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Digital Do Main - Measured Performance

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Digital Do Main
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Measured Performance
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MEASURED PERFORMANCE

I wondered before testing this amplifier whether its FETs would display the usual wide bandwidth these devices are known for, or whether the designers would avoid working up to radio frequencies. Well, it looks like the latter, because frequency response of the B-1a starts to roll down above 10kHz no less - a very low limit. It  measured -0.3dB at 20kHz – not much of a drop but still unusually low as hi-fi amplifiers go and enough to ensure the B-1a will not sound sharp or bright. Measuring -3dB at 100kHz (our quoted upper limit of 55kHz is at -1dB) the B-1a exhibits a very slow roll off in high frequency output and - thankfully - a sane high frequency limit not out at radio frequencies.

 

Damping factor measured an extraordinarily high 100. This suggests substantial feedback is used, but the amplifier’s special FETs are very high bandwidth devices with good linearity, so it may not be as high as early Japanese V-FET amplifiers. In itself this has no implications for sound quality, but high damping factors (above 30 or thereabouts) can make for dry bass, except when underdamped (boomy) loudspeakers are used, in which case the extra control is beneficial.

 

Distortion levels were low in the midband but rose toward high frequencies, unlike early high feedback FET amplifiers of the 1970s. However, a worst case distortion figure of 0.02% at 1 W into 4 Ohms is low, so harshness will not be evident. The distortion spectrum shows extended harmonics and another analysis, not shown, revealed this was classic crossover distortion. At a low level however, this is not a problem.


The B-1a produces plenty of power, 160 Watts into 8 Ohms and 240 Watts into 4 Ohms. It ran cool on the test bench, in spite of having big heatsinks. Input sensitivity was 1.25V through both unbalanced phono socket inputs and balanced XLR inputs (at full volume). The volume controls did not affect frequency response and performance figures were identical through either input.


The B-1a turns in a good set of performance figures, free of weaknesses. Its peculiarly limited bandwidth and high damping factor suggest there is something different inside. NK


Power 160 Watts

Frequency response 1Hz-55kHz

Separation 97dB

Noise -116dB

Distortion 0.02%

Sensitivity 1.25V

Damping factor 100



DISTORTION, 10kHz, 1W

digital-domain-b-1a-thd1





 

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