Electro-Voice XEQ-2

A single-channel electronic crossover that hides its real flexibility in a plug-in DIP module — change a resistor, change the whole system.

Overview

The XEQ-2 is a single-channel equalized electronic crossover, and the phrase "equalized" is doing more work than it looks like. Beyond splitting the band between low and high drivers, it carries dedicated equalization for Electro-Voice's own TL series low-frequency systems and HR series Constant Directivity horns — the sort of built-in house curve that saves a rack full of external processing when the rest of your system is already EV. The TL equalization is selected with a rotary switch on the front panel; the HR equalization is swapped in via a separate 16-pin DIP module. A third-order subsonic rolloff at 30 Hz is always in the path, which is the kind of quiet protection that keeps woofers alive in rooms where the turntable rumble never quite goes away.

The heart of the thing is the crossover frequency module — a plug-in 16-pin DIP that sets the crossover point. Stock modules ship at 500 Hz and 800 Hz, and the service manual lists a wider menu of resistor modules covering 125 Hz, 500 Hz, 900 Hz, 1.5 kHz, 3.5 kHz, and 7 kHz. Custom frequencies are possible by choosing component values inside the module, and the manual actually publishes the formulas: for the low-pass section RL1 = 16.39M/(f3+6), RL2 = 116.97M/(f3+6), RL3 = 21.03M/(f3+6); for the high-pass, RH1 = 24.32M/f3, RH2 = 9.55M/f3, RH3 = 167.3M/(f3−7.6), with R in ohms and f3 in Hertz. That's a level of documentation most modern crossover manufacturers wouldn't dream of handing out.

The filter itself is a third-order Butterworth, 18 dB/octave, and the manual is candid that this is the "best all around performance for the vast majority of applications" — maximally flat near the crossover, with the low and high sections tuned independently so any combination of slope, overlap, or underlap is possible. By strapping inside the module, the slope can be dropped from 18 dB/octave to 12 or 6. That's not a front-panel switch; it's a bench job with a soldering iron.

A time delay control is provided to electronically delay the low-frequency channel relative to the high-frequency channel, continuously variable from 25 µsec to 2 msec. That's the feature that separates a serious crossover from a toy — aligning a horn's acoustic center to a woofer's is the difference between a system that images and one that smears. The delay is implemented with an allpass filter (U3 and U4), frequency-independent constant time delay up to f = 1/t, with flat frequency response. By paralleling a junction in one XEQ-2 with the identical point in another, the low-frequency outputs can be summed for common (mono) bass applications — a genuinely useful trick for stacked systems.

Specs, as published in the service manual: frequency response 30 Hz–20 kHz, ±0.5 dB, −3 dB at 30 Hz sum of outputs with controls flat. Noise output is −90 dBV maximum re 1 V, 20 kHz noise bandwidth. THD is 0.02% typical, 0.1% max at 20 kHz, +20 dBm. Overall gain is 0 dB into a high-Z load, with a minimum load of 600 ohms and an output source impedance of 47 ohms. Input is balanced or unbalanced — 30k balanced bridging, 15k unbalanced — with input common-mode rejection of 55 dB typical, 60 at 1 kHz. Connectors are 1/4-inch tip-ring-sleeve phone jacks and XLR-3, plus RCA for low-frequency summing. The high-pass filter is −3 dB at 30 Hz, 12 dB/octave. The HF equalization module gives ±4 dB at 10 kHz with Q = 3; a flat module is supplied, others are listed in the manual's table.

Physically it's a 1U rack unit: 1.73 inches tall, 19 inches wide, 4.875 inches deep, 4.74 lbs net. Power requirements are 90–120 V AC, 50–60 Hz, drawing 8 W. A security cover is supplied — the recessed panel and cover suggest it was aimed at installs and rental racks where knobs get bumped, and that's exactly where a crossover like this belongs. Transformer-balanced outputs are a user-installable option via the TRB-1 accessory; a BMK blank module kit is also listed. The power supply is a regulated ±15 V DC design, full-wave rectifier and two three-terminal regulator ICs.

The service documentation is refreshingly honest about one flaw. Early XEQ-2 units may experience intermittent outputs "for no apparent reason," typically caused by low line voltage when the sound system is stressed. The culprit is the anti-thump relay K1 intermittently dropping out at the trough of the AC line. The factory fix: change zener diode D7 from a 15 V 1N5245B to a 12 V 1N5242B, lowering the relay's drop-out threshold. That's the kind of note that only exists because someone, somewhere, had a system cut out mid-show. Buyers of early units should check whether the diode swap has been done.

Servicing is straightforward for anyone comfortable with op-amps. Most of the circuitry is built around commonly available IC operational amplifiers, all stages referenced to ground, so the normal quiescent voltage at any op-amp output is 0 V DC give or take a few millivolts. Any op-amp output sitting at or near a supply rail is suspect. Much of the circuitry is direct-coupled, so the manual advises looking backward toward the input to localize trouble. Service parts were available from the EV factory in Buchanan, Michigan. The manual even explains the part-number convention: a six-digit, one-letter code beginning with 800 rubber-stamped on the parts side of the PCB, with a two-digit one-letter code etched into the foil side as a backup.

For anyone running a bi-amped system with EV TL bass bins or HR horns, the XEQ-2 is the matching brain — the crossover that already knows the EQ curves those drivers want. For everyone else it's a flexible single-channel crossover with a real time-delay control, custom-frequency capability, and documentation that puts most modern gear to shame. It isn't glamorous, and it doesn't pretend to be. The recessed panel, the security cover, the plug-in modules — this is a tool built to live in a rack and be forgotten about until something goes wrong. That's a compliment.

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