Saturday, June 1, 2024

Spatial Audio Lab Blackbird

 















Although notoriously difficult to drive, the 300B tubes give unmatched low distortion in the most critical location in the whole amplifier.

The trick with the 300B is that it demands a driver with both very low distortion and significant power into a high capacitance load. Most drivers fail at that task, leading to murky and colored sound. With a powerful enough (and linear!) driver, the full beauty and immediacy of the 300B is revealed.

Starting with the most linear tubes for each power range, we choose the most linear possible circuit: fully balanced, and transformer coupled at each stage. No power is wasted in load resistors, as in conventional Golden Age vacuum tube amplifiers. All of the power is made available to the following grids, not just a fraction. The audio signal goes straight from plate to grid, with no detours or side channels.

The signal path is copper, transformers, and vacuum tubes. Nothing else. No coupling caps, no dynamic loads, no phase splitters, no secondary paths, no feedback loops. Just a straight shot from input to output. And it sounds like it; the absence of secondary paths, and various types of signal processing like phase splitters, is immediately evident. You will hear it right away, on any type of music you prefer.

The power amplifiers have a special feature for balanced preamps like the Raven: they take advantage of the balanced, isolated signal and feed it directly to the matched 6SN7 input-tube grids. If a conventional preamp is used, there's a dedicated input transformer that isolates and balances the signal, but using a Raven preamp gives an end-to-end signal chain using fully balanced tubes, with each transformer coupled for maximum signal transfer, with no side chains, feedback, or dynamic loads. Nothing but copper, transformers, and vacuum tubes.


Specs

Input Tubes: (x1) 6SN7

Driver Tubes: (x2) KT88

Output Tubes: (x2) 300B

VR Tubes: (x2) VR105

Zero feedback, fully balanced design

Frequency Response: @2W 18Hz - 30kHz +/- 0.5dB@24W 26Hz - 30kHz +/- 0.5 dB

Power Output: 24W

Dimensions: 10” x 18.25” x 16.25” 53lbs

Inputs: XLR / RCA

3.5mm 12v Input Trigger