Integrated Amp Reviews

I performed a full set of measurements on the Luxman L-509Z using my Audio Precision SYS2722 system. The amplifier is specified as having a maximum output power of 120Wpc into 8 ohms; I preconditioned the L-509Z before the measurements by following the CEA's recommendation, running it at one-eighth that power into 8 ohms for 30 minutes. Following that period, the top panel was warm, at 92.6°F (33.7°C), and the grilles over the internal heatsinks were hotter, at 111.5°F (44.2°C). I performed a complete set of tests using the single-ended line inputs, as they had been used by KM for his auditioning.

Looking first at the L-509Z's unbalanced line inputs, the amplifier preserved absolute polarity at all of its outputs. The volume control operated in accurate 1dB steps in Line Straight mode, and with the volume control set to the maximum, "0," the voltage gain at 1kHz was 43.7dB into 8 ohms from the loudspeaker outputs and from the headphone outputs and 14.67dB from the Preamplifier outputs. These gains were not affected by switching the tone controls, set to do nothing, into the circuit. The single-ended input impedance is specified as 47k ohms. I measured 43.5k ohms at 20Hz, 41.9k ohms at 1kHz, and 34.8k ohms at 20kHz. In Separate mode, which disconnects the amplifier's front-end circuitry from the power amplifier section, the latter's input impedance was 46k ohms at 20Hz and 1kHz, 35.1k ohms at 20kHz.

The Preamplifier output impedance was 680 ohms at all audio frequencies; the headphone output impedance was 80 ohms, again at all audio frequencies. The loudspeaker output impedance, including 6' of spaced-pair speaker cable, was low in the bass and midrange, at 0.1 ohm, rising to 0.14 ohm at the top of the audioband. Consequently, the modulation of the L-509Z's frequency response due to the Ohm's law interaction between this impedance and the impedance of our standard simulated loudspeaker was minimal (fig.1, gray trace). The amplifier's response into resistive loads was flat in the audioband, with its output into 8 ohms (blue and red traces) down by 4dB at 200kHz. This graph was taken in Line Straight mode and with the volume control set to its maximum. Commendably, both the very close channel balance and the overall response were preserved at lower settings of the volume control. The L-509Z accurately reproduced a 10kHz squarewave (fig.2), with no overshoot or ringing.

The audioband response with the tone controls switched on but set to do nothing was still flat, but the output at 200kHz was 6dB lower than in Line Straight mode. Fig.3 shows the effect of the tone controls set to their maximum and minimum positions. The bass and treble controls boosted or cut their passband outputs by 9dB, the midrange control by 8dB.

Channel separation was moderate, at 70dB across the audioband. The wideband, unweighted signal/noise ratio, taken in Line Straight mode with the unbalanced input shorted and the volume control set to its maximum, was a good 72.6dB ref. 2.83V, which is equivalent to 1W into 8 ohms, in both channels. This ratio improved to an even better 83.7dB when the measurement bandwidth was restricted to the audioband and to 86.8dB when A-weighted. Switching on the tone controls set to do nothing decreased the S/N ratios by 12dB. The blue and red traces in fig.4 show the amplifier's low-frequency noisefloor at 1Wpc into 8 ohms in Line Straight mode with the volume control set to its maximum. The level of random noise is low, but odd-order harmonics of the AC supply frequency are present, which will be due to magnetic interference from the power transformer. Reducing the volume by 20dB and increasing the input signal by the same amount so that the output power remains at 1W (green and gray traces) reduced the level of the 60Hz component by the same 20dB and those of the higher-order spuriae by up to 10dB.

Figs.5 and 6, respectively, plot how the THD+noise percentage varies with output power into 8 ohms and 4 ohms with both channels driven. The downward slope below 30Wpc into 8 ohms and 60Wpc into 4 ohms indicates that the distortion lies below the noise up to these powers, but it remains very low until the actual onset of clipping. At our usual definition of clipping, which is when the THD+N reaches 1%, the L-509Z slightly exceeded its specified output powers of 120Wpc into 8 ohms (20.8dBW) and 220Wpc into 4 ohms (20.4dBW). The Luxman clipped at 140Wpc into 8 ohms (21.46dBW) and 225Wpc into 4 ohms (20.5dBW). I didn't test the Luxman's clipping power into 2 ohms, as the amplifier isn't specified as being able to deliver full power into 2 ohms.

Fig.7 shows how the THD+N percentage changed at 12.67V, which is equivalent to 20W into 8 ohms, 40W into 4 ohms, and 80W into 2 ohms. The distortion into 4 ohms (cyan and magenta traces) and 8 ohms (blue and red traces) is very low, rising only a little in the top two octaves, which suggests that the amplifier has a wide open-loop bandwidth. However, into 2 ohms, the distortion in the right channel (gray trace) is higher than that in the left channel (green trace), though it is still low in absolute terms.

The THD+N waveform at 20W into 8 ohms was primarily the second harmonic (fig.8), which will be subjectively innocuous up to much higher levels than those observed in the L-509Z (though some crossover distortion is present; see fig.9). Intermodulation distortion was also extremely low, even into 4 ohms (fig.10).

To examine the performance of the L-509Z's phono input, I connected a wire from one of the Audio Precision's ground terminals to the grounding lug on the Luxman's rear panel. This input preserved absolute polarity in all three modes at all three output types. In MM mode, the input impedance measured an appropriate 44k ohms at 20Hz and 1kHz and 36.3k ohms at 20kHz. In MC High mode, the input impedance was the specified 100 ohms across the audioband. The impedance in MC Low mode is specified as 40 ohms; my measurements were inconsequentially different, at 52 ohms at 20Hz and 42 ohms at higher frequencies. The maximum gain at 1kHz was very high from the loudspeaker outputs: 80.5dB in MM mode, 98.45dB in MC High mode, 106dB in MC Low mode. The maximum gains were all 10dB lower from the headphone outputs and 29dB lower from the Preamplifier outputs.

The phono input's RIAA correction (fig.11) had very small boosts in the midrange and high treble, with a slight imbalance toward the left channel (blue trace). Channel separation at 1kHz was 69dB. The wideband, unweighted S/N ratio, ref. 1kHz at 5mV for the MM mode and 500µV for the two MC modes, was assessed with the inputs shorted to ground and with the volume control set to the maximum. It was a good 71dB in MM mode and 66dB in MC High and MC Low modes. Restricting the measurement bandwidth to 22Hz–22kHz increased the MM ratio by 17dB, the MC High ratio by 4.5dB, and the MC Low ratio by 2.5dB. Inserting an A-weighting filter resulted in ratios of 92.6dB in MM, 74.5dB in MC High, and 73dB in MC Low. The phono input is quiet in all three modes.

To be sure I wasn't prematurely clipping the preamplifier output, I examined the phono input's overload margins with the volume control set to –20dB. The margins were impressively high from 20Hz to 20kHz, at 29dB ref. 1kHz at 5mV (MM), 31.5dB ref. 1kHz at 500µV (MC High), and 24dB ref. 1kHz at 500µV (MC Low). The second and third harmonics were the highest in level in the phono input's distortion signature (fig.12), but at –90dB (0.003%) were inconsequential. The levels of the intermodulation products with an equal mix of 19 and 20kHz tones were similarly low (fig.13).

Overall, Luxman's L-509Z offers excellent measured performance, especially its low-noise, low-distortion, overload-proof phono input.—John Atkinson