Final Model 35

 

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

Spatial Audio Lab Raven

 

Part of the Revelation series, the Raven linestage preamplifier brings Western Electric technology into the 21st Century.

Like the classic WE line drivers of the 1930's, it is transformer coupled throughout, input and output, and fully balanced for minimum distortion. 

The 21st Century enters the picture with ultra low noise power supplies for B+ high voltage and heater supplies, and the state-of-the-art Khozmo volume control, with remote control (standard) and 0.5 dB left-to-right balancing ... on the remote, so you don't need to get up to make precise corrections while you listen.

For maximum flexibility, the preamp has both RCA single-ended and XLR balanced inputs, so it matches a wide variety of phono preamps, DACs, SACD players, and analog tape decks. Similarly, the output is both balanced XLR and single-ended RCA (at the same time). For maximum convenience, there's also a 1/4" headphone jack for high-impedance headphones (300 ohms or greater).

Unlike other vacuum-tube preamps, there's a custom designed wideband output transformer with a 1:4.5 stepdown ratio. As the ratio implies, this multiplies the signal current from the 6SN7 more than four times, making the Raven preamp a tiny power amplifier as much as it is a preamplifier.

The input transformer might seem unnecessary with its 1:1 ratio, but it breaks any possible ground loops between multiple sources and the rest of the system. All of the inputs "float" so there is no electrical connection between the inputs and the sensitive circuits of the Raven. The only connection is the magnetic link between primary and secondary of the transformer. Transformer isolation has been the professional solution in telephone, radio, television, and recording studios since the 1930's, and applies just as well to home audio with multiple sources.

The Raven is a completely different approach than the "Golden Age" circuits of the 1950's and 1960's. It reaches back to the Western Electric of the 1930's and embraces the future with advanced power supplies and modern volume controls.

Specs

Tubes: (x2) 6SN7, (x2) VR150, (x2) 6AX4

Dual-Mono 64-step with Remote Control 4-Source Sequential Selector

Zero feedback, fully balanced design

Frequency Response: 18Hz - 30kHz +/- 0.5dB

Power Draw: 45W

Dimensions: 9” x 18” x 12” 30lbs

XLR: 2 Input (pair) / 1 output (pair)

RCA: 2input (pair) / 1 output (pair)

Headphone Jack: 6.35mm Front Panel