Solid State Preamp Reviews

The Gryphon Commander's power supply was too heavy for me to lift onto the test bench for the measurements, so I wheeled it into the test lab on a small dolly. I could lift the lighter preamplifier chassis onto the bench, but the power umbilicals weren't long enough to reach the supply on the floor. I therefore placed the preamplifier on top of the supply, separating the two chassis with a stack of 2×4s to provide some separation and to avoid damaging the supply's finish. Still, the proximity of the power supply could disturb the preamplifier's noisefloor.

I used my Audio Precision SYS2722 system to examine the Gryphon preamplifier's measured performance. The Commander preserved absolute polarity (ie, was noninverting) with both balanced and unbalanced inputs and outputs. As set by MF for his review, the maximum gain was 17.5dB from the balanced inputs to the balanced outputs and from the unbalanced inputs to the unbalanced outputs—close to the specified 18dB. Gain from the unbalanced inputs to the balanced outputs was 6dB higher.

The Commander's unbalanced input impedance was lower than the specified 12k ohms, at 7.4k ohms from 20Hz to 20kHz. At 29k ohms, the balanced input impedance was higher than the specified 18k ohms, again from 20Hz to 20kHz. The output impedance is specified as an extremely low 7 ohms. I measured 13 ohms from the balanced outputs and 19 ohms from the unbalanced outputs, both values consistent across the audioband and still very low.

The preamplifier's frequency response into high impedances was flat from 10Hz to 100kHz (fig.1, blue and red traces), with superb channel matching in both balanced and unbalanced modes. The Commander's response into 600 ohms (green and gray traces) was identical. Fig.1 was taken with the Commander's volume control at its maximum setting of "84." The volume control operated in 1dB steps, and both the frequency response and the superb channel matching were preserved at lower settings of the control.

The Gryphon preamplifier's channel separation (not shown) was superb, at >'130dB in both directions below 2kHz, and decreased to a still excellent 114dB at the top of the audioband. From balanced inputs to balanced output, the Commander offered extremely low noise, though power-supply–related spuriae at 60Hz and 180Hz are present in the right channel's output (fig.2, red trace). These are perhaps due to the radiated field from the power supply's transformers, but at –120dB ref. 1V, they are negligible. The wideband, unweighted signal/noise ratio, measured with the unbalanced input shorted to ground but the volume control set to its maximum, was a high 77.5dB ref. 1V in the left channel, 76.5dB in the right. Restricting the measurement bandwidth to the audioband increased the S/N ratio to 89.7db, left, and 87.4dB, right, while switching an A-weighting filter into circuit further improved both ratios to 94dB. Reducing the volume control setting by 20dB slightly reduced the level of noise (fig.2, green and gray traces).

Fig.3 plots the percentage of THD+noise in the Commander's balanced output against the output voltage into 100k ohms with the volume control set to its maximum. Actual distortion lies beneath the noisefloor below an output of 2V but gradually starts to rise above that level. We specify a preamplifier's clipping voltage as being when the THD+N reaches 1%, which occurred with an input signal of 2.6V. The Commander's balanced output level at this THD percentage was 19.14V, much higher than the maximum level the preamplifier will be asked to deliver in typical use. The clipping voltage into the current-hungry 600 ohm load (fig.4) was identical, a tribute to the Gryphon's muscular output stage.

To ensure that the THD+N reading was not dominated by noise, I measured how the Commander's distortion changed with frequency at an output level of 2V. The THD+N percentage was superbly low throughout the audioband into both 100k ohm and 600 ohm loads (fig.5). I examined the spectrum of the distortion at the same output level (fig.6); the only harmonics that can be seen are the second, at –110dB (0.0003%), and the third, at –106dB (0.0005%). Commendably, the level of these harmonics didn't rise into 600 ohms (fig.7). Tested for intermodulation distortion with an equal mix of 19 and 20kHz tones at the same peak voltage level, the second-order difference product at 1kHz lay just above –120dB (0.0001%) in the left channel (fig.8, blue trace) and –130dB (0.00003%) in the right (red). Higher-order products were all below a still negligible –106dB (0.0005%).

With its two chassis weighing 151lb, the Gryphon Commander is the heaviest preamplifier I have encountered. Its measured performance is among the best I have encountered.—John Atkinson