Tube Power Amp Reviews

The Premier Eleven's input impedance measured 110k ohms. The output impedance was between 0.48 and 0.56 ohms, varying only slightly with changing frequency and load. This is good performance for a tube amplifier, and I would expect the Premier Eleven's performance with varying loudspeaker loads to be more consistent than those of many tube designs. The voltage gain into 8 ohms was 25.7dB. Its S/N ratio measured 84.2dB (L) and 82dB (R), and DC offset was unmeasurably low in both channels.

Fig.1 shows the frequency response of the Premier Eleven at 1W into 8 ohms. The high-frequency peak is most probably due to an output-transformer resonance. While it isn't pretty, it's not high in amplitude, and is unlikely to cause any problem with normal input signals. The response into 4 ohms was the same (not shown), except for a slightly reduced peak amplitude at 80kHz (2.7dB rather than 3dB). Figs.2 and 3 show the squarewave response of the Premier Eleven at 1kHz and 10kHz, respectively. The overshoot and ringing visible in both plots is associated with the resonant peak seen in fig.1. Note, however, the very flat top to the lower-frequency wave shape, confirming the good low-frequency extension seen in fig.1. The Premier Eleven's lowish crosstalk (fig.4) will have an insignificant effect on the amplifier's sound.

Fig.1 Conrad-Johnson Premier Eleven, frequency response at 1W into 8 ohms (right channel dashed, 1dB/vertical div.).

Fig.2 Conrad-Johnson Premier Eleven, 1kHz squarewave at 1W into 8 ohms.

Fig.3 Conrad-Johnson Premier Eleven, 10kHz squarewave at 1W into 8 ohms.

Fig.4 Conrad-Johnson Premier Eleven, crosstalk (from top to bottom at 10kHz): L-R; R-L (10dB/vertical div.).