Jeff Rowland Design Group Consummate preamplifier Page 2
Rowland recommends matching the output impedance of the Consummate with the input impedance of a matching Rowland amplifier, which provides for the proper input impedance (300 ohms unbalanced, 600 ohms balanced). If you use an amplifier of another make, however, as I did during these auditions, this is not possible. Accordingly, I set up and used the Consummate with a 300 ohm (balanced) output.
The outboard power supply for the Consummate is enclosed in a chassis which matches that of the preamplifier itself, except for the lack of any front-panel switches. The only control on this unit, the power switch, is located on the rear panel, appropriate as Rowland recommends that the Consummate be left on at all times (though the main outputs, if not the tape outputs, are muted during power-up or during power interruption (footnote 2). Also located on the rear panel are the connectors which feed power to the main preamplifier and, if needed, the outboard phono stages. Internal inspection of this fully regulated power supply reveals dual toroidal transformers, 16 filter capacitors, and 6 transistors and 6 ICs used in the regulation circuitry.
Rowland makes two separate optional outboard phono stages for the Consummate: the Consummate Phono Stage and the Phono Stage II, the latter similar to the phono stage in the Consonance. The former (reviewed here) matches both the preamplifier and the power supply in size and cosmetics, and provides for either single-ended or balanced phono inputs. Balanced operation, which may be accomplished with either an XLR connector or positive and negative RCA inputs, makes use of the fact that a phono cartridge is inherently a "floating" coil, without a ground. In Rowland's input configuration, the positive and negative outputs from the cartridge coil are connected to pins three and two, respectively, of the balanced input; the shield is connected to pin 1 at the preamp input and left floating at the cartridge end. A conventional balanced line would have pin one grounded at both ends, but this is more analogous to the "floating" balanced line from a transformer coil. In any event, this connection is said to reduce ground-induced hum, noise, and distortion. But it also requires special connection cabling, which is where I ran into difficulty. More about that later. Both balanced and unbalanced outputs are also provided.
Internally, the phono stage utilizes discrete, FET, high-current amplifiers with ten discrete, low-impedance power-supply regulators. The critical circuitry is encapsulated into two modules, one for each channel. Build quality is to the same high standard as in the line preamplifier.
Much like its line-level cousin, the Consummate phono stage provides for plenty of adjustment capability. The output impedance may be set at 300 or 600 ohms balanced, 150 or 300 ohms unbalanced. Input impedance (phono cartridge loading) is adjusted by means of either calibrated dials located on the rear panel, or, via external selector switches, internal fixed resistors. I used the former throughout the evaluation. Although the range of this adjustment is usually 80 ohms to 1k ohm, our review sample was set up for a range of 0 to 200 ohms.
For those applications in which a single cartridge is to be used over an extended period (not always the case with reviewers!), Rowland recommends first determining the optimum load value empirically with the calibrated dials, then inserting fixed, high-quality resistors internally and switching to those for long-term use. When 47k ohms is desired for a load, the load-select switch is placed in the fixed position and no internal resistor is fitted.
Rowland believes that the optimum match between phono stage and line preamp is reached when their output and input impedances are matched; the same recommendation they make for between preamp and power amp. However, this requires that the input impedance of the line preamplifier be set to 600 ohms balanced. This is 300 ohms unbalanced, and while the Rowland phono stage is designed to feed such a low impedance without distortion, many other line sources, including CD players, are not. Accordingly, to maintain compatibility with all sources (as most users would require), I set the input impedance of the line stage at its highest value—100k ohms unbalanced, 200k ohms balanced—throughout the auditions. This insures that line sources will remain primarily voltage sources, which is generally their designed function. The lower the current they are required to supply, the better. The factory setting of the line-stage input impedance is 10k ohms (balanced), which would also be fine for most situations.
The physical separation of the line stage, phono stage, and power supply is somewhat cumbersome but minimizes the potential for interaction between them. It also allows them to be located in different locations with optional, longer umbilicals (the furnished umbilicals allow for side-by-side or stacked mounting and not much else). You could easily mount the phono stage near the turntable at the opposite end of the equipment rack from the line stage and power supply. While maneuvering all of these chassis can be something of a problem for a reviewer who reconfigures his or her system often, it's of little significance in a fixed system.
Footnote 2: I found out about the tape outputs by accident. In one comparison, when switching between preamps, I inadvertently plugged the interconnects to the power amplifier into the Consummate's balanced tape-monitor output, which is not affected by the level control. The level was quite loud (though not dangerously so), and when I was unable to control it, I shut down the preamp to investigate. An uncomfortably loud groan issued from the loudspeakers, though fortunately no damage resulted.