. Combined with the loop switch this is more playful than a plain quad envelope suggests: four looping shapes at audio-adjacent rates, each with its own CV over the contour, gets you into territory that has more in common with a modulation source than an amplitude envelope.

One thing to know before buying: the rate, loop and mode switches are global. All four channels share them, so you cannot run channel 1 as an AD one-shot while channel 2 does long AR swells. Each channel also gets a single slider for its shape rather than separate attack and release controls. That is the trade for the size, and if you want per-channel independence you want four separate envelopes and more panel space. What the X-4 does well is exactly what it was designed for: four matched envelopes plus four VCAs, driven from one place, in the width of a small utility module.

Condition: excellent. The silver panel is clean with no rack rash, the screen printing is crisp, all four sliders travel smoothly, the three toggles switch positively and every jack is tight. The rear boards are clean factory work, two boards on standoffs, shown in the photos.

Included: the original ribbon cable and four mounting screws.

Specs: 10HP wide, 40 mm deep. Current draw 60 mA on +12V and 30 mA on -12V. 4x trigger/gate in, 4x CV in, 4x signal in, 4x signal out, all 3.5 mm. Silver aluminium panel. Made by Flame (Fortschritt Musik), Germany.

Shipping from the Netherlands, tracked. Offers welcome.