March 2004

Threshold Audio S/5000e 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 with 120V AC line voltage.
• Power output and distortion plotted with both channels driven.
• Gain: 24.8x, 27.9dB.
• Output noise, 8-ohm load, unbalanced input, 1k-ohm input termination: wideband 0.260mV, -80.7dBW; A weighted 0.129mV, -86.8dBW.
• Output noise, 8-ohm load, balanced input, 600-ohm input termination: wideband 0.198mV, -83.1dBW; A weighted 0.100mV, -89.0dBW.
• AC line current draw at idle (warmed up): 1.4A.
• Output impedance at 50Hz: 0.0085 ohms.
• This amplifier does not invert polarity.

Power output with 1kHz test signal

• 8-ohm load at 1% THD: 300W
  
  
• 4-ohm load at 1% THD: 520W

General

The Threshold S/5000e is a high-power solid-state design with extremely low output impedance and a relatively high output-stage idling current. The idling current is quite stable with increasing temperature as the amp warms up. Furthermore, and most importantly, the idling current stays stable when the amp is heated up under higher-power conditions.

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 very low. In the case of the S/5000e, this variation with the NHT dummy load would be about a negligible +/-0.01dB. Chart 2 illustrates how total harmonic distortion plus noise versus 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 relatively low -- a desirable characteristic. Damping factor versus frequency is shown in Chart 4. This is one of the lowest output impedance amplifiers tested at BHK labs. A spectrum of the harmonic distortion and noise residue is plotted in Chart 5. As seems to be the case with many amplifiers measured, this one has a rich series of AC line hum harmonics with some sidebands of these harmonics about the nulled fundamental frequency and the signal harmonics.

Magenta line: open circuit
Red line: 8-ohm load
Blue line: 4-ohm load
Cyan line = NHT dummy-speaker load

(line up at 100W 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

4-ohm output loading
Cyan line: 450W
Blue line: 120W
Magenta line: 20W
Red line: 2W

Damping factor = output impedance divided into 8

1kHz signal at 10W into a 4-ohm load

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