Preamplifiers

Mystere ca21 Stereo Tube Preamplifier

ARTICLE INDEX

On the Bench

All distortion measurements were made within an 80 kHz bandwidth.

At 1 kHz and 2 volts output, distortion was less than 0.03%, primarily 2nd order. At 5 volts output, distortion rose to 0.068%, again, primarily 2nd order.

mystere-ca-21-preamp-1-khz-2-volts

mystere-ca-21-preamp-1-khz-5-volts

Using a combination of 19 kHz and 20 kHz test sine waves, the B-A peak at 1 kHz was 65 dB below the fundamentals at 2 volts output, and 58 dB below at 5 volts output.

mystere-ca-21-preamp-19-khz-20-khz-2-volts

mystere-ca-21-preamp-19-khz-20-khz-5-volts

IMD was a very reasonable 0.11% at 2 volts output, rising to 0.27% at 5 volts output.

mystere-ca-21-preamp-imd-2-volts

mystere-ca-21-preamp-imd-5-volts

The THD+N vs. Frequency graph showed a rise beginning at about 2 kHz, but stayed below 0.5% all the way out to 50 kHz.

mystere-ca-21-preamp-thd-plus-n-vs-fr

Distortion vs. Output Voltage illustrates maximum performance at 1 volt output. Clipping (1% THD+N) occurred at 21 volts, which is near the specification of 19 volts.

mystere-ca-21-preamp-thd-plus-n-vs-output

The measured frequency response showed a slight rolloff below 30 Hz, but was only down 2 dB at 200 kHz.

mystere-ca-21-preamp-fr