Spatial Audio Raven Preamp

Both the preamp and power amp are so symmetric we have to take extra care during assembly to make sure the phase is correct at the output. Multi-color wire comes in handy here.

For that matter, the circuit is so robust it still amplifies with one side non-functional. Distortion is higher, of course, so it’s another thing to be checked during assembly and test. Both phases need to be present and accounted for, polarity correct in every stage, and both channels pair-matched.

Thank you, Don. 

@marantz2270 

No.  The Revelation preamp and the Blackbird amps both preserve phase.  So just hook them up straight.

Is it recommended to reverse polarity at the speaker terminals with the Revelation?

What Lynn said is very audible.  Both the Raven preamp and Blackbird amps use this approach to power supply and balanced circuits.   Once you start listening to circuits built and powered this way it is very hard to go back to conventional approaches because they sound just a bit cloudy or muddy.  It is like a veil being lifted.  The constant merry go round of trying different coupling caps and other things to color the sound in a way you prefer comes to an end.  Instead, once you understand what is going on, you spend a year or two eliminating every bottleneck you can so that the circuit can perform at its best.   What becomes evident is that the circuit and the approach are incredibly transparent.  If you change anything that supports it, you hear it instantly.  Cloud, the main tech at Spatial made the same comment.  You can instantly hear any subtle change you make.  The type of wire becomes very noticeable.  Tube choices are very audible.  Of course you hear these things with other more conventional gear, but not to the extent you do with this circuit and power supply architecture.

Obviously, there are lots of very nice preamps and amps in the world that sound very good.  I used to make some of them myself.  But they don't sound like this.  When you eliminate a lot of the "grunge" that you didn't even know was there, you get a very spacious and airy sound, with incredible detail that you have never quite experienced before.  That is what I hear, and most others who have heard it have made similar comments.  It is not so much about what the circuit sounds like, but rather what the music sounds like when you eliminate a lot of the coloration and distortion that you were never really aware of.  For example, we touched on the idea that there is very subtle spatial information in the signal that is partially obscured by other circuits.  These things are hard to measure, but they can certainly be heard.

I understand that two more preamps have just shipped, so we should get some more reports from owners here fairly soon.  I know it is hard for people because you cannot just go to a dealer and hear the gear, and there are only a few of these in the world, and most are prototype versions.   The production versions are entering the market now, so when people post, the rest of you will get a better impression of how the preamp sounds in a variety of systems to a variety of ears.

I should go into regulators and their sonics a little. Yes, regulators have "a sound". Regulators are amplifiers that feed amplifiers, with the difference the "amplifier" amplifies incoming audio, while a regulator amplifies a DC reference voltage. But it’s an amplifier nonetheless.

Most "linear" type regulators use an internal servo feedback loop to maintain a steady output voltage ... a regulator basically simulates a perfect battery, using feedback to get as close as possible to the ideal. But ... that is an approximation, not the real thing. There are very slight delays responding to a change in current demand, and that is where coloration enter into the sound.

Some audio amplifying circuits have a steady current demand on the supply, and others bounce up and down, following the audio signal. A single-ended audio amplifier, whether tube or transistor, will have a current demand that mirrors the audio. You could put a current sense probe on the supply rails and hear perfectly good music (along with some buzz).

A Class AB amplifier, by contrast, will have quite distorted music on the power supply rails, because it is switching between (B) the upper device, (A) both devices at once, and (B) the lower device. This changes the efficiency of the output stage as the different operating modes change with the music. The switchover between modes can either be hard or soft, depending how the amplifier is biased and how the devices enter the AB cutoff region.

When the load is a Class AB device (like an output stage or an opamp), great demands are placed on the regulator. If it is not a perfect regulator (instantaneous and distortionless), coloration enters the picture. This is why regulators sound different, because a nonlinear load (such as Class AB) then exposes nonlinearities in the regulator.

A balanced Class A amplifier has the great advantage that the load looks pretty much like a resistor at all times, short of heavy clipping. By contrast, the load of a single-ended stage looks like the music it is playing, always varying, while Class AB is quite distorted thanks to a pair of devices switching on and off as the music goes through it. Only well-balanced Class A has a steady draw that doesn’t vary with the music, whether loud or soft, all the way down to zero.

Unfortunately, opamps are limited in not being able to dissipate much heat due to the small package size. Very few opamps are designed to be used with heat sinks. So the only way to keep heat emission low is efficient Class AB output stages, relying on feedback to linearize the crossover region (opamps typically have very high feedback). Higher powered transistor and tube amps also use Class AB to keep heat emission to acceptable levels, at the expense of higher distortion in the Class AB transition region.

The nonlinear load challenges the regulator design, and regulators for the output stage of transistor and tube power amps can be as large and heavy as the output stage they are powering. In effect, one amplifier driving another. This is why it is very rare for medium or high power transistor or tube amps to have regulated output stages. Usually they have a simple lowpass filter with no regulation, saving a great deal of cost and weight compared to the regulated alternative. With no regulation, the sound will always change, depending on the incoming voltage fluctuations, the AC waveshape, and the noise riding on top of the AC power.

The rigorous solution is fully balanced Class A operation for every stage of amplification, not just one or two, and low-noise precision regulators for each of those stages. This keeps the workload of each regulator to a minimum, and the current draw on each regulator is constant regardless of audio signal. It also maximizes isolation between the AC power line and the incoming audio signal.

The Raven also uses an isolation and phase splitting transformer for unbalanced RCA inputs, while balanced signals go straight to the 6SN7 tube grids. Regardless of the incoming signal, whether balanced or unbalanced, the stepped-resistor volume control and internal electronics are always in Class A balanced mode.

I’ve been using damper diodes (from old TVs) since 1997. I’m frankly surprised why people are still using the audiophile favorites. Damper diodes have (much) quieter switching, have substantially higher peak current, and sound noticeably better. The only downside is they consume a lot of heater current and require 6.3V heaters. The majority of damper diodes also use unusual sockets, so they are not pin-interchangeable with the standard types.

The parameter I care most about is smoothness of switching. This is hard to get right, with most vacuum diodes having sort of a Class AB switching region. This can be examined by using a scope probe with a 100X internal attenuator and a safety rating of 1kV or better, connected to the secondary of the power transformer. Voltages are very high, so great caution should be exercised while making the measurements.

The worst diodes have a rough transition between 0 and 50 volts, with holes chewed out of the waveform (generic solid-state bridge). The OK quality ones are fairly smooth but the zero crossing region (measured at the power transformer secondary with special probes) is quite obvious, with small variations between the usual audiophile favorites (which is where the famous tone color comes from). The best diodes almost look like Class A triode, with very smooth transitions that are complementary. Only damper diodes do that. They also have peak current capability that is 2X to 5X higher than any standard 5V heater diode.

With skill, snubber circuits tuned to the transformer, HEXFREDs and high-voltage Schottky’s can approach damper diodes in quietness, which makes them useful for power amps that have to handle a lot of power.

Why the obsession with switching noise? It’s much easier to reduce noise at the source then attempt to filter it later. The harmonics from the 100/120 Hz switch noise sneaks past regulators, magnetically induces noise in nearby circuits, and radiates back out the power cable. Better to minimize it right at the source, which is a function of the transfer curve as the diode is switched on and off.

At Spatial, we use a belt-and-suspenders approach to power supply design. We select the quietest diodes for the application, use CLC filtering as a pre-filter, then apply that to a precision regulator with 130 dB of noise rejection. The regulated output is then applied to a balanced audio circuit with another 35 dB of noise rejection (due to inherent balance). The servo circuit in the regulator has very little to do since the current draw from the audio circuit is very nearly constant, thanks again to the inherent balance of the audio circuit.

@charliee

The damper diodes are extremely tough, they are very quiet, and we are running them VERY conservatively. They have tons of headroom and will last a long time. That, and you can buy lots of them for very little money. So a customer can buy a couple of sets for the price of one decent quality conventional rectifier, and FAR less than an NOS Mullard GZ34, or even new production high quality 5U4 or 274b types. Truth is the damper diodes sound better anyway. Also, in this preamp you can use the 6W4 and there tons of those out there as well for under $10 per tube.

My previous preamp sounded best with the 6BY5, a dual damper diode. So that was my first experience listening to them a lot in a preamp circuit.

@donsachs 

I'm looking to purchase the pre within the near future, it seems to be the top option in my price range. Just looking at the Raven on the Spatial site I saw that it uses two 6AX4 rectifiers. If you don't mind me asking, why that rectifier and not one of the units that are popular with tube rollers, such as the 5U4G, 274B, or the GZ34?Would they not work with the design, or too expensive, etc?  Thanks.

@jc4659   Well, it's ok to post an initial impression:)  But then please follow up with the 20+ hour report.  You get most of it within 20-30 hours, but there are subtle improvements out to 100 or so as the big cathode bypass caps run in.  Most of it is there by 20-30 or so though...   Enjoy.  Hope it works well in your system.

Heard from Spatial that my Raven should ship tomorrow.  I am very excited to hear this preamp in my system.  I will try to refrain from posting initial impressions until adequate burn-in (20+ hours).

I have word from Spatial that the next batch of 5 Ravens is in production, so those folks awaiting builds should have them pretty soon.  Then some of you can post your impressions here!  It will be good to know how people like the preamps in a variety of systems.

Indeed the signal path on both the preamp and amp is very simple.  That said, the power supplies supporting it are rather complex and they are kept well away from it.  Also, the preamp output transformer and amplifier interstage transformers took over a year of prototyping to get right.  So the circuits are "deceptively" simple, but there is a lot supporting them, and as Lynn stated, these circuits are kept well away from the signal path, both electrically and physically.

Also, if you spend time reading this thread and the very long 300b lovers thread, you will see that the "deceptively simple" circuits are also cleverly designed to eliminate distortion at its source as well.

Part of the reason for the sonics (aside from the circuit) is the physical simplicity of the preamp. No circuit board is needed because there really isn’t that much to the audio signal path. Input selector -> balanced switched-resistor volume control -> balanced 6SN7 vacuum tube -> output transformer. That’s it.

There are no coupling caps, no multi-transistor current sources with Zener-diode references, no muting relays with time-delay logic, and no DC-balance servo circuits ... so there’s no need for circuit boards to contain all these secondary functions. Just very short point-to-point wiring.

The same is true of the Blackbird power amp, as well as the Raven. The audio path is surprisingly simple.

Wonderful! Have my eye on the preamp! 

Let's just say that before building my own tube creations I restored probably 300-400 pieces of vintage tube gear, including about 75-80 citation II amps, over 40 citation I preamps, and many Scotts, Fishers, Sherwoods, Macs, Marantz 8b, etc... I saw what were clearly high quality build practices, and cheap ones too.  I always appreciated the gear that was easy to work on, and hated designs that were difficult to rebuild.   So everything we build is designed so that it is easy to work on should anything ever go wrong.  It is designed so that things are never run anywhere "near the ragged edge".   Tubes are in class A, but still conservatively run and should have long lives.  I want the customer to enjoy the gear for years, and should there ever be a problem, I want the tech to easily be able to swap out a part and have it running again. 

I remember working on Marshall guitar amps for musician friends.   They have a dozen little pcbs, tied together with jumpers cables that all have the same terminals, so that you have to mark each board and cable so you know how to put it together again.  The problem would always be on the bottom board!   So we avoid construction like that.  This gear is a bit complex, but very modular, the layout is neat and clean, and it is designed to be trouble-free.  For example, all AC is on one side of an internal shielding bracket, and all signal path on the other in both preamp and amps.  Star grounding, with strong attention paid to current loops.  No hum!

Impressive build and handling of the important details. Thank you for such a detailed answer. I’m very impressed with the quality and design of these products as well as the transparency and comprehensiveness of the responses. You and Larry are to be commended. Thank you.

@grannyring The preamp, and the matching amps are point to point wired, yes. The tube sockets are all mounted directly to the top panel in both pieces. The only pcbs are there to hold large film capacitors to facilitate mounting them securely. The regulated power supplies, both high voltage and tube filament, are built on small pcbs, which are point to point wired to the rest of the components. Again, all signal path wiring is point to point with very high quality wire. The power supply wiring is all teflon insulated mil spec copper. Signal path is all copper as well, but there is no teflon insulation in the signal path. There are NO electrolytic capacitors except in the regulated DC filament supplies. The entire high voltage B+ supplies in both preamp and amps are built wtih all film capactitors, all resistors are wire wound.

All parts are chosen so that they are run very conservatively. No part exceeds 60% or so of its voltage or current or temperature rating. For example, the DC filament supplies can deliver 3A of current and in the preamp they provide 1.2A to the pair of 6SN7 tubes. Resistors are run at no more than about half of their power rating anywhere in the circuits. The preamp and amps are designed to last a long time and to survive the odd tube failure without damage to the unit.   You can put your hand on the power transformer of the preamp or amplifiers after hours of use. Even though both circuits are class A, they run at reasonable temperatures and do not stress their transformers at all.

This question may have been covered, but I have not seen it.  Is the preamp part to part wired? Combo of circuit boards and PTP wiring? Are the tube sockets mounted to circuit boards? 

Most interesting product and thread.  
 

As Don mentioned, avoid the thick and crazy-expensive audiophile cables. You have to remember most audiophiles have noticeably colored transistor gear, and use aftermarket products like power conditioners and $5000+ cables to minimize glare, grain, and excessive HF output in their systems. The better approach is using low-coloration electronics and loudspeakers with a smooth response, especially above 2 kHz.

The key spec in any cable, much more important than any other, is capacitance per foot (or meter). Capacitance should be well under 100 pF/foot, preferably much, much less. Inductance *does not* matter unless you are running an AM transmitter (those are RF cables). Inductance does not load down the preamp, but capacitance does, occasionally causing transient instability in a preamp with high feedback. The Raven has zero feedback, but solid-state preamps typically have very high amounts of feedback (40 dB or more), resulting in load sensitivity to the preamp/amplifier interconnect.

The quality of the insulator (dielectric) in the cable also affects the sound, and Teflon is not necessarily the best. It’s the first choice for aerospace applications, and has exceptional DF and DF measurements, but in my experience, may not the best for audio. Various types of plastic all have their own colorations, and the process of fabricating the cable applies mechanical stress to the plastic, which changes its dielectric properties. The more complex the construction, the more complex the coloration, and the longer it takes to settle down (possibly never). Most of all, DO NOT TRUST the reviews you see in magazines or on the Internet.

Thank you for the advice Don and Lynn. The Paul anticables do sound enticing.

You can make very nice xlr runs out of Duelund tinned stranded, but it is spendy these days and you are talking long runs.   I use Paul's anticables in my system, but they are only 3-4 ft runs.  If you are running 8-10 ft over to a powered speaker that could get expensive as well.  Belden wire is quite cost effective usually if you hunt around for sources.  There are a million pro audio cables in the world, and that is essentially what you are doing.  I would start there and see how it sounds.  Like Lynn said, avoid super thick "audiophile" cables.

Yeah, stay away from the garden hoses and faux snakes, no matter what the reviewer says, or in what magazine. Simple is good, less capacitance per foot is better. The studios don’t use garden hoses or faux snakes, why should you?

Many of the reviews of $5000 cables are using them as system-wide tone controls. Wrong approach. Cables just need to get out of the way, nothing more. If EQ belongs anywhere, it's in the speaker crossover, where it can do the most good.

Thanks for the information, Lynn, especially on the cable recommendations. I can't wait to hook up the preamp. 

I heard the powered ATC monitors at the last Rocky Mountain Audio Festival, and they were some of the best speakers at the show. The ATC midrange driver, in particular, is a legend in the speaker industry, and ATC did a really good job with the active crossover and the internal power amps.

The Raven can easily power 20 to 50 feet of balanced cable with its 4.5:1 step-down output transformer, so it should be an excellent match for the ATC monitors. Studio-grade Mogami or Belden XLR cables should be quite good, but there’s Cardas, Dueland, or Anticables if you want to spend more. I would stay away from high-capacitance cables that look like garden hoses. Capacitance is not your friend when it comes to long cable runs.

I am looking forward to hooking up the Raven to my Odyssey Audio Khartago monoblocks. The Model 2 sounds great with them as it is. However, I do plan on getting the active ATC SCM 40A v2 speakers as they have the XLR connection.

Thanks @donsachs  I appreciate the response. Sounds like a good match for me. 

@fthompson251 Lynn and I designed the Raven and I have lived with all the prototypes and final version for many months and it has all the tube things you like, but is far better than any tube preamp I have ever built or heard.  It throws a sound cloud with very detailed pinpoint imaging, provided the rest of the system can do that.  Plus, it will drive the XLR inputs on your Coda amp, so if your source is balanced, then you will have a completely balanced system.  Of course the Raven will also handle rca inputs and outputs, but there advantages to a fully balanced system from source through the power amp output.  So I hope a few folks with Ravens will give their impressions on this thread.  There are a couple of prototype Ravens floating around and those folks have chimed in above I think.  There is also a Raven thread on the spatial audio lab audio circle.  I know that Spatial will be building the next 5 Ravens within 7-10 days, so hopefully a couple of the new owners will also chime in and you will have a basis for a decision based on an opinion other than mine, since I am incredibly biased:)

Hi remember me, I started this thread. 😁 Anyway, I finally got my Coda s5.5 amp introduced into my system. (In user systems) I replaced my VAC Renaissance 70/70 amp and VAC Cla1Mk III preamp. I use the Legacy Wavelet II as the preamp/crossover/DSP room correction now. With very little time on the rig it sounds very good but I think I would like to add a little "Tube magic" back into the system's midrange and soundstage if possible. So the question is for those that now have the Raven, does the preamp have that characteristic at all? I remember before when I had to run my Focus XD's full range the VAC Preamp added just the right amount of tube flavor to satisfy, so looking for a bit of that. I don't see any reviews about the preamp in this thread so far, just checking.  Thank you!

BTW, I am saving for the Raven, but had a few set backs that detracted from my savings for it, but back on track now.

I am hoping to receive word that my Raven will be shipping by the end of this week.  I plan to post my experiences here after at least 20 hours of burn-in.

The Raven design is stabilized and they are in production at Spatial Audio Labs in Salt Lake City. Don Sachs lives in British Columbia in Canada, I live on the outskirts of Denver in Colorado, and we both communicate with Spatial on a regular basis.

I use loudspeakers that are designed to be close to room corners, but the room in our new home could not accommodate that setup. While losing the corners decreased bass and the overall energy, I did gain some detail as a benefit. After doing a lot of research, I wound up adding, in my case, custom open baffle subs even though my loudspeakers go down to 30Hz as-is. It’s an unconventional setup as the subs are in-between my loudspeakers and my centered audio rack. However, this not only solved my bass/energy issue due to the loss of corners, but the subs strengthened the system’s foundation, and now it has more detail, sounds bigger, and retains the relaxed sound that I love.

I am also very interested in the Raven preamplifier.

Kenny 

There is a whole subculture of modding the classic Klipsch products ... Cornwall (probably the easiest to tame), La Scala, Belle Klipsch, and of course the Klipschorn. Look up "Klipsch Forums" and off you go. Classic Klipsch are famed for dynamics but the frequency response can be sort of uneven in the 1950’s manner.

Aside from response irregularities, the quality of the factory crossover parts is kind of marginal. But there are at least two different vendors selling premade souped-up crossovers for each of the classic Klipsch models ... no soldering needed.

The KHorn definitely requires corner placement in order for much bass below 60 Hz ... the corner of the room completes the horn mouth, expanding it several times. Some folks actually use false corners, which work fine, provided the false wall is reasonably rigid and doesn’t vibrate.

If the Khorns are basically new models from Klipsch, I wouldn't dig into the crossover because, yes, you will void your warranty.   Just enjoy them.  I modded Cornwall IV and they had cheap caps in them and very cheapo sand resistors, including one in series with the midrange horn.  Changing to good caps and path audio resistor on the horn made the speaker much better than stock.  I sold them to a guy who loved them, so the warranty wasn't an issue for me or him.   If the khorn has similar caps and resistors in it as compared to the Cornwall IV, then you can definitely get better sound, but at this point, get your system set up and just enjoy it.  You may go in a different direction on speakers eventually, who knows.

@donsachs I have gone about this room and system a bit bass ackwards. The walls do have resilient channels and quiet board on top. The room isn’t a 100% listening space as I’m a retired (but still doing some work) photographer. It’s a multi purpose room. Currently a small set is up blocking the left speaker a bit and the tunes still sound good. Big imaging not so much.

The Klipschorn’s AK6 sound good smack dab in the middle of the room as well as the far end where I have an editing station. If space would have allowed speakers that were several feet out in the room I would have not used the Khorns AK6es. I have a 9x12 north window that makes for a great natural light source. A daylight studio is tops. The (now translucently shaded) small high windows make it so the room has two light sources as a room with just one light source is off-putting. (A PATTERN LANGUAGE Towns, Buildings, Construction By Christopher Alexander, Sara Ishikawa and Murray Silverstein is a great book)

This is to scribe I know my light stuff but maybe not sound stuff as much.

To divert. Many years ago I had a big party and rented a friends brother’s Khorns. When it was time to take them back his wife told me I could buy them. I said, ‘I could not afford them”. She said, “yes you can”. She was very pissed off at them in their small living room. I paid scant little for them. He got back as his wife with voluminous electro static speakers that went to the ceiling. They are still married. I sold the Khorns to a client and over thirty years later they still are in use.

Diversion #2. Close to fifty years ago my parents had a marital separation and my mom was righteously mad at my father. He moved out and she gave away his beloved chest high Tannoy speakers, MC 275, records and turntable. They reconciled but no more big rig came back. I asked Mom why she didn’t give them to me and she said she never thought of that.

This is the background stuff that forms us. Dad was into stereo. I have been since I can remember ( but with out funds to indulge as I now do until a few years ago ) and now my grown sons are too.

The “plan” was to do sound treatments and then get serious about amplification and a pre. I have been a 300B lurker for years and the Raven/Blackbird’s are on order after an unexpected windfall and well you know the rest.

I never planed to use the Lumin AMP long term but it’s what I had (snarfed up on Agon) with the Khorns but it’s a lot more than Aok as a place holder.

Should I better the cross overs in the AK6’s and if so with what? It took three of us to get the Khons up on special sound dampening blocks and as they still smell new. (a lady bought them and retuned as she didn’t like the color!!!!) Will I void the warranty if different cross overs are put in?

Room treatments should make a considerable difference in quashing the bit of echo. Next week I’m off to find a big rug remnant and get it bound and will order 24-30 panels. VERY dynamic requires that too.

Quote the Raven

No one here can love or understand me
Oh what hard luck stories they all hand me
Make my bed and light the light, I’ll arrive late tonight
Blackbird, Hi. Hi. Helllooooowwww.

@wsrrsw Fasten your seatbelt, that will be a VERY dynamic system.   Have you rebuilt the crossovers on the Khorns?  If not, there is improvement to be gained there.   The Khorns are a wee bit bass shy below 50 Hz or so, but the amps will give you everything those woofers are capable of.

Let us know when you have a few hours on it all.

@donsachs Youbetcha. Initially will use a Lumin X1 w/ Khorns. Was going to treat room before this (major) Amp/pre upgrade but a windfall happened and rather than a spiffy wardrobe (who me?), tango lessons or going to the Tour de France this was the best option. Room treatment on tap. Excited!!! Whee Ha, Daddyoh. 

@wsrrsw Yes, I heard someone bought the preamp in the last of the old style cases, and one of the last two pairs of amps in the old style cases.   The amps are electrically the same and so is the preamp.  Please report back once you have them up and running and have 10-20 hours on them.  Please let us know what other gear  you are using with them.

Thanks!

Hope you enjoy it!

Don Sachs, Spatial Audio, and I are right at the beginning of the production curve, with the preamps a little ahead of the Blackbird power amps. The designs are finalized, stable, and several steps more advanced than what was shown at the Seattle Audio Festival last June.

Both are quite different than other tube audio products that mostly date from late 1950's designs. They are a combination of Bell System/Western Electric line amplifiers and 21st Century computer-designed transformers and power supplies.

After years of pondering next move....Called and they had one left. Got it and AMPs too! Kid in a candy shop. 

I want to revisit what Lynn said about subtle content that is present in two channel recordings.  The content that gives the ethereal sense of space, and the very subtle reverb that is present from recording techniques or actually added by the producer.  I have owned really good stereos for years, both rebuilt vintage-based, and my own creations.   What the Raven (Revelation) preamp and the matching Blackbird amps do is to present this information.  It is not masked as in most systems, including some very good ones I have owned, and some very expensive ones I have heard at audio shows.  I am listening to the final versions of the Raven and Blackbird amps, and I hear these things that I have never heard before in recordings I am very familiar with.  It adds a whole new level of enjoyment and has been discussed, you can hear the intent of the musicians and the producer or recording engineer, and the room if the recording is from a live performance.   

The shoebox mono prototype amps mentioned by @sjsfiveo ​​​and ​@whitestix will give a portion of this effect and are very good.  The final version of the amps have it in spades.  We have improved both the preamp and amps just a wee bit since the Dallas show and I am looking forward to the next demo of the Revelation series so that others can hear what I get to enjoy in my living room daily.   I completely understand that a $19,995 pair of amps is outside the budget of many folks, but I do thoroughly enjoy playing them for people so that they can hear what is possible and what we have been up to.   Most people (myself included up to two years ago) have never heard this sort of presentation.  From a design standpoint, I understand exactly why all of our choices work well with this circuit idea, and why the system sounds as it does.  But hearing it is quite astounding to me.  It just vanishes and leaves the music hanging space for you to enjoy.

@sjsfiveo Yes, price has very little relationship to sound quality beyond a certain point.  One walk through an audio show will make that abundantly clear.  The Revelation series project was about designing the best sounding preamp and amps that we could using ideas that Lynn has been working on for decades, that have their basis in wonderful circuits and approaches developed a LONG time ago.  We implemented those ideas with modern power supply, filament supply, transformer, and attenuator technology that I had been using for a number of years prior to that.  The idea was to build the best sounding preamp and amps we could and then price them based on the build cost and required profit margin for the manufacturer to stay in business, while paying real technicians in Utah, real living wages.  You really cannot build gear of this quality on a shoe string budget.  That said, the gear does not cost six figures, nor does it have to!   

I have Don's 300b Shoebox Mono's and preproduction Raven and the combination is stellar. The music is authentic and rich and musical with the ability to listen to hours and hours without feeling tired or fatigued. It has everything I've always wanted in my system without overreaching. It has all the detail you could ask for without being analytical, clean but not to the point of being sterile, full without heaviness. I'm so happy with the sound that most if not all other systems I listen to anymore just don't do it for me even many multi 6 figure systems one of them being a $600,000 system.

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

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!

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.

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.  ;-)

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).

@donsachs You touched upon the primary reason I am moving back to tubes from solid state. No question there are very competent solid state electronics that can create a 3D soundstage.  My Ayre K-1xe does a better job at this than the Ayre K-5xeMP preamp, for example.  I have been able to attain a wide soundstage that extends beyond the speakers and has good depth and height on certain recordings.  What the Raven seems to deliver as described by yourself and other users is what I've been missing.  The wait is killing me.

@jc4659 I can assure you the preamp sounds believable.  The sound stage is entirely dependent on the recording.   On most every recording except mono ones, the image in my system using the Raven and the matching Blackbird amps will always extend several feet outside the speaker boundary with good depth.  Smaller sounds are physically smaller and things that are farther away are rendered that way.  On other recordings, the music will extend towards you and partially wrap around to the sides.  I use the analogy of omnimax theater for the ears.  Again, it is totally dependent on the recording.  I will get in trouble for saying this, but I will say it anyway.  My experience is that solid state amps tend to flatten the sound stage just a bit and make it more two dimensional.  I am sure there are great SS amps that don't do this, but most of the ones I have heard have this effect, at least to a degree.  A very competent tube amp generally is better at a 3D soundstage, provided the speakers are tube friendly.  Of course YMMV.