The BC307 Cross-Hybrid Line stage Preamplifier
By adjusting the gain of each signal path you can find the combination of signals, which to your ears, sounds the best for any given
recording. Think of it as blending three different shades of blue to get just the right shade. It is important to note that these adjustments
can be made while the music is playing. No two recordings sound the same. Sometimes two songs on the same recording sound
different. Some recordings would sound better on a solid-state system and some would sound better on tubes. The recording
engineer’s taste may be different than yours. You may love the music but it doesn’t sound the way you think it should. This preamp
cannot perform miracles, but it can allow you to improve the sound of a given recording.
Another thing that this preamp does is that it minimizes poor component interaction. We’ve lost track of how many times we have
heard people say that this preamp sounds great but it is a poor match with my amp, or vice versa. If the amp is a little laid back then
perhaps more solid-state in the front end is called for. If the amp is a little aggressive, then turn up the tubes up front. Again, it is not
magic. It cannot make a bad amp sound good, but it can make the marriage between your preamp and amp much happier.
We truly believe that this is a breakthrough component and once again shows that Blue Circle will not be limited by conventional
thinking when it comes to sound reproduction. We will not just keep reinventing the wheel and calling it progress. It is, and always
will be, all about the music.
Almost since the first transistor was used in a piece of audio gear, the debate about what sounds better — solid state or tubes —
has raged on in the audiophile community. Here at Blue Circle we have always adamantly taken the firm and unshakeable position
that “it really depends”. It depends on so many things: the associated gear, the listening environment, the recording you are
listening to, and most importantly, your personal preference. We make wonderful-sounding tube preamps and we make wonderful-
sounding solid-state preamps. The BC307 cross-hybrid line stage preamp, to the best of our knowledge, is the first preamp that
allows you the listener (and really the only one that counts) to tailor the sonic signature of your system to fit the needs of the moment,
and to do it in real time!
This is accomplished by allowing the listener to take the signals from three parallel circuits, and blend them together seamlessly.
A specially designed splitter circuit at the front end of the preamp channels the music signal down three distinct paths. In the stock
version of this preamp there is one path that is pure solid state, one that is 6922 based, and the third is 6SN7 based. Other tubes
and/or combinations are available upon request. Each signal path has its own gain control. A special adder circuit then combines
the three paths and the overall gain is controlled by a master volume control.
Residual noise reference to full rated output: >-110dB or <65uV non weighted
Residual noise reference to full rated output: >-120dB or <22uV within audio band
Hum below 400Hz: >-143dB or <1.5uV
Tracking error tube stage: < +/-0.1dB
Tracking error volume control: <+/-0.038dB
Channel separation: >107.5dB
Frequency response at 15V output: 10Hz to 40K +0.00db, -0.1dB; -1db at 70kHz; -3db at >100kHz
Distortion at 1V output: <0.05 %
Voltage gain: 20.5 dB
Maximum output: 20 Vrms
Volume control range: -95dB to 0db in 62 steps (with high/low gain switch) standard in Shallco attenuators
Input impedance: 50Kohms
Output impedance: <10 ohms
*5 Line level inputs, (5 Bal, 1 SE). Other config available on request.
*2 Pre-amp outputs
*Tube complement: 1-6922, 1-6SN7
*Power requirement: 120Vac 50/60Hz 35Watts - available in 100, 220, 240 Vac
Main chassis: 17.5" (width) x 4.25" (height) x 14.6" (depth)
Power supply 6" (width) x 5.375" (height) x 14.6" (depth)
Main chassis: .35 Lbs.
Power supply: 16 Lbs.