Rane AC-22
Overview
The AC-22 is Rane's stereo two-way active crossover. It uses state-variable Linkwitz-Riley filter alignments - two second-order Butterworth filters in series for each high- and low-pass section. That gives 24dB/octave rolloff slopes and in-phase output from the sections, as Audio-Express (December 2001, p.63) explained in its review. Rane's own advertising ran repeatedly through the late '80s and early '90s. It billed the AC-22 and its three-way sibling the AC-23 as "landmark designs" with 24dB/octave slopes, built-in electronic phase alignment, automatic internal configuration switching, and 41-detent frequency selection (Mix, January 1988, p.67; Studio Sound, March 1989, p.47; Sound and Communication, November 1990, p.16; Recording Engineer, October 1991, p.23). Marketing copy is not a verdict, but the numbers behind it hold up.
Those 41 detents are the main event. The crossover frequency selector uses ALPS pots with 41 discrete settings between 70 and 3.6kHz, so a user can dial in a crossover point precisely instead of hunting around a continuous pot. The delay control moves the low section backward relative to the high output across a 0-2ms range. That is enough to align drivers when physical placement makes true alignment impossible. The unit can also be configured as a mono three-way crossover, and more recent versions added a mono subwoofer switch and output.
The signal path is conservative. RFI, infrasonic, and ultrasonic filters are built in, limiting frequency response from 20Hz to 40kHz. THD and IM distortion are 0.02% at +4dBu - specs provided by Rane and reported by Audio-Express (December 2001, p.63). Input impedance is 20kΩ and output impedance is 100Ω, values that are likely to yield good impedance matches. Gain runs from off to +6dB on both the input and output sections, though Rane recommends against leaning on that gain too heavily.
Two versions exist. The standard AC-22 uses ¼" TRS inputs and ¼" TS outputs, with active balanced or unbalanced inputs and unbalanced outputs. The AC-22B steps up to XLR inputs and outputs, fully active balanced on both ends. Both run from a remote power supply, the RS-1, and both carry UL, CSA, and CE approval with 100/120/230 VAC remote supplies available. The rear panel carries an input and two outputs for each channel plus the external supply connection. The newer variants add the two-channel versus mono-sub configuration switch.
Functionally, the AC-22 lets a user split a stereo signal into high and low bands before amplification rather than after. That reduces intermodulation distortion, since each amplifier sees a narrower frequency spectrum. It also reduces power drain from the amps for the same reason. And it frees the user to optimize amplification per band - solid-state for the low end, tubes for the highs, if that's the flavor someone wants. A DIY speaker builder gets practical wins too: crossover frequency changes are instant, there's no investment in caps, coils, and resistors, each section of each channel gets its own volume adjustment, and one section can be delayed relative to the other.
The AC-22's reputation rests partly on how long it stays in service. One reviewer's unit was ten years old with all switches and pots still working flawlessly. Inside, the circuit is built around Texas Instruments TL072CP dual JFET op-amps for all but the delay sections. They were older parts by the time that review was written, but serviceable. Two zero-cost mods circulate among owners. One is pulling the DC-blocking output electrolytics (C4 and C6 on channel one, C10 and C12 on channel two on later units; C110, C112, C210, and C212 on earlier ones) and jumpering them out. The other is bypassing the infrasonic filter stage by bending pins 5, 6, and 7 of the relevant op-amp out of circuit and running a short wire from pin 1 to pin 7. The infrasonic filter made sense in the vinyl era; with rumble-free sources it's one stage too many. Owners report subtle improvements - more air around instruments, better depth in complex passages, more detail, a generally smoother sound. The same reviewer, though, found the stock AC-22 performed equally well against a DIY tube-based crossover and a homebuilt minimalist Linkwitz-Riley design using Burr-Brown OPA-604 op-amps and polypropylene caps. Op-amp swaps are possible but risky. The circuit can oscillate, and the OPA-604 in particular is known for it.
There are alternatives. Rane introduced an economy line called Mojo in 1996, with the MX 22 and MX 23 as cheaper, simpler options - XLR connections only, stereo controls, no delays. Ashly and Marchand also make affordable active crossovers. At the higher end, DSP-based units with both EQ and crossover functions from Rane, DBX, Yamaha, and BSS cost roughly ten times as much, and time-domain-correcting equalizers from SigTech and TacT push into the thousands.
The AC-22 shows up on the second-hand market for about $150. That's cheap for a piece of professional gear that earned a nomination among 15 classic products - the AC 22/23 crossovers were named among the nominees alongside the Pultec EQ, the UREI LA-4, and the Neve 80 series console.
eBay Listings
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.