Jeff Rowland Design Group Coherence preamplifier & Cadence phono stage
In the past few years Jeff Rowland has revamped his entire product line in an effort to elevate performance to the highest level. For his new preamps, he has reexamined mechanical, thermal, electrical, and interface parameters in order to minimize the impact of vibration, electrical resonances, excess energy-storage effects, and susceptibility to the performance-degrading impact of RFI/EMI. At the same time, the products had to be both buildable and serviceable, if not exactly "affordable," while possessing the Rowland Group's undeniable aesthetic panache.
The Coherence preamplifier and companion Cadence phono stage are the crown jewels of Rowland's current line-up. The massive, two-piece, line-level Coherence and the equally solid Cadence combine brute-force design solutions, cutting-edge finesse, and venerable techniques of old newly revamped, all in a highly modular and flexible layout.
I bought Rowland's original flagship Coherence battery-powered preamp for my reference system not long after its introduction almost four years ago. Had it not been for the distractions of my house-building project, I'd have had this report to you long ago. The silver lining from this delay is that the companion Cadence moving-coil phono stage appeared in the interim, and the Coherence itself underwent refinement, to Series 2 status.
The Coherence and Cadence are housed in three separate enclosures machined from solid billets of 6061 T-6 aluminum. The line-stage chassis are the same height and width as the Cadence phono stage, but the latter is 5" shallower. As a result, the two Coherence main chassis weigh an incredible 88 lbs, while the Cadence is a still hefty 35 lbs. These breathtakingly beautiful enclosures could probably survive a nearfield nuclear explosion.
The Cadence's rear panel is more than 1" thick and provides access to a pair of internal cylindrical step-up transformers nestled within holes routed out of the main body's rear panel. These transformers straddle a small circuit board that rests within its own milled-out socket and contains the active components. The rear panel also features two pairs of input and output XLRs, a 5-pin XLR power-supply connector, and a grounding stud. A single central button and minuscule green LEDs on the front panel select and signal four levels of cartridge loading and configuration of the unit's moving-coil step-up transformers.
The Coherence's main faceplate features a removable center section sporting an attenuator knob, very-high-quality selection buttons and rocker switches, and can either be left in place or used as a standalone, full-function, wired remote control—perhaps mounted on a tripod beside your listening chair. Inside the main chassis are six separate "corrals"—three per channel—milled out from the top to house separate machined aluminum modules containing the I/O transformers and active circuitry.
A connector for the external power supply and seven pairs of high-quality XLR inputs populate the rear panel, along with two pairs of record outputs and two pairs of main outputs—the latter to facilitate system biamping.
The degradation in performance that can occur when connecting single-ended products to (typically) actively balanced gear is not an issue with the Coherence. This is true not only because of the use of transformer coupling and Rowland's high-quality RCA-to-XLR adapters, but because the all-too-common "Pin 1 Problem" has been eliminated: pin 1 of the XLR inputs, which carries the shield current, connects directly to the chassis instead of allowing this unwanted source of noise to penetrate the enclosure and mingle with the audio signal's ground paths—a source of countless headaches and sonic compromises in both the pro and consumer audio worlds. As a result, the chassis acts as an extension of the interconnect shield, as it should. Prospective owners who plan on keeping other components that lack XLR connections, yet who are averse to adapters, can simply have their cables re-terminated with XLRs on one end and RCAs on the other. When having new cables made, just follow Rowland's XLR I/O convention: pin 3 noninverting, pin 2 inverting, which is the opposite of the AES standard.
Inside the Coherence
All I/O connectors in the Coherence are soldered directly to a narrow PC board spanning the inside rear panel. This board also contains high-quality switching relays that allow independent listen and record functions on each input. In addition, since the relays route a given signal to a single pair of Jensen input transformers per channel, only the selected input is connected at any one time. All other inputs might as well not exist electrically, greatly reducing the opportunity for cross-contamination during playback of the selected source.
This rear board also contains one of three Microchip PIC microprocessors used in the Coherence; the other two reside within the power-supply chassis and the front faceplate. Communication among all three chips is via I2C data links and provides individual adjustment of each input for gain, absolute polarity, left-right balance, mono-stereo, and input impedance (selectable between the default setting of 18k ohms and a rarely used 600 ohms). Any of these parameters can be set for each input independent of all others, and all are automatically memorized and recalled when switching from one source to another, eliminating unpleasant surprises when changing from a low-gain phono input to a louder CD source.
An important sonic feature, and a big improvement over Rowland's Consummate preamp, is that within five seconds of engaging any function, all three microprocessors revert to a nonclocking "sleep" mode, thereby eliminating the possibility of digital noise contaminating the music signal. The sleep-mode feature is also carried over to a small, elegantly machined remote display connected to the system with telephone cable. This is not a typical multiplexed-style display, which can generate a lot of interference noise. Instead, you get easy-to-read LEDs showing relative volume level. The last number entered remains displayed at all times (though the control circuit goes to sleep within five seconds of any change).