Legend Audio Design Starlet integrated amplifier Measurements

Sidebar 3: Measurements

The Legend Starlet is about as basic an integrated amplifier as you can imagine: three inputs, a selector switch, and a volume control. There's no tape loop, so it wasn't possible to distinguish in the measurements between the active preamplifier section's contribution and that of the power-amp section. The significance of this will become apparent.

Maximum voltage gain into 8 ohms was lower than usual at 38.33dB; a sensible design choice, in my opinion, given that almost all preamps have too much gain for the power amps with which they'll be used. With the volume control set to its 12:00 position, the overall gain was 21dB. The amplifier didn't invert signal polarity and its input impedance was high, at over 200k ohms, though this did vary somewhat with the position of the volume control. Channel separation was adequate at 80dB at 1kHz, worsening to 55dB at 20kHz due to capacitive coupling between the channels, probably across the volume control and its associated connections. Despite the designer's claims, noise levels were only moderate at -66dB wideband, improving to -77.3dB when A-weighted (both figures ref. 1W into 8 ohms and taken with the volume control at its maximum). This was mainly due to hum and dropped as the volume control was turned down. Oddly, the acoustic output from the output transformer was also high in level.

As supplied for the review, the Starlet's source impedance was very high at 3.5 ohms, though this did drop to 2 ohms at 20kHz. As a result, the interaction between the amplifier and a loudspeaker's changing impedance with frequency will be severe, as can be seen from the top trace in fig.1, which clearly reflects the impedance of our standard simulated speaker load. Notice also in this graph the reduction in level each time the load impedance halves, again due to the high source impedance; and the drastic rolloff in the top two audio octaves, which reaches -4dB at 20kHz. The Starlet's reproduction of a 10kHz squarewave (fig.2) correspondingly featured very slow risetimes. It's no surprise that Chip found the amplifier sounded soft.

Fig.1 Legend Starlet, volume control at 12:00, frequency response at (from top to bottom at 20kHz): 2.83V into dummy loudspeaker load, 1W into 8 ohms, and 2W into 4 ohms (2dB/vertical div.).

Fig.2 Legend Starlet, small-signal 10kHz squarewave into 8 ohms.

COMPANY INFO
Legend Audio Design
2430 Fifth Street
Units G & H
Berkeley, CA 94710
(800) 783-7360
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