Exposure 2010S integrated amplifier Measurements

Sidebar 3: Measurements

I preconditioned the Exposure 2010S by running a 1kHz sinewave at 25Wpc into 8 ohms for an hour. After 30 minutes the chassis was very hot, with even the volume control too hot to touch. The amplifier didn't shut down, however. The distortion level was initially 0.035% at this power level, rising slightly at the end of the preconditioning period to 0.048%.

Looking first at the preamp output, this offered a maximum gain of 17.15dB rather than the specified 18dB, sourced from a low 69 ohms impedance. (I note from AD's description that this output uses an op-amp IC, whereas the Exposure's preamp section is passive and therefore can't offer gain, only attenuation.) The preamp output didn't invert absolute polarity, and neither did the main speaker outputs. The amplifier itself offered a maximum gain into 8 ohms of 40.83dB and its input impedance was 18.5k ohms over most of the audioband, dropping slightly to 16k ohms at 20kHz.

The 2010S's output impedance was a moderately high 0.33 ohm at 20Hz and 1kHz, rising slightly to 0.36 ohm at 20kHz. As a result, the interaction between this impedance and that of our simulated loudspeaker resulted in a response variation of ±0.25dB, which might be just audible (fig.1, top solid trace). This graph also shows that, like earlier Exposure designs, the 2010S has a curtailed ultrasonic response (I remember Exposure's John Farlowe once asking me why an amplifier needed to amplify sounds that people couldn't hear), which results in an output down 0.75dB at the top of the audioband. Note the channel imbalance in fig.1; the volume control was set to 12:00 for this set of measurements, and the right channel is 0.25dB louder than the left at this setting.

Fig.1 Exposure 2010S, frequency response at 2.83V into (from top to bottom at 2kHz): simulated loudspeaker load, 8 ohms, 4 ohms, 2 ohms (1dB/vertical div., right channel dashed).

This imbalance decreased to 0.05dB, but now favoring the left channel, with the control set to its maximum position, but increased to 0.6dB with the control at 9:00. However, the amplifier's overall frequency response was identical at all settings of the volume control, something that is becoming rare in high-end amplifier design. The rolloff above the audioband resulted in lengthened risetimes in the Exposure's reproduction of a 10kHz squarewave (fig.2). However, it performed superbly with a 1kHz squarewave (fig.3).

Fig.2 Exposure 2010S, small-signal 10kHz squarewave into 8 ohms.

Fig.3 Exposure 2010S, small-signal 1kHz squarewave into 8 ohms.

Channel separation (not shown) was an adequate 66dB over most of the audioband, decreasing to 63dB at 20kHz. Of more practical concern was the crosstalk between adjacent inputs. While better than 70dB below 300Hz with the undriven input unloaded, the separation decreased to 40dB at 20kHz. Depending on the source component's impedance, the Exposure's owner might hear a wispy trace of whatever is plugged into the adjacent input. It might be a good idea to plug shorting RCA plugs into unused inputs.

The Exposure's signal/noise ratio was good rather than great, at 69dB (unweighted, wideband) ref. 1W into 8 ohms, this improving to 75.7dB when A-weighted. Both figures were taken with the input shorted and the volume control set to its maximum (the latter is unlikely to occur in practical use). However, I did note the presence of some low-level 120Hz hum that I couldn't eliminate by experimenting with the grounding between the amplifier and my Audio Precision test set, as well as some very-low-frequency noise below 5Hz, though this, too, was at a very low level.

Delivering 81W into 8 ohms (19.1dBW) with both channels continuously driven at the 1% THD+noise clipping point (fig.4), the Exposure 2010S exceeded its specified power by 0.35dB. It gave 105W into 4 ohms (17.2dBW), again at 1% THD+N. Into 2 ohms, however, with one channel driven, the amplifier went into protection at 103W (14.1dBW), this indicated by the premature cutoff of the relevant trace in fig.4. Turning the amplifier off, then on, restored normal operation.

Fig.4 Exposure 2010S, distortion (%)vs 1kHz continuous output power into (from bottom to top at 1W): 8, 4, 2 ohms.

At low power levels into 8 ohms, the harmonic distortion remained below 0.05% below 10kHz, and rose slightly above that frequency (fig.5, bottom pair of traces). It more than doubled into 4 and 2 ohms, but was still less than 0.1% below the top audio octave. The presence of some low-level 120Hz hum results in the notch at that frequency in this graph, the hum being out of phase with the signal.

Fig.5 Exposure 2010S, THD+N (%)vs frequency at 4.85V into (from bottom to top): 8, 4, 2 ohms (right channel dashed).

Of more subjective importance than the absolute level of an amplifier's distortion is its spectrum. The waveform of the small-signal THD+N residual (fig.6) indicates a mix of second and third harmonics, though at low frequencies and high powers (fig.7) the second harmonic is highest in level, at –68dB (0.04%). The power-supply components at 120Hz and 240Hz can be seen in this graph, at –72dB (0.025%) and –80dB (0.01%), respectively. When asked to drive an equal mix of 19 and 20kHz tones into 4 ohms just below visible clipping on the oscilloscope screen, the Exposure produced rather more intermodulation components than I expected. The 1kHz difference tone lay at –56dB (0.15%) whether the amplifier was driving 8 or 4 ohms (fig.8).

Fig.6 Exposure 2010S, 1kHz waveform at 2W into 4 ohms (top), 0.055% THD+N; distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.7 Exposure 2010S, spectrum of 50Hz sinewave, DC–1kHz, at 95W into 4 ohms (linear frequency scale).

Fig.8 Exposure 2010S, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 110W peak into 4 ohms (linear frequency scale).

That aside, and taking into account its relatively low price, the Exposure 2010S offers a sensible set of engineering compromises. However, nothing in these measurements indicates why it should sound as good as it does.—John Atkinson

Exposure Electronics
US distributor: Bluebird Music Ltd.
620 Wilson Avenue, Suite 360
Toronto, Ontario M3K 1Z3, Canada
(416) 638-8207