December 2005
Rogue Audio Tempest II Integrated Amplifier:
Measurements
All integrated-amplifier measurements are
performed independently by BHK Labs. Please click
to learn more about how we test integrated 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 volume
control fully up unless otherwise noted.
- Gain
- Ultralinear: 19.7X, 25.9 dB.
- Triode: 19.0X, 25.6 dB.
- Output noise, 8-ohm load, unbalanced input, 1k-ohm input
termination
- Ultralinear, volume control fully up (worst case): wideband
2.75mV, -60.2dBW; A weighted 0.68mV, -72.4dBW.
- Ultralinear, volume control fully down (CCW): wideband
1.08mV, -68.4dBW; A weighted 0.29mV, -79.8dBW.
- Triode, volume control fully up (worst case): wideband
2.57mV, -60.8dBW; A weighted 0.65 mV, -72.8 dBW.
- Triode, volume control fully down (CCW): wideband 1.02mV,
-68.9dBW; A weighted 0.27 mV, -80.4 dBW.
- AC line current draw at idle: 2.03A.
- Output impedance at 50Hz
- Ultralinear: 0.95 ohms.
- Triode: 0.92 ohms.
- This integrated amplifier does not invert polarity.
Power output with 1kHz test signal
- 8-ohm load at 1% THD (ultralinear): 69W
- 8-ohm load at 1% THD (triode): 41W
- 8-ohm load at 10% THD (ultralinear): 74W
- 8-ohm load at 10% THD (triode): 47W
- 4-ohm load at 1% THD (ultralinear): 18W
- 4-ohm load at 1% THD (triode): 24W
- 4-ohm load at 10% THD (ultralinear): 79W
- 4-ohm load at 10% THD (triode): 49W
General
The Rogue Audio Tempest II is a medium-power stereo
push-pull tube integrated amplifier utilizing one pair of Electro Harmonix KT88EH output
tubes in each channel. This amp has the usual
passive-selector-switch/balance/volume-control arrangement ahead of the power amplifier
proper. Additionally, it has jumpers that can be changed to access directly the power
amplifier input, bypassing the passive front end for external preamp use.
Charts 1A and 1B shows the frequency response of the amp
with varying loads for both ultralinear and triode modes. The output impedance, as judged
by the closeness of spacing between the curves of open-circuit, 8-ohm, and 4-ohm loading
over most of the audio range, is somewhat lower than typical for tube power amplifiers.
The variation with the NHT dummy load in the audio range is about +/-0.6dB. The
ultralinear mode has a bit more high-frequency bandwidth than the triode mode.
Charts 2A and B illustrate how total harmonic distortion
plus noise versus power varies for 1kHz and SMPTE IM test signals and amplifier output
load for the ultralinear and triode modes. Unusually, this design, with its single output
connection for speaker loads, produces about the same power at the point of clipping for
both 4- and 8-ohm loading, albeit at higher distortion prior to clipping. The amplifier
has a 4-ohm output winding that can be connected to the hot output terminal instead of the
8-ohm tap if desired for lower-impedance speaker loads. This behavior would suggest equal
power into 4- or 2-ohm loads with the 4-ohm windings connected to the output terminals.
Total harmonic distortion plus noise as a function of
frequency at several different power levels is plotted in Chart 3 for the ultralinear
mode. Appearance for the triode mode was virtually the same except for the two higher
powers that were 20W and 35W. Amount of rise in distortion at low and high frequencies is
quite pronounced, but not atypical for many tube power amps. Excessive distortion at
higher powers and high frequencies prevented a run at rated power both in ultralinear and
triode modes.
Damping factor versus frequency is shown in Chart 4 and
rolls off at low and high frequencies quite a bit more than other measured tube power
amplifiers. This can be inferred in Chart 1 from the increased spacing between the curves
at low and high frequencies.
A spectrum of the harmonic distortion and noise residue of
a 10W 1kHz test signal is plotted in Chart 5. AC-line harmonics are quite numerous but
reasonably low in magnitude, and intermediation components of line harmonics with signal
harmonics are also reasonably low but visible. The decay of signal harmonics with
frequency is nice and uniform.
Chart 1 - Frequency
Response of Output Voltage as a Function of Output Loading |
1A - Ultralinear
![](chart1a.gif)
Red line: open circuit
Magenta line: 8-ohm load
Blue line: 4-ohm load
Cyan line: NHT dummy-speaker load
1B - Triode
![](chart1b.gif)
Red line: open circuit
Magenta line: 8-ohm load
Blue line: 4-ohm load
Cyan line: NHT dummy-speaker load
Chart 2 - Distortion as a Function
of Power Output and Output Loading |
2A - Ultralinear
![](chart2a.gif)
(line up at 30W 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
2B - Triode
![](chart2b.gif)
(line up at 30W 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
Chart 3 - Distortion
as a Function of Power Output and Frequency |
![](chart3.gif)
8-ohm output loading (UL mode)
Cyan line: 60W
Blue line: 30W
Magenta line: 10W
Red line: 1W
Chart 4 - Damping Factor
as a Function of Frequency |
![](chart4.gif)
Damping factor = output impedance divided into 8
Chart 5 - Distortion and
Noise Spectrum |
![](chart5.gif)
1kHz signal at 10W into a 8-ohm load
|