The Bryston BP 6 C-Series line-level preamplifier, like so
many units these days, is of a simple, basic design with a minimum of extra features.
A note on the measurements of this unit: Both channels
measured very close to each other in all respects with the exception of the volume-control
tracking, which, while better on some other preamps tested, was still quite acceptable.
Chart 1 shows the frequency response with the volume
control set for unity gain for 0.5V input with instrument loading. In this chart, both
channels are shown. The effect of the IHF loading is essentially negligible. The two
channels are tracking within 0.4dB at this point on the volume control. The bandwidth of
this unit (as defined by the -3dB points) is less than 10Hz to about 90kHz. Further,
because the frequency response did not change noticeably with the volume set at maximum
down to -70dB of attenuation, there is no Chart 2 to show these variations. Volume-control
tracking between channels was within about 0.7dB down to -70dB of attenuation.
Chart 3 shows how total harmonic distortion varies with
input level and frequency for both IHF and instrument loading with the volume control set
for unity gain. In this design, there was no difference with instrument or IHF loading, a
desirable attribute of circuit performance.
A spectrum of the distortion and noise residue of a 1kHz
test tone at 0.5V output with IHF loading is plotted in Chart 4. AC-line-hum harmonics
here are relatively low. At this output level, the signal harmonics are so low as not to