Spatial Audio Raven Preamp

I started my career in audio with the invention, patenting, and prototyping of the Shadow Vector quadraphonic decoder, back in 1973. That SQ/stereo decoder was specifically designed to preserve ambient cues and spatial impression, without adding anything like a reverb circuit, or taking anything away from the source material.

There’s a lot of content in a 2-channel recording that is destroyed on playback, or is below the threshold of audibility. This is not the fault of the recording, but the playback system. In general terms, this is low-level information with L/R phase angles between +/- 45 and 180 degrees. A (very good) quadraphonic decoder will route this information to the sides and rear, depending on phase angle, without affecting the frontal image or deforming it. Ideally, random-phase reverberation (from spaced mikes, reverb plate, or good digital reverb) should appear as an evenly weighted sphere around the listener, with no bumps, holes, or hotspots, just as it is in real, physical acoustic spaces. Again, this random-phase information is present on all stereo recordings with even a slight sense of space, because studio professionals consider "dry" vocals intolerable, so some reverb is added on just about everything. And the correct method of presentation is spherical, to match real acoustic spaces.

Unfortunately, 2-speaker playback abbreviates the most realistic spatial presentation, although some speakers preserve a vestige of it. Smooth dispersion patterns, freedom from resonant energy storage in the drivers, and freedom from diffraction artifacts (no sharp cabinet edges) can allow the sound space to leave the confines of the speaker cabinet (as it should in a good loudspeaker). Most listeners never hear this, but it’s still there on the recording, waiting to be heard. (And no, it doesn’t take 11 speakers to preserve spatial information. That’s for special effects in movie theaters.)

For some reason, electronics can also affect the spatial impression. I suspect that many electronics destroy, or alter, the low-level interchannel signals that convey this spatial impression, somewhat akin to MP3 lossy compression discarding "unnecessary" low-level bits. Nothing as violent as that happens in normal electronics, of course, but still, it subjectively sounds like bit reduction, with a loss or "air", spatial realism, and realistic tonality. I am not sure of the mechanism, but high-order nonlinearities, power supply switch-noise grunge, correlated noise, and odd, hard-to-pin-down capacitor colorations (possibly chemical reactions in the dielectric) all seem to play a role in shrinking the sound stage and destroying the ambient impression.

That’s why the Raven and Blackbird minimize energy storage in the signal path. There are no feedback loops, either local or overall. There are no coupling caps, on the input, between stages, or on the output. The balanced circuit presents a nearly constant demand on the power supply, which is further smoothed by the shunt regulator tubes in the preamp. The signal goes in, is fed to a Class A balanced pair of very linear vacuum tubes, and is transformer re-balanced on the way out. No signal recirculation, no phase inverters, no cathode followers, and no secondary side chains (DC servo circuits, dynamic loads, etc.), even at very low levels (which is why it is so quiet).

Listening to my Raven and Don/Lynn's 300b monos, with my Cube Audio Jazzon speakers, is an experience that transports me to another realm... of pure musical enjoyment in an astonishing fashion.  I am not embellishing what I am hearing one bit.

I first connected with Don over 15 years ago when Jim McShane passed him the mantle of upgrading vintage Harmon Kardon amps and preamps, an almost insane task.  He upgraded my C-I, CII, and C-V to astonishing levels.  However, he thought about perfecting the Tubes4Hifi octal-based preamp with a more simplified topology and certainly took that inherently excellent design to masterful levels with his first preamp, his second preamp, and now the Raven.

My tubeoholics friends marvel at the sound of my system with his and Lynn's newest creations in my rack.  As you can see, both of these designers work tirelessly to provide gear to astonish listeners with vivid tonally pure sounds, where the music just seems to float between the speakers and invites me to enjoy my music to the maximum extent possible.  Don for sure listens to his system daily and hourly so he lives with his creations in his own systems and always has an eye towards subtle or significant improvements in his electronics.  I am a big fan and his preamp is simply outstanding.  I'd imagine his 300b monos, while pricey, would fair well against any of uber expensive 300b monos in the market.   Maybe one of the audiophile magazines will seek these units for review.  ;-)

That's why I was pleased to collaborate with Don Sachs, starting a couple of years ago. I already owned his preamp, and I was quite impressed he had decades of experience on the insanely complex Citation I and Citation II preamp and power amps. Those products are not for the faint of heart ... Stu Hegeman was a seriously out-there guy, and a legend back in the Sixties.

Thanks for the kind words!   Working with Lynn has been a pleasure and I have increased my knowledge of tube circuits considerably since I met him..   He got me to consider "going outside the box".  The Raven and Blackbirds are about leaving the box.   Paradigm shifts are always healthy, or at least the consideration of them.  I have built or restored a LOT of tube circuits over the years and nothing I have ever heard or built or restored can touch the Raven and Blackbird sonically.  I think a lot of that is due to what Lynn discussed above about all the very subtle spatial cues that can be lost with lesser electronics and speakers.  I hear things with the Raven and Blackbirds that I have never heard in any stereo before.  Those who have heard them agree.  They don't sound like what you are used to hearing.  They push through boundaries.

As for reviews... we are working on it.  The final production versions of the preamp and amps are just finishing.  These include new cases from a different woodworker.  We didn't want to send out review units that did not look exactly like the final product.  Sonically the gear has been stable for a while, but the final cases had to be sorted out from a reliable supplier who could meet our demand.  That has happened and a set for review will be finished in the next month or so.  We have made arrangements with Positive Feedback to send them a set in the fall, and expect a review by the end of the year.  Of course we hope that owners will chime in as on this thread.   

Lastly, I don't know what shows we may attend, but I am pretty sure there will be a special demo in Portland for the Oregon Triode Society.  Maybe in August or more likely in October.  We will have a large room for two full days with the Raven and Blackbirds, and of course Spatial Audio Lab speakers.   I will be there along with the Spatial team.  So if you are in the Portland area, or perhaps want to make the trek from Seattle, you can hear the preamp and amps paired with top end gear in a good room without all the buzz of an audio show.  When we have a schedule we will let everyone know and hope to see some of you in a relaxed setting where we can all hang out and listen to music!

I expect to be there for the Oregon Triode Society demo as well. Maybe I’ll meet some old friends ... I joined the OTS way back in 1990 or so, at the second meeting.

Way too far to drive all the way from the Denver metro area, so I’ll fly again, but take Business Class this time. My days of flying in Cattle Class are over, can’t handle the crowds or the itsy-bitsy seats the airlines use now. I do miss the Amtrack sleeper service from Denver to Portland ... that was a very nice train ride.

Looking back, I look at the incredible complexity of that Shadow Vector patent (which I invented solo, unlike the three-person CBS team) and how I really jumped in at the deep end of the pool when I joined the hifi biz professionally. Working as a commissioned salesman was such a horrific experience I was strongly motivated to get out of Los Angeles and move to Audionics in Portland, Oregon.

Although I had my differences with Audionics, they did believe in me enough to hire me to build the prototype, which took two years of hard work. That stretch was one of the biggest pushes I’ve done, along with finally completing my Psychology degree a few years later. Speaker design was considerably easier.

Shadow Vector Patent