On the Bench
All measurements were taken with an output voltage of 1 volt. I performed the same measurements with an output voltage of 2 volts and achieved similar results with only slightly higher THD+N measurements. All measurements shown are with the stock volume pot installed. Installation of the Shallco did not make any noticeable changes except where noted below.
When looking at the following measurements, it is interesting to note the accented second-ordered harmonic. It is even more interesting to note the absence of higher order harmonics. This is one of the characteristics that make this tube design so pleasing to listen to. Even-order harmonics tend to sound very natural and add a warmth to the sound, where as odd-order harmonics have a tendency to sound harsh and unnatural.
The first two graphs show THD+N figures of 0.03% for both a 1 kHz and 10 kHz test tone. This is very respectable for a tube-based preamp..
IMD came in at 0.0007% with the standard volume pot installed. With the Shallco installed, IMD dropped to levels below our test equipment capabilities (0.0000%).
The frequency response shows no tendency to roll-off at either end of the audible frequency spectrum and is quite flat from 10 Hz to beyond 70 kHz..
As you can tell, I enjoyed using the BC21.1. The NOS (New Old Stock, which means the tubes are old but unused) tubes allowed me to personalize the sonic characteristics to match my tastes. I personally found the look and feel of the BC21.1 to be very pleasing, and I could live with this preamp in a two-channel system for years to come. I think a number of high-end two-channel manufacturers should spend some R&D budget on building usability into their products rather than adding another oversized cap or shorter signal paths. I am glad to see Blue Circle has taken the initiative of providing a minimal remote option. However, I would love to see a preamp design similar to the BC21.1 with a remote control that has discrete input selection, power, volume, and mute controls. A few high end two-channel manufactures have already started down this path, and I encourage others to follow.
- Sandy Bird -