One of the nice things about working with Cinemag is their custom design service. This gets us away from the many limitations of standard off-the-shelf transformers from other vendors. We specify source impedance, the range of loads (including capacitance), DC current flow, and expected DC imbalance. They show us what their computer model tells them, we test the physical prototype, see how it works on the bench and in-circuit, and go back and forth a few times until everyone is happy. Off the shelf, it's take it or leave it.
This is what made both the Raven and Blackbird possible. I didn't think a transformer using the 6SN7 in balanced mode could be realized because of the quite high impedances involved. To my surprise, Cinemag showed me otherwise ... very clean square waves at 10 kHz with minimal overshoot. This is not an off-the-shelf part ... it's been designed for us.
When we say the Raven and Blackbird use custom parts we aren't joking. Without them, they aren't practical. We use standard tube types because we want our customers to enjoy them for a long time, and we expect the 6SN7, KT88/6550, and 300B to be around a long time. Under the chassis, though, we use custom parts for critical functions.
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The Raven is not very sensitive to loads. In practice, power amps range from 10K (typical solid-state) to as high as 470K for a handful of vintage tube amps. Most modern tube amps are 100K. Plus whatever cable capacitance is there, along with the Miller capacitance of the input section of the power amp. So 100 to 400 pF is typical. The range of loads is predictable and well known.
What dominates the transformer performance is the source impedance, not the load. The source impedance from the preamp tube is much lower than the load, so it heavily dominates the transformer performance. Transformers don’t much care where the low impedance is, primary or secondary, so long as it is there.
Transformers are aptly named as they transform impedance. They do not isolate impedance. If the source impedance is low that will change the correct loading on the output (as opposed to a high source impedance), which will be found to be exactly one value. Above that value the transformer will ring; below that value it will roll off highs.
This phenomena is well known and is why Jensen Transformers specifies the loading to be used with their SUTs depending on what cartridge is used with them.
If the load is too high impedance, the inter-winding capacitance will come into play as well, causing the FR to no longer be flat, and in extreme cases the transformer may fail to express its turns ratio. The proper termination will yield the widest bandwidth out of the transformer.
This why in the old days when balanced lines were used, the termination standard was always 600 Ohms so the designer would have a pretty good idea of what to shoot for.
A rheostat, placed across the output (between pins 2 and 3) can be used to load the transformer for optimal operation. Or the transformer can be designed for 600 Ohms with a termination switch using a 600 Ohm resistor built into the equipment (this is how Ampex solved this issue on their 351 tape electronics). That way any higher impedance load such as 10K or 100K is negligible and would not affect the transformer performance. The latter approach is why we did with our P-2 balanced line preamp 30 years ago.
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@audioquest4life
I did not make it to the room you mentioned above. I was quite busy running our room with Spatial Audio Lab and only made it to about half the rooms at the show. The link you posted did not work. Can you check and repost it?
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Of course, it is tempting to design a special-purpose headphone amp. I own HifiMan HE1000 Stealth (V3) planar headphones myself, and I use a modest all-in-one DAC/headphone amp to power them.
But ... the headphone amp market is quite crowded, and is dominated by Chinese products selling from $200 to $1600. On the domestic front, Geshelli is cleaning up making AKM-based DACs and Sparkos discrete-opamp headphone amps at entry-level pricing. As far as I can tell, headphones, and headphone amps, is the most competitive sector of the audio market right now.
So even if we spent several months to a year on a special headphone amp, I’m not sure we’d sell many. Something to think about, though.
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In terms of load abuse, plugging planar headphones (20 ohm to 32 ohms) into the Raven preamp will definitely load down the preamp and is not recommended. No harm will result, but the preamp will slide over into Class AB operation and distortion will rise to higher levels. Headphones with impedances of 300 ohms or higher (most dynamics) are fine.
We may design a future project that can accommodate planar headphones, but these require a genuine 1 to 2 watt Class A power amplifier, which is outside the scope of a preamplifier intended to drive power amplifiers. In other words, a tiny but very high quality power amp with extremely quiet power supplies. Designing (good) amplifiers for planar headphones is not as simple as it appears at first glance.
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The Raven is not very sensitive to loads. In practice, power amps range from 10K (typical solid-state) to as high as 470K for a handful of vintage tube amps. Most modern tube amps are 100K. Plus whatever cable capacitance is there, along with the Miller capacitance of the input section of the power amp. So 100 to 400 pF is typical. The range of loads is predictable and well known.
What dominates the transformer performance is the source impedance, not the load. The source impedance from the preamp tube is much lower than the load, so it heavily dominates the transformer performance. Transformers don’t much care where the low impedance is, primary or secondary, so long as it is there.
The hard transformers to design are the interstage transformers, since they are driving nothing more than a grid (without grid resistors). So the load is effectively nothing more than the Miller capacitance, which is fortunately a known quantity and can be designed around. Similarly, the source impedance is also known, since it is the plate impedance of the preceding tube. We use transformers that are purpose designed for the impedances and the power range they will be exposed to in-circuit. (Not off-the-shelf general-purpose transformers.) One nice thing is our transformer designer has access to modern magnetic simulation tools that were not available back in the Thirties and the Fifties.
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Pin 1 is shield and grounded to chassis, pin 2 is XLR + phase and pin 3 is XLR - phase. It will drive any power amp with XLR connections, and will happily drive a 10K amp input impedance.
@donsachs How do you deal with the variable loads which the preamp will be driving? With no feedback, the transformer can ring or express the inter-winding capacitance if its not loaded correctly.
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We just did the sw audio fest in Dallas using the original version and we had one of the top rooms at the show. It really isn't a big change.
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@fthompson251
Hi. It is a very subtle change that I find inaudible, but on paper it is slightly better. The xlr inputs now go directly to the Attenuator and the rca go through a 1:1 transformer to convert to xlr. The previous version ran all inputs through the 1:1 transformer. Honestly, the Cinemag 1:1 transformer is so good that it has something like .25 degree phase shift at 20 Hz. You cannot see it on the oscilloscope and it is sonically transparent. So running the xlr through it was not an issue, but I figured out how to go direct in for the xlr. Again, I changed my preamp and I really cannot tell much difference on the xlr between input transformer coupled and direct. I doubt I could reliably tell in a blind test. The transformer is that good. So if you are using predominantly rca inputs to the preamp there is no change. If you are using the xlr inputs, then there is a change on paper, but you would be hard pressed to hear the difference.
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@lynn_olson @donsachs I’ve been in touch with David Whitt about the pre amp, he said they are shipping the first build cycle in May of this year. He also stated that there is a 6 week build cycle. It seems you are still making changes to it at the moment, at least from what I gathered in this thread? Would it be wise to hold off a bit for a couple months until you determine the final product? I am not in a hurry, but searching for my end game preamp and want te best version of it.
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@fthompson251
I understand, retubing 8 300bs can certainly add up. I hope your VAC REN 70/70 finds a wonderful new home. I can also understand the desire to simplify one’s audio system.
Charles
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@charles1dad Yes, it was a very tough decision but I cannot lift the damn thing anymore and re tubing it is nearly $2000. I want to simplify my retired life a bit. I just picked it up from VAC and it is fresh as a daisy for the new owner. New tubes with about 100 hours on them.
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@fthompson251
Is the Coda amplifier replacing your iconic VAC Renaissance 70/70. amplifier? I have no doubt that the Raven preamplifier would work marvelously with either.
Charles
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OK thanks @donsachs and @lynn_olson I missed that price when I looked at it the first time online. A significant point you made Don is the fact that it will "happily drive a 10K amp impedance" I have a new Coda amp on order and the XLR input is exactly that! I sent some questions to Spacial Audio regarding deposits and time it will take to get one. I want to keep a tube preamp in the drive train. My old one was 25 years old! Thanks!
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I fully defer to Don, who is part of the loop of the Spatial team, who manufacture the preamp and power amp. I’m more like the system architect, guiding the project in a certain direction, and I’m not as aware of the manufacturing and production side of things.
One benefit of the output transformer in the preamp is it does accurate phase spitting, even if there is a small gain mismatch in the 6SN7 tube. Other balanced designs tend to rely on feedback for output balancing ... the Raven is zero feedback, either global or local, so transformers do the balancing and unbalancing conversions.
The input transformers are bypassed for the special case of XLR (balanced) sources. For example, many DACs have XLR outputs, since many converters inside the DAC have balanced outputs. On the other hand, tube phono preamps are often single-ended, so have RCA outputs. The Raven caters to both, with a source selector on the remote control. The Khozmo volume control is fully balanced, and so is the 6SN7 that follows it.
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I believe the preamp is $5500. Search for spatial audio lab, find the site and look at the revelation series and preamp and you will find it. On the preamp, it is fully balanced and transformer coupled to output. Pin 1 is shield and grounded to chassis, pin 2 is XLR + phase and pin 3 is XLR - phase. It will drive any power amp with XLR connections, and will happily drive a 10K amp input impedance.
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To the best of my knowledge, the price of the preamp is $5000. Possibly less when purchased as a bundle with the power amps. The XLR output should be AES compliant, driving both phase equally.
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I'm very much hoping their is a build thread for the Speakers to be designed.
This is an area I am progressing into, as I have recently on a few occasions heard Speakers that are a a bespoke design and are as a end sound, what I believe are a challenge to my ESL's.
My personal preference for a Speaker does seem to have changed and a curiosity is now taking hold.
Even the idea of modding owned Cabinet Speakers and attaching Internal Wiring to a Drivers Voice Coil as suggested by another Speaker Builder on here, has my curiosity and is intended to be experienced when advisories are offered.
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@lynn_olson - Is the Raven Preamp AES48 standard balanced? They don't have a price listed for it that I can find.
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A local store builds and sells their own high end tube gear and their own horn-based speakers. For most of their demonstrations of the better horn systems they use their 350B amplifier. One day when the boss was away, two of the younger employees spent the afternoon swapping in speakers acquired in trade-ins to see how they sound. While all the speaker sounded quite different, they all sounded amazingly good to these two. They could not believe how good even Polk speakers sounded. It then dawned on them that the amplifier mattered a lot. One did not get that kind of "transformation" of the speaker with the likes of Conrad Johnson amps, for example. That is not to say that the CJ isn't good, it is just that the 350B amp had a particular character to its sound and that character played well with a wide range of speakers.
I tend to find that tubes related to the 350B do sound nice with a wide range of gear. I tend to like 6L6 and KT 66 tubes (similar to 350B). I run a somewhat similar, albeit much less powerful tube, the 349 (in pushpull) and I like it a lot.
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I got into the amp game after auditioning both the Audio Note Ongaku and the Reichert Silver 300B on speakers of my own design. I’ve been designing speakers since 1975, so I have a pretty good idea what goes in them and why they sound the way they do. Crossover design errors, diffraction artifacts, enclosure resonances, driver breakup, etc. are things I usually hear in a few seconds when I listen to commercial speakers. So I know speakers pretty well.
What surprised me was the Ongaku and Reichert revealed things about my speakers I did not know were there. And different things between the two: the Ongaku revealed "space between the notes" in a way I had never heard before, as well as extraordinary, almost uncanny spatial realism. The Reichert deepened the emotional response to the music in a way that was outside the audiophile experience and not anything to with coloration or tonal balance. It was just a feeling, even when I was listening objectively and trying to assess what I was hearing. It just snuck up on me with a powerful emotional response.
It’s one thing listening to a commercial speaker that’s off-the-shelf with unknown design goals, semi-custom drivers, and unknown crossover design, but quite another when the speaker is something you’ve taken from initial conception to successive versions to final prototype. You’ve pretty much heard everything it can do, and have already built 13 different crossover variations and auditioned it on eight different amplifiers. You know that speaker inside and out.
And yet my speakers had undiscovered sonic aspects that were NOT part of source impedance (damping factor) or audible amplifier coloration. Things I’d never heard before. What kind of "distortion" gives MORE resolution, or a deeper, more profound emotional response? That’s nuts. Nonlinearity is not our friend; it steals resolution and separates you from the music with a haze of coloration.
So what’s going on here? That’s when I started researching the history of vacuum tubes and started writing for different audio magazines. I don’t believe in copying or "cloning" the designs of others; not only is it dishonest, it reflects a lack of understanding on why a product sounds the way it does. You have to understand the "why" before you can go any further, and that took about five years before I came up with the Amity in 1997.
Amplifiers are not as neutral as we would like them to be, and an amplifier with measured distortion in the parts-per-million range is not necessarily neutral sounding. They all have a sound ... Class D, GanFET, bipolar transistor, pentode, triode, and direct-heated triode.
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I agree that the amp plays a very big role in the sound, and perhaps, too little attention is paid to the amp. Far too many pick their speakers first, and then think finding the suitable amount of power will be the primary task in picking an amp.
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Yes, I've come to the conclusion that speakers and power amps are about 50/50 responsible for overall sonics. Based on measurements, you'd think that speakers are responsible for 90% of system coloration, but in practice, no. The amps have a big role, too.
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Alexberger,
You are sure right about that. I have Don Sachs new preamp and his shoebox 300b monos and swapped out my Cube Audio Jazzon speakers for a pair of updated AR 2ax speakers and they sound extremely musical. A great front end yields benefits no matter what speakers you have. Rest assured, the Cubes will be back in my system shortly.
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Many audiophiles underrate the contribution of pre and power amplifier in sound systems.
In most cases an extraordinary amplifier with average speakers sounds better than an average amplifier with extraordinary speakers.
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If Spatial is at the Seattle show this year, yes, I will be there. I had a lot of personal stuff that precluded my attendance at Dallas, but it sounds like the SWAF was great experience and a good time for all.
Don tells me there is a lot of serious tech in the new Q3 speaker, and of course Don and I have rolled in a lot of new tech into the preamp and power amp since the Seattle show.
I expect I’ll be working with Joseph Troy Crowe on completing the notorious "Beyond the Ariel" speaker project started many years ago on DIYaudio. This will be a non-Spatial project, just between me and Troy, but it will be open-source.
My work with Don and Spatial will continue ... in the short term, I need to write the product manuals. If there is demand for new electronic products, I will be part of that, but Spatial designs their speakers with their own design team in Salt Lake City.
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I just returned from Dallas, and I have to tell you that our room was one of the top two or three in the show. Danny Ritchie (GR Research) came by and told us our room was his pick for best sound of the show. Sam Whitt, the speaker designer at Spatial, just completely nailed that new Q3 speaker. It is superb.... Of course the preamp and amps driving it didn't hurt either:)
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Spatial Audio at the Southwest Audio Festival, with the new Q3 dual 15" dipole speakers and the latest Revelation Series Raven preamp and Blackbird power amps. The pint-sized Mola Mola Tambaqui DAC is tucked behind the Raven preamp.
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Any inquiries to purchase from the UK as of Yet?
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Still making small production changes to the Revelation Series power amps and preamps. The main B+ power supply choke (filter) is now from Monolith Transformers and is on top of the chassis, along with the output transformer and the power transformer.
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Spatial Audio now has the preamp and power amp in production (scroll down about halfway). The power amps are now 18" wide, the same as the matching preamp.
The tube lineup is 6SN7 input (balanced), triode-connected KT88 drivers, and 300B output in a fully balanced zero-feedback circuit. Monolith custom-design power and output transformers. The VR shunt regulators are on the right side of chassis, along with the power supply circuits. The audio circuits are on the left side, isolated from the power supply by an under-chassis shield running from front to back.
Revelation Series
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I finished my integrated 300B SET project with two external power supplies.
It took me about 40 hours to drill chassis (thank you for my friend who helped me do it) and to assembly all parts together.
The amplifier sounds from scratch batter than my previous DIY amplifiers which was disassembled for parts for the new project. And it should sound much better after break-in.
Thank you guys for helpful advices.
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I did most of those things for the Seattle trip. I hadn’t flown in more than a decade, and I knew it would be Hell on Earth if I didn’t tick all the boxes. So, in the months preceding, I applied for TSA Pre-Check, Instant Bag Check using the QR code on the phone, Early Boarding (for a fee), Lounge Access (lounge was closed), and Extra Seating Room (because I’m 6’ 1").
Most of it worked perfectly. TSA Pre-Check was fast and efficient. Instant Bag Check, likewise. Early Boarding, same. Extra Seating Room, yup, and pre-checked into a window seat both ways. Check. All perfect and worth every penny.
But ... the *&$@# concourse in Denver Airport was miles long, and there are several of them, connected only by a standing-room-only subway. And United changed the gate THREE times, sending a text to my phone just after I hiked all the way to the end of a concourse A, only to find no flight to Seattle after getting there. So then the flight is changed to the end of Concourse B (walking all the way back, taking the jammed subway, and walking all the way to the end of ANOTHER concourse), and then it got changed a THIRD time, right back to the end of Concourse A.
It must have been at least two miles, and there is nowhere to sit on this trek. Hey, airports are supposed to be ADA compliant, and I’m a tired old geezer about to fall over. So I ask a porter, can I get a ride in one of those ride-alongs I see whizzing by. Nope, you have to reserve a seat at least a day ahead with the airline you are flying on. No ride for you!
So ... the airport is grossly out of compliance with ADA unless you reserve at least a day ahead. Too bad if you are a single mom with an exhausted toddler, disabled with a crutch, or just plain old, like me, You get to walk, and walk, and walk, and if you fall over, well, tough. That’s your problem.
Oh yes, and I got Covid when I came home, almost certainly in the Denver or Seattle airports, which are both jammed each way. And then Karna got it 36 hours later, from me. Fortunately, Paxlovid dispatched it in a couple of days.
So I learned two things: wear an N95 mask in the airport, jetway, and airplane, until the airplane A/C is turned on. There’s plenty of fresh air on the flight (especially if you’re flying on a nice breezy Boeing 737 Max).
Second, reserve a wheelchair (by Federal law, no extra charge) at each end of the journey. The walking distances in both Denver and Seattle airports are stupendous. I felt truly sorry for the disabled folks and single moms ... they were at the ragged edge of endurance, with nowhere to sit and pause for a moment. The absence of any seating in the concourse is a scandal, and frankly, a health hazard for some of us.
Aside from the concourse horror, things went fine otherwise. Flying is fine if you have early boarding and a roomy window seat. TSA Pre-Check is worth the $80 charge and the FBI background check. I lead a boring life, there’s not anything to find.
And the show itself was great, as I expected. Sure, it was possible I was exposed to Covid at the show, but I doubt it. The airports were the human zoo, with tens of thousands of stressed-out people shoving past each other.
I very much miss the Portland to Denver Amtrak train, which was wonderful. Book a sleeper compartment and watch the countryside roll by. That was a wonderful trip.
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@lynn_olson After Seattle last year, I made sure that I got pre-checked from TSA. Something like that can make your life much more pleasant.
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Don and the Spatial team will be in Dallas, but I will be home here in Colorado. If Spatial goes to the Seattle show this year, I will be there along with Don.
I learned my lesson about flying last year. This time, I’ll fly First or Business Class, and will wear an N95 mask while I’m at the airport. The show, though, was a lot of fun, and it was really nice staying at the show hotel and taking a nap in my room when I needed a brief rest. Also great meeting you folks in person, and seeing (and hearing) what’s going on in the industry.
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No, not that I know of. Dallas, and then I think they are planning on going to Seattle again in early Sept. You should write them to see if they are planning on going to the east somewhere. You can contact them via their site.
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Hi @donsachs ,
Will Spatial be in the Montreal AudioFest on March 22-24 ?
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Just a note that Spatial will be at the SW Audio Fest in Dallas, March 15-17. They will have the final production versions of the Raven preamp and Blackbird mono 300b amps driving their speakers. I will be there all day Friday and Saturday, and a bit on Sunday morning. So if you are in the general vicinity and want to hear this gear please stop by! We will have tons of music on a hard drive, and if internet Gods are willing we will have Tidal and Qobuz available to queue up requests.
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Maybe Peregrine. Something fast and powerful, which are the hallmarks of these designs.
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Well, they are really fast:)
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Alright, so the Grackle? Rook?
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@downtheline Actually, next up is a two stage amp with another lovely DHT in push pull for a whopping 3-4 watts at very low distortion. Not a 300b so not for this thread! You could hang a custom transformer off it for phones. You would want a REALLY good custom little transformer for headphones. Not some off the shelf average quality solution. Anything worth doing is worth doing to excess. It would work and drive darn near any cans you would want to plug in. You could even have multiple windings and perhaps a switch or two output jacks. One for 300-600 ohm cans and one for the planar crowd. Maybe in a few months.. First we get the Blackbirds and Raven off the ground (pun intended). We have just built the first ones in Utah and I expect sales in Feb. Then I can focus on other projects....
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Sounds like the next project for your collaboration is a headphone amp for a wide impedance range of headphones!
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As an overview, the Raven is a 1-stage amplifier with a 4.5:1 step-down transformer, and is output-limited by what both sections of a 6SN7 can crank out. The Blackbird is a 3-stage amplifier with a 28.7:1 step-down transformer, and is output-limited by what a pair of 300B’s can crank out.
The ideal solution for planar headphones is a 2-stage amplifier. For example, in the xDuoo TA-10R headphone amp sitting right next to me, a 12AU7 followed by a pair of Class A emitter-followers for each channel. Simple and inexpensive. Or, small power amplifiers in the 2 to 5 watt range ... all transistor, hybrid, or all-tube. The all-tube solutions ideally use step-down (output) transformers to match the load to the capabilities of the output tube.
Vacuum tubes can swing lots (hundreds) of volts, but are current-limited by peak cathode emission, typically measured in tens of milliamps, not amps. Bipolar and MOSFET transistors, in contrast, can pass not just milliamperes, but several amps, which is why they can be direct-connected to low-impedance devices like 8-ohm speakers and 20-ohm headphones.
A quick note on transformers: the voltage/current transformation ratio is the same as the turns ratio, but the impedance ratio is the square of the turns ratio. For example, the output transformer of the Blackbird, and many other other push-pull amplifiers, has a primary impedance of 6600 ohms, and a secondary impedance of 8 ohms. 6600/8 = 825, and the square root of 825 is 28.7228, which is close to the physical turns ratio. In a well-designed transformer, total losses are less than 5%, so can be neglected for this calculation.
So the output transformer of the Blackbird multiplies the peak current of the 300B pair by 28.7 times, offering peak currents of several amps to the loudspeaker. Similarly, the output transformer of the Raven multiplies the peak current of the 6SN7 by 4.5 times, which is plenty for driving a cable, but not really enough for planar headphones which mimic loudspeakers in terms of current draw.
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Got it thanks! Will need to replace my lcd-x!
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@downtheline The Raven has a headphone jack, yes, but as Lynn noted, it will only drive the typical old style phones. It will not drive planars. Sounds great with my old Sennheisers and phones of that type with 300 ohm impedance.
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