Pass Labs First Watt B1 Buffer Preamplifier
The B1 Buffer Preamp is described by First Watt as a minimalist line stage for controlling listening levels without editorializing on the source signal. It is a small, lightweight but well built, pressed all-aluminum box featuring a center toggle switch on the faceplate to select between two pair of RCA inputs, and twin attenuation controls for Left and Right channels. On the backside, the unit is powered by a supplied DC power cord; the unit remains powered up when plugged in, as there is no On/Off switch. Along with the two sets of single-ended inputs is a pair of single-ended outputs. That’s it – no muss, no fuss!
The purpose of the B1 Buffer is to address impedance mismatches between a volume control and an amp. Nelson Pass explains in the Owner’s Manual:
“Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control.
This suggests the possibility of using a high quality buffer in conjunction with a volume control. A buffer is still an active circuit using tubes or transistors, but it has no voltage gain – it only interposes itself to make a low impedance into a high impedance, or vice versa.
If you put a buffer in front of a volume control, the control’s low impedance looks like high impedance. If you put a buffer after a volume control, it makes the output impedance much lower. You can put buffers before and after a volume control if you want.
The goal for the First Watt B1 was to make a solid state buffer that was very neutral, with very low distortion and noise, and very wide bandwidth without using negative feedback. It has no voltage gain; its sole purpose is to either increase or lower impedance.”
Download the B1 Manual