Jeff Rowland Design Group Synergy line preamplifier 1997 Measurements
Except as noted, all measurements of the Rowland Synergy were made with it AC-powered, set for a low input impedance (as delivered), and with the input sensitivity set for a gain of 12dB. All measurements were made in the full balanced configuration.
The Synergy's output impedance at its line outputs measured 78.6 ohms in the left channel and 79.2 ohms in the right. The input impedance measured 717 ohms in the left channel, 719 ohms in the right. Input and output impedances were not affected significantly by the setting of the level control. The output impedance at the tape output was 198 ohms regardless of source impedance, indicating full active buffering of the tape outputs.
DC offset at the Synergy's outputs was approximately 2mV in the right channel, 0.6mV in the left. The preamp output is pin-3 positive with the front-panel phase switch in its upper position (LED on). (Rowland uses a balanced-polarity convention different from that used by most US high-end manufacturers, which should not be a concern where a phase switch is provided.) With the input sensitivity adjusted for maximum (and the level control at maximum), the voltage gain measured 19.2dB. The S/N Ratio measured 86.6dB (unweighted) over a 22Hz-22kHz bandwidth, 72.6dB (unweighted) from 10Hz to 500kHz, and 88.8dB A-weighted (all ref. 1V) for the line-stage.
The Synergy's frequency response is shown in fig.1. Volume-control tracking was excellent at different settings: within 0.1dB. The crosstalk is shown in fig.2. There is no need to comment on either of these results.
Fig.1 Rowland Synergy, balanced frequency response at 1V output into 100k ohms (right channel dashed, 0.5dB/vertical div.).
Fig.2 Rowland Synergy, crosstalk (from bottom to top at 250Hz): R-L, L-R, balanced (10dB/vertical div.).
As is our usual practice, a high input voltage (in this case, 1.6V) was used for the THD and crosstalk readings to keep noise from dominating the readings. The THD+noise vs frequency plot for the Synergy is shown in fig.3. The distortion levels are vanishingly small across the midband, increasing somewhat at the frequency extremes. The latter is not due to the high input levels used (it was the same when I used an input of 100mV), but in any event the distortion at the frequency extremes is still extremely low. Fig.4 shows how the THD+noise varies with output voltage at 1kHz at three settings of the input sensitivity. The maximum output is nearly the same in all cases.
Fig.3 Rowland Synergy, THD+noise vs frequency at 1.6V and 100mV into 100k ohms (from top to bottom at 100Hz): 100mV, 1.6V (right channel dashed).
Fig.4 Rowland Synergy, distortion (%) vs output voltage into 100k ohms with gain set to (from top to bottom at 10V): 12dB, 6dB, 0dB.
The Synergy's output spectrum with a 50Hz input at a very high output level of 10V is shown in fig.5. While some artifacts are visible above the background, they are at an extremely low level. (The highest is almost 90dB down, or 0.003%.)
Fig.5 Rowland Synergy, spectrum of 50Hz sinewave, DC-1kHz, at 10V into 100k ohms (linear frequency scale). Note that the second and third harmonics are equally high in level at -90dB (0.0003%).
There is little to comment on—or criticize—in the superb test-bench performance of the Rowland Synergy.—Thomas J. Norton