Outlaw Audio RR2150 stereo receiver Measurements

Sidebar 3: Measurements

I preconditioned the RR2150 by running it at 41Wpc into 8 ohms (approximately one third the measured clipping power) for one hour. The chassis was very warm at the end of that period, with the area above the internal heatsinks too hot to touch. However, the receiver didn't turn itself off, and the measured THD+noise percentage was the same at the end of 60 minutes as it had been when first turned on.

I have no way of testing a tuner's RF performance, and while the RR2150 has a digital input on a USB jack, I couldn't eliminate a ground loop when I tried driving this input from my PC. However, because the RR2150 has preamp-out and power-amplifier–in jacks, these jumpered in normal use, I could examine the measured performance of both sections individually as well as together. The receiver inverted signal polarity at the speaker terminals; this due to the preamp section. The RR2150's overall voltage gain into 8 ohms measured 42.85dB, this made up of 14.7dB of gain from the preamp and 28.15dB from the power amplifier. The preamp's line-input impedance was a fairly low 15k ohms across most of the audioband, dropping slightly at 20kHz, to 13.4k ohms. The receiver's tonal balance will thus be a touch lightweight with some tube CD players. The preamp section's output impedance was a moderate 880 ohms at high and mid frequencies, rising to 1.1k ohms at 20kHz. The power amplifier section's input impedance was a usefully high 100k ohms at 20Hz and 1kHz, dropping to a still high 53k ohms at 20kHz.

The phono input offered an input impedance of 46k ohms in both MM and MC modes. The gain in MM mode, measured at the preamp output with the volume control at its maximum, was higher than usual at 50dB; the MC mode added another 15dB. Even with the high gain, the MM mode's A-weighted signal/noise ratio, measured at the tape-out jacks, was good, at 66.4dB, though this dropped to 58.5dB with an unweighted wideband measurement. In MC mode, the phono input's S/N ratio was less good, at 48.6dBA.

The response of the phono input showed rather more RIAA error than I'm used to, with a 0.75–1dB trough apparent in the lower midrange (fig.1). The response appears to rise above the audioband, due to the de-emphasis not rolling off the high frequencies as much as specified by the RIAA curve. Phono-stage distortion appeared to be very low, at around 0.02% in the midband, and overload margin, again measured at the tape output, was superb in MM mode, at 30–31dB depending on frequency ref. 1kHz at 5mV input signal. In MC mode, the margin improved by 5dB at all frequencies.

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Fig.1 Outlaw RR2150, RIAA error, MM input measured at preamp outputs (0.5dB/vertical div., right channel dashed).

The RR2150's frequency response through the line input, measured at the speaker terminals, is shown in fig.2. With a low output impedance of 0.1 ohm, there is very little modification of that response into our simulated speaker load (top trace), though the ultrasonic output is curtailed, reaching –3dB at 61kHz. The Outlaw's reproduction of a 10kHz squarewave has somewhat rounded leading edges as a result of this rolloff above the audioband (fig.3). The 1kHz squarewave response (not shown) was essentially perfect. Channel separation in the L–R direction was >80dB below 3kHz, which is good, though 12dB worse in the other direction, not reaching 80dB or better until 400Hz and below.

306OUTFIG02.jpg

Fig.2 Outlaw RR2150, tone, Speaker EQ, and Bass Management controls bypassed, frequency response at 2.83V into (from top to bottom at 2kHz): simulated loudspeaker load, 8, 4, 2 ohms (0.5dB/vertical div., right channel dashed).

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Fig.3 Outlaw RR2150, small-signal 10kHz squarewave into 8 ohms.

Fig.4 reveals that the treble and bass controls offer a sensible range of operation: ±8dB at 20Hz and 2kHz. Fig.5 shows the effect of the front-panel Speaker EQ and rear-panel Bass Management switches. The former applies an approximate 6dB boost centered at 80Hz, 65Hz, or 55Hz to compensate for the limited bass response of bookshelf speakers. The latter high-pass–filters the main outputs to allow use with a subwoofer driven from the RR2150's subwoofer output. The –3dB frequencies are a little higher than the labeling implies: set to "100," the response is down 3dB at 120Hz or –6dB at 90Hz. Similarly, "80" is –3dB at 100Hz and "60" is –3dB at 75Hz. Fortunately, the subwoofer drive signal (bottom traces below 200Hz), which is the sum of the left and right channels, complements these curves.

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Fig.4 Outlaw RR2150, effect of tone controls set at maximum, minimum, and center detented positions (0.5dB/vertical div., right channel dashed).

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Fig.5 Outlaw RR2150 (from top to bottom at 100Hz): effect of Speaker Equalization switch set to 80Hz, 65Hz, 55Hz; effect of Bass Management switch set to 100Hz, 80Hz, 60Hz on main outputs and mono subwoofer output (0.5dB/vertical div., right channel dashed).

The Outlaw RR2150 exceeded its 100Wpc specification by 1dB, delivering no less than 125W into 8 ohms (21dBW) at clipping, defined as 1% THD (fig.6). It gave 190W into 4 ohms (19.8dB), this 0.8dB higher than the specified 160W, and even managed 310W into 2 ohms with one channel driven (18.9dBW). That this $600 receiver managed to survive this high-power testing without blowing fuses or anything breaking is high praise. The RR2150 is a powerhouse!

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Fig.6 Outlaw RR2150, distortion (%)vs 1kHz continuous output power into (from bottom to top at 10W): 8, 4, 2 ohms.

The RR2150 was not the quietest amplifier I have encountered, with a wideband, A-weighted S/N ratio (measured with the input short-circuited and the volume control at its maximum) of 76dB ref. 1W into 8 ohms. A-weighting improved this figure to 83.9dB. The traces in fig.6 imply that the distortion rises from the noise floor above 20W output or so. I therefore measured how the THD+N percentage changed with frequency at 12.75V, equivalent to 20W into 8 ohms. The results are shown in fig.7. The distortion into higher impedances remains below 0.01% in the bass and midrange. Though it rises by a factor of 10 at the top of the audioband, this is to a still good 0.08%, even into the demanding 2 ohm load.

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Fig.7 Outlaw RR2150, THD+N (%)vs frequency at 12.75V into (from bottom to top): 8, 4, 2 ohms (right channel dashed).

The spectrum of the distortion is predominantly low-order harmonics, even into low impedances (fig.8), though some low-level higher harmonics are present (fig.9). The decrease in linearity at high frequencies seen in fig.7 results in some higher-order intermodulation products with an equal mix of 19kHz and 20kHz tones being driven at high levels into 8 ohms (fig.10), though the 1kHz difference product lies at a commendably low –90dB (0.003%). Halving the load to 4 ohms didn't significantly increase the levels of the intermodulation products (fig.11), but sidebands spaced at the ±120Hz power-supply frequency now make an appearance around the spectral components, indicating that the RR2150 is having to work very hard. However, even when I slightly increased the signal level to actually clip the waveform into 4 ohms, the receiver again neither blew its fuses nor broke.

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Fig.8 Outlaw RR2150, 1kHz waveform at 40W into 4 ohms (top), 0.0116% THD+N; distortion and noise waveform with fundamental notched out (bottom, not to scale).

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Fig.9 Outlaw RR2150, spectrum of 50Hz sinewave, DC–1kHz, at 152W into 4 ohms (linear frequency scale).

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Fig.10 Outlaw RR2150, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 115W peak into 8 ohms (linear frequency scale).

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Fig.11 Outlaw RR2150, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 180W peak into 4 ohms (linear frequency scale).

Despite its very affordable price, the Outlaw RR2150 appears to be a rugged little powerhouse. While its measured performance in some areas is okay rather than great—and I was not impressed by the non-flat RIAA response—overall it is sensibly engineered. This receiver easily demonstrates that you don't have to give up an arm and a leg to get true high-end performance from an amplifier, let alone a receiver. I was astonished to discover how much the Outlaw RR2150 could do, and for a bargain-basement price!—John Atkinson

COMPANY INFO
Outlaw Audio
P.O. Box 975
Easton, MA 02334
(866) 688-5292
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