December 2006

Conrad-Johnson Premier 350 Stereo Amplifier: Measurements

All amplifier measurements are performed independently by BHK Labs. Please click to learn more about how we test amplifiers there. All measurement data and graphical information displayed below are the property of SoundStage! and Schneider Publishing Inc. Reproduction in any format is not permitted.

• Measurements were made at 120V AC line voltage with both channels driven.
• This amplifier inverts polarity.
• AC line current draw
  • Plugged in: 0.02A
  • At idle: 1.65A
• Input impedance @ 1kHz: 80k ohms.
• Output impedance at 50Hz: 0.12 ohms.
• Gain (8-ohm load): 54.8X, 34.8dB.
• Output noise, 8-ohm load, 1k-ohm input termination, Lch/Rch:
  • Wideband: 0.295mV, -79.6dBW / 0.465mV, -75.7dBW
  • A weighted: 0.112mV, -88.0dBW / 0.177mV, -84.0dBW

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 400W
• 8-ohm load at 10% THD: 500W
  
  
• 4-ohm load at 1% THD: 640W
• 4-ohm load at 10% THD: 800W

General

The Conrad-Johnson Premier 350 is a high-power solid-state design with wide bandwidth and low output impedance typical of solid-state power amplifiers. It has a complementary MOSFET first stage that provides all the voltage gain of the circuit. The output stage is a complementary bi-polar compound gain of one circuit with MOSFET drivers. No overall signal feedback is used, although DC feedback is employed to help keep the output-offset DC voltage low.

Chart 1 shows the frequency response of the amp with varying loads. As can be seen, the output impedance, as judged by the closeness of spacing between the curves of open-circuit, 8-ohm, and 4-ohm loading, is quite low. The variation with the NHT dummy load (not shown as it won’t show up in the chart) in the audio range is of the order of +/- 0.1dB.

Chart 2 illustrates how total harmonic distortion plus noise vs. power varies for 1kHz and SMPTE IM test signals and amplifier output load. As can be seen, attainable power is greater for the 4-ohm load, as is usual for most power amplifiers.

Total harmonic distortion plus noise as a function of frequency at several different power levels is plotted in Chart 3. Amount of rise in distortion at high frequencies is admirably low in this design.

Damping factor vs. frequency is shown in Chart 4 and is reasonably constant with frequency.

A spectrum of the harmonic distortion and noise residue of a 10W 1kHz test signal is plotted in Chart 5. The magnitude of the AC-line harmonics is typical of many power amplifiers measured. The principal signal harmonics are of odd order with some low-level higher-order components.

Red line: open circuit
Magenta line: 8-ohm load
Blue line: 4-ohm load

(line up at 10W to determine lines)
Top line: 4-ohm SMPTE IM
Second line: 8-ohm SMPTE IM
Third line: 4-ohm THD+N
Bottom line: 8-ohm THD+N

8-ohm output loading
Cyan line: 350W
Blue line: 70W
Magenta line: 10W
Red line: 1W

Damping factor = output impedance divided into 8

1kHz signal at 10W into an 8-ohm load

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