if you can fit a toroid in there, then look at the antek site. They have small filament transformers and may have what you want. AN0205 is 25VA with dual 5V windings so will give you 2.5 A x 2. They are fine for what you want. they also sell transformer covers. If you want to regulate the filament supply for each 300b then you can get a 2 x 7V.
300b lovers
I have been an owner of Don Sachs gear since he began, and he modified all my HK Citation gear before he came out with his own creations. I bought a Willsenton 300b integrated amp and was smitten with the sound of it, inexpensive as it is. Don told me that he was designing a 300b amp with the legendary Lynn Olson and lo and behold, I got one of his early pair of pre-production mono-blocks recently, driving Spatial Audio M5 Triode Masters.
Now with a week on the amp, I am eager to say that these 300b amps are simply sensational, creating a sound that brings the musicians right into my listening room with a palpable presence. They create the most open vidid presentation to the music -- they are neither warm nor cool, just uncannily true to the source of the music. They replace his excellent Kootai KT88 which I was dubious about being bettered by anything, but these amps are just outstanding. Don is nearing production of a successor to his highly regard DS2 preamp, which also will have a unique circuitry to mate with his 300b monos via XLR connections. Don explained the sonic benefits of this design and it went over my head, but clearly these designs are well though out.. my ears confirm it.
I have been an audiophile for nearly 50 years having had a boatload of electronics during that time, but I personally have never heard such a realistic presentation to my music as I am hearing with these 300b monos in my system. 300b tubes lend themselves to realistic music reproduction as my Willsenton 300b integrated amps informed me, but Don's 300b amps are in a entirely different realm. Of course, 300b amps favor efficient speakers so carefully component matching is paramount.
Don is working out a business arrangement to have his electronics built by an American audio firm so they will soon be more widely available to the public. Don will be attending the Seattle Audio Show in June in the Spatial Audio room where the speakers will be driven by his 300b monos and his preamp, with digital conversion with the outstanding Lampizator Pacific tube DAC. I will be there to hear what I expect to be an outstanding sonic presentation.
To allay any questions about the cost of Don's 300b mono, I do not have an answer.
Showing 50 responses by donsachs
I have explored all sorts of variants of this basic circuit for about two years now, and have learned what I like and understood why. This is a deceptively simple circuit, except that there is subtle complexity. Often, we get caught up in the conventional way of doing things, and then spend all our time refining them to try and hide all of the problems and colorations. Sometimes we need to think outside the box. I left traditional power supply design for tube amps probably 5 or 6 years ago. There are huge threads on the sonics of various capacitors in speaker crossovers and amplifiers. Trust me, I have heard many of the top caps. The best cap is no cap. It took time to arrive at that notion. Time that was wasted auditioning top capacitors instead of thinking outside that box. As we discussed earlier in the thread, your alternatives are to either directly couple tubes, or use transformer coupling. Both have advantages in different sorts of circuits. In this circuit, transformer coupling is best because of the balance at all stages, which is the key to this amp. Think of it as constantly canceling distortion and balancing itself. But you cannot just buy off the shelf transformers from company L or H or E or whomever. For this circuit you need interstage transformers that are optimized for the loads they see and can give flat response from below 20 Hz to above 20 KHz with little or no phase shift. That is no easy task, and you have to work with a very experienced winder and it takes some prototyping and testing. Well, over a year of prototyping and testing. It is not an accident that the best of the vintage tube amps had killer transformers. So, as Lynn elegantly stated above, this circuit is totally revealing and even though you have relatively few parts in the signal path, they have to be really good parts, and some of them have to be custom designed to get the best performance. The audio circuit looks trivial, except that it isn't trivial to get that hand full of parts to work really well together. Two years ago I would never have built a cathode biased amp, and I resisted that notion at first. Then I thought outside that box and understood what this circuit was doing and why the cathode biasing was best. I had the notion that all cathode biased amps sound slow and syrupy and deliver far less power than a fixed bias alternative. Well, in a conventional circuit that is correct, but not in this one. The power supply is also highly optimized and we use some tricks to further isolate it from the audio circuit, and ways to isolate the input tube from the driver circuit power supply. Of course the 300b supply is separate from the driver and input supply. The filament supplies also are regulated and isolated from each other. So there is a fairly complex, yet very conservatively rated and reliable power supply that drives this subtly complex, but fairly simple circuit. If you change one thing you instantly hear it. So, in this amp there was quite a bit of tuning, again, to remove coloration. The result is a transparency I have not heard in any other amp to date, plus the ability to drive quite an array of speakers. Again, don't let the 27 watts fool you. Is this a perfect amplifier? Of course not. There is no perfect amplifier. Again, if I were to magically create a straight wire with gain and play it for 100 folks, half of them would love it, and half would probably hate it. This amp's hallmark is utter transparency and tonal correctness. The piano is in the room with you and you can easily tell a Steinway from a Bosendorfer. I realize that most everything I have heard to date is quite colored, or if fairly neutral, lacks the resolution of this circuit built this way with these parts. This circuit is uncolored, transparent, and highly resolving, and has a boatload of driving ability. It packs serious punch. Unlike a single ended amp, where the idea is to tune the coloration inherent in the design to suit your taste, this project was about removing the coloration so the circuit could really shine. Trust me, it doesn't sound cold and clinical. It sounds like music with all over the overtones in the instruments, the inflections of the voices, etc... It is not sterile sounding at all, but rather it invites you into the music. To each their own, but this amp is wonderful to my ear and ready for production and this thread has been an insight into our design choices, and the journey. Others make other choices and that is as it should be. I have no desire to build a 200+ watt amp to drive a very difficult speaker, but I do want to drive most speakers in most rooms. |
... Actually, sonically the statements and the Blackbirds have similar heritage, but the Blackbirds are much better. The Monolith Magnetics iron is just sublime, plus the power supply is improved in several ways including the addition of the pair of VR tubes. The result is the Blackbird kicks it up a notch from the Statements, which were sort of a final prototype before we just pulled out all the stops and made the cases larger on the Blackbird. I just returned from Utah, where I taught the guys at Spatial the builds of both the amps and preamp. There will be actual units for purchase in January. |
@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. |
@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.... |
Hi all... Mark wrote and said he posted something so I thought I would chime in. The amps are push pull 300b monos and are 27 watts/ch. Not your flea watt 300b. It has been a really fun project with Lynn Olson. If you aren’t familiar with Lynn, just google nutshell hifi. Not your traditional push pull with phase split circuits though. A different approach. No feedback. Just a single pair of 300b tubes in each amp. Drivers are 6V6 with 6SN7 input tube. Multiple power supplies in each amp. We have driven 86 dB 4 ohm speakers quite easily with them to screamingly loud levels. They are 27 watts, but seem to have the drive of a 100 watt tube amp. The prototype amps along with their matching preamp will be demonstrated at the Spatial Audio Labs room at the Pacific Audio Fest in Seattle in late June. I have even talked Lynn Olson into coming. Should be fun! No production of anything yet. Hope to get that going in the late summer or fall. Not trying to sell anyone anything here, just letting you all know what is in the works.... Mainly we are just having a lot of fun pushing the envelope a bit. I am slowly trying to retire from production of things to more projects like this one. Trying to see what is possible with a little "outside the box" thinking. Happy Listening and hope you are all enjoying your stereos! Don |
HI It is really not my intent to get into detail here for something that is in prototyping. Yes, there have been many balanced tube preamp and amplifier circuits around for years, and I have absolutely no doubt you build an excellent balanced preamp as I know you guys build really good amps as well! This is a slightly different approach to a traditional tube circuit, and yes the transformer coupling is part of it. Also, as you well know, the quality of whatever attenuator you use is critical, and of course the power supply. Anyway, I think I am going to bow out of this thread because it was never my intent to do business here. That is inappropriate and there is nothing to sell yet anyway! Just was commenting to tell folks what I was up to in my semi-retirement. See anyone who wants to chat in Seattle! |
HI My Pacific is XLR out with no volume control so have not tried direct to amps, but I build a really good preamp so I will continue to use it. The prototype preamp is essentially a circuit that was a thought experiment of Lynn’s for a fully balanced design that has been around for years and no one ever really tried to build and perfect it. So we did for this project. Like the amps it is conceptually simple, yet has subtle complexity. It is transformer coupled on both inputs and outputs and uses the same Khozmo 64 step remote attenuator with relay input switching I have been using, but set up as dual mono. This allows me to switch a balanced signal on both channels, plus you get a balance control if you need one. Main tube is 6SN7 and it is transformer coupled to the output with custom wound iron from Dave at Cinemag for just this circuit. I have tried ECC99 and 6H6P with adapters and they also sound good, but I always pick the 6SN7 in a shoot out, so it has octal sockets. The power supply features damper diodes into a CLC and that drives a custom regulated supply which then feeds gas regulator tubes. Because of the output transformer it can easily drive RCA or XLR outputs and headphones. It has no caps in signal path and of course no feedback or anything like that. If you use the preamp xlr outs you can drive the amp input tube grids directly. It has a level of clarity that has to be heard. Quite astounding. The prototype works well and I am working on the "real" one for the Seattle show. Dave’s iron is just superb as it always is and response is dead flat from below 20 Hz to way out there beyond 20KHz. Just having fun and we will see where it all goes. Honestly I have never heard anything like this setup.... fun. |
The post from @pindac above is spot on. Most people think a 300b is a fuzzy rolled off tube. That is because they heard it in a single ended amp with a mediocre power supply, and most likely an inadequate driver section, and possibly mediocre output transformers. Such as all the entry level Chinese 300b amps. They still are pleasant to listen to, but if you use a really good driver section that never clips before the 300b tubes do and is capable of driving the capacitive load of the 300b, a really killer power supply, actually multiple ones, and really good transformers, the 300b will walk all over any of the normal output tubes such as kt88, el34, etc.... That is what @whitestix heard.... A PP 300b amp done right is very special. I really had no idea how good they were until I spent a year working on one. See some of you in Seattle. |
Absolutely. I read a great quote somewhere about a million years ago, that a great tube amp was the sum of three things. How good is the circuit? How good is the power supply? How good are the transformers? If you take care of all three of those things you get a great amp with most any tubes. Most commercial designs that are built to low price points make serious compromises in one or more of those areas. If you take care of business, you generally get a great amp. |
@antigrunge2 Glad you have an amp you love. What I meant above is the design of the driver section of the circuit. Your amp is using a 6L6 to drive a 300b, which is a good choice. I was referring to many 300b amps that are pushing tubes like a 6SN7 to the max and barely driving a 300b. The first rule of amp design is your driver section should never strain or clip before your output section does. As for the SET vs PP on musicality and soundstaging, well I would submit you've never heard a push pull 300b amp designed like the one Lynn and I have been working on. You might be surprised... |
Hi The 6SN7 will barely drive a 300b, which is a very difficult load. I have not worked with 845 tubes nor will I given the high voltages and heat involved, but I did look at the data sheet. Yes, it takes more negative grid voltage to bias one than a 300b, but I have no idea of how capacitive a load an 845 is, and I really don't have time to research it. Ralph is right in that a 6SN7 is adequate to drive many tubes. It makes a wonderful driver for any of the usual octal pentodes like kt88 or el34, or a 6V6 or 6L6. Works great. But a 300b taxes a 6SN7. It works as in the original Reichert amp, but if you want to unlock the unlimited dynamics of the 300b you need a much better driver setup. The reason the original Dynaco ST70 was a marignal amp was it had a wimpy driver section that would clip before the output tubes, or about the same time, plus it had a very mediocre power supply. It was a pleasant amp and a zillion of them sold. But if the driver and power supply were better it would have been a much better amp. The output transformers are not world class, but they are quite good and capable of more than the rest of the amp could provide. You can also improve the performance of any driver tube by changing the way it is loaded. For example, a CCS will give far better drive capability than just typical RC coupling. But CCS circuits do have some coloration. Not so bad in a pentode amp, but very noticeable in a DHT amp. The other ways are to add inductance to the plate of the driver with either LC (choke cap) coupling or full on interstage transformer coupling. The inductance the driver tube plate sees "helps" it out to drive the 300b. There are differences in the way all of these approaches sound, but all are better than just a plate load resistor and coupling cap. I have explored all of them thoroughly for a year with the 300b project and found a solution that Lynn and I like and sounds the most musical. |
I used the 6SN7 to drive both KT66/6L6 and KT88 in two different amps and they are great for that. They are marginal to drive a 300b. As @atmasphere said, there are many approaches and schools of thought about drivers. Many paths to audio nirvana as it were. There are also many power supply approaches. As for SE vs PP, well, traditional PP has issues with phase splitter circuits right in the middle of them, and SE amps do have certain types of distortion. These amps do PP a different way and limit the phase split issue and avoid some SE distortion. Again, there are many fine examples of all sorts of amp topologies, but these don't sound at all like other PP amps you have heard. They sound like a great SE amp with the drive of a PP amp. That is the design goal.... |
No, I am not going to do kits... I am retiring and letting a partner build the 300b project and matching preamp. That should be going before the end of the year. If you make kits you have no control over how they are built and you get LOTs of questions so customer service is a big issue. Just because most folks are competent and can build a kit, even if only 5-10% of people are in over their heads you get a support problem. It is far easier to build a product, test it, and then warrant it. Plus, these amps use multiple regulated supplies per amp, and it took a while to work it out and get it right. They are very stable when built correctly, but not trivial to do the build. They are designed to be easy to service as well, but kits... no. The amps need about 1.5 volts for full output so any preamp can do that. They also feature XLR inputs, which are very easy to drive. I a quite smitten with this design and think they sound great, and of course I have not heard all the other great amps discussed in this thread. Hopefully someone who comes to Seattle has and can tell me their opinion! |
@carlsbad2 Yes the Reichert amp used 6SN7 to drive 300b and though I have not heard one, those who have said it had a sonic purity that was hard to beat. So it was a good starting point and 6SN7 driving a 300b can sound good. But it can be improved if you are looking for all out performance. |
As Lynn was saying above, I have spent the last year working on this 300b amp project and the matching "Raven" balanced preamp. Spatial Audio will decide on final naming and pricing and I will help them get started on production. The cosmetics will probably change a bit, but the circuits are stable and that is what will be shown in Seattle. This thread has mentioned many fine amps and as I said, there are many paths to audio nirvana. Lynn and I have had fun with this project and we want to see it out in the world. It is cost no object, sort of within reason. The gear isn't going to cost $50,000, but it also isn't going to cost what the current Kootenay amp and preamp cost either. These are much more expensive to build and more involved. If you can hear them in Seattle please drop by. Honestly, I would love to hear people's opinion!
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@tinear123 The pricing and availability isn't set yet. Most likely Cloud Sessions of Spatial Audio Labs will keep a wait list and they will have to decide on whether there is a deposit required, final pricing, etc... Once we have it all ironed out there will be an announcement on the Spatial Audio Labs site. First the official unveiling of the prototypes at the Seattle show on June 23. |
As they say, if you literally built a straight wire with gain half the people wouldn't like it:) Everything has a sound. I will say that these amps have far less of a sound than anything I have ever heard... or not heard... or whatever... They just seem to remove themselves and just leave this cloud of music in your room. Pinpoint imaging, but it is like omnimax for the ears. That is my take. I will be interested to hear what other people think in Seattle. |
As Lynn mentioned above, we chose the 6SN7 and the 6V6 because both are in current production and there are very good modern versions of each being built. Obviously there are lots of 300b choices as well. I favour the Linlai E-6SN7 beause it sounds wonderful and is reasonably priced. The JJ 6V6 sounds quite good. I love the old stock Russian black bottle 6V6 in here and you can still get them for reasonable prices out of Ukraine, Romania, and other places without sending money to Russian vendors at this time. You do need pairs that are within maybe 2 mV of each other for full bass performance in the amp. Matched pairs of 300b for the same reason. They are all readily available, and the amp runs tubes at sane operating points so they will last a long time. We didn't want to produce an amp that required really expensive tubes that could be unobatinium in a few years. |
..and what Lynn is not saying is that these amps address these problems. Without going into proprietary detail, I will say that there are two separate power supplies in each amp and that every tube plate in the amp has a healthy inductance between it and the power supply that feeds it. These things add up:) The matching preamp also is transformer coupled and has a ridiculously overbuilt power supply. The 300b is incredibly extended at both frequency extremes when you can drive the heck out of it....... It is not slow and syrupy at all, but rather it has lighting transient response and stunning bass. If driven correctly..... |
I make a change and live with it for at least a few days or a week before deciding. Yes, the film caps have to run in. With this amp project I built a stereo version first because I had a few of the Kootenay amp cherry cases laying about. So I made it all fit. There are different topologies to try. The first was full "silicon assist" where the driver tubes each have a CCS on the plates. I took this version to Spatial Audio a year ago and we all agreed it was the best amp any of us had heard. But then I tried LC coupling and it was better to my ear. So then I had Dave Geren of Cinemag design me a custom interstage transformer for just this circuit. As Lynn said above, the 300b is a hard tube to drive. Dave likes a challenge, and his interstage transformer sounds better than either previous version. The IT version is more "musical" and "relaxed" sounding, yet has an insane level of detail. Then we decided to go to mono blocks because we could improve the power supply considerably with more space to play with. So my point is these things evolve over a year or more and I listen to each variation for quite a long time. The mono 300b amps going to Seattle for the show are the result of a year of listening to different ways to build the circuit. You have a pair of them and they are pretty special to my ear. It took a lot of experimentation, guided by theory to get to this point. That and patience of course.... |
When I "voice" amps and preamps I am always trying to make them sound like they are not there. I have a Lampizator Pacific DAC so the front end is killer. I am always trying to have the amps vanish. That is the goal. They should just sound like music and not be warm or cool or anything. Lynn's circuit is amazing. If you put a really good power supply in front of it and really good output transformers behind it you get the vanishing act...... I "voice" things mostly with recordings of acoustic instruments and vocals of course. Does the piano or mandolin sound real? So I have my favorite 100 test tracks. Of course I enjoy Pink Floyd or a live Dead show, but you don't really know what the electric guitar is supposed to sound like. That sort of music will tell you if your amp rocks, but not if instruments sound convincing. I know what a mandolin or stand up bass sounds like. I love David Grisman's acoustic disc label. I love the last recording of the Goldberg variations that Glenn Gould made. If I can easily follow the left and right hands with no strain, then the amps are good. I really like Myriam Alter's compositions. She plays on some of them, but they are always interesting music with hints of Klezmer and all sorts of other influences. They are usually 3 to 5 instruments, like piano, clarinet, bandoneon, and interesting percussion. If you can easily follow an individual instrument or switch to listening to the whole, then the amp is good. I find this circuit to be FAR better than any amp I have ever heard. The reason is that it avoids many sorts of distortion that plague other circuits. You don't really know you are listening to all of that until it is gone, or at least very minimized. So what you hear is really the lack of all the other things you usually hear in other amps. That allows only the music to remain, floating in the air in your room. I find it quite astonishing after all the years of restoring classic tube amps, and then building my own, to hear what this approach brings. Very enlightening. |
Actually Lynn said if I built the Symmetric Reichert it would be the best amp I had ever heard. I like a challenge. Then I decided if I was going to build it we would figure out the best way. So we ditched the driver section and came up with a much better one, and I prefer power supplies done my way, to the max so we worked on that approach too. A year later here we are..... |
As I am retiring from constant production of tube gear I wanted to see what was possible. How good could it sound? Lynn got me to look at the symmertic Reichert circuit and it looked interesting and off I went. Then he showed me the Raven preamp circuit, which like that amp is deceptively simple at first glance, but there is a subtle complexity to both. The Raven took some doing to get it to take XLR inputs as well as RCA and to do so with the remote contolled Khozmo attenuator that I favor in my previous preamp. There were things to figure out. We did the same dance with power supplies, building it several ways and then decided to combine both the modern regulated approach with the VR tubes. The combination is quite astounding. So all of this is about having fun and seeing what is possible. I could build a DHT preamp with the 26 tube, but there are few to buy. I kind of wanted to see how good a 6SN7 can sound, and the answer is exquisitely good if done right..... without all the hum potential and microphonics, and cost of the DHT apapproach. So it is about balancing things, using tubes that are readily available and seeing what is possible. Now someone else can build them in commercial quantity! |
I will also add that for the preamp, I built one with off the shelf Lundahl transformers and then again, I got Dave Geren at Cinemag to wind me the best small output transformer he could after I showed him the circuit. Better....... Very transparent and no coupling caps anywhere! But plenty of current drive to make cable choices far less important, which is one of the features of the Raven circuit. Plus the transformer coupling allows for XLR or RCA output and it will happily drive headphones. Will easily drive even a 10K amp. So if done right, there are lots of advantages to a transformer coupled preamp. I can say that I don't miss coupling caps at all, note even the really good ones I was using previously. So again, for me it is about seeing what was possible and then refining it. |
As I said, there are subtle complexities in what appears to be a really simple circuit when you first look at the schematic. I am sure the symmetric Reichert sounds great, but I am sure it cannot touch the current build due to all the improvements we have made in the past year. It has been quite a fascinating project for me because I thoroughly understand all the vintage circuits having rebuilt more vintage tube gear than I can count, and then building my own with improvements to the power supply and signal path, but basically the same approach as all the classic tube gear. This approach is completely different and I have learned a lot in the past year. The result is an amplifier, and a preamp that don't sound like anything I have ever heard before. Well, really, they sound less like anything at all and more like music. @whitestix has the first pair of mono 300b amps that I let leak out into the world and he started this thread. We have never met, but talk on the phone now and then and he has had a version of pretty much everything I have ever built over the years. So I thought it fitting that he should hear these. I didn't tell him to start a thread and certainly had no idea it would go on this long! |
@atmasphere So many paths to audio nirvana. So many tubes, so little time:) |
To distill much of the above. What struck me (well, Clayton and folks at Spatial Audio as well) with the first build of the circuit in a stereo box with a CCS on the plate of each driver tube was the purity of the sound. It didn't have a sound per se. The amp just got out of the way. The first prototype of the Spatial X4 fully passive speaker with the new crossover was there. It was about 87 dB and 4 ohms. The amp drove it with ease. One of their techs, who is a lot younger than I, liked it LOUD. I went out to grab lunch and when I came back, Ryan had it cranked so loud I could not be in the room. No strain, no clipping, no nothing. It just got louder. He said it played as loud as his Schiit mono block SS amps, and sounded FAR better. It indeed sounds like a 60-100 watt tube amp for drive, but it sounds far better than any other amp I have heard. Of course we have spent a year improving that prototype considerably. There are a number of reasons and they are all covered above. Circuit, power supply topology, coupling methodology, inductance of one form or another between every tube plate and their power supply. Real world modern production tubes, with many NOS versions available. It all sums up. What you hear is what you don't hear... various sorts of subtle distortion from other topologies that give amps a certain grayness. Trust me, I have heard a LOT of other amps. You don't even realize that it is there until it is gone. That is what these amps sound like. Or don't sound like.... Been a fun journey with Lynn, working out real world builds of the amp and preamp circuits. If you can come to Seattle, please hear them and give your opinion! |
This is getting dangerously close to an infommercial😉 Really, I have enjoyed the thread and never expected it to have this sort of life. I just received the final version of the preamp output transformers from Dave Geren at Cinemag yesterday and installed them. They are the next level up. I expected a subtle improvement, but I am quite shocked. The prototypes were the best I had heard, but the final version has improvements to the core material to give even more detail and even better bass response. You can hear it right away. These will be in Seattle and again, I hope to get everyone's opinion who can stop by and listen. I will state again that there are many paths to audio nirvana and I would never claim that Lynn and I are on the only true path. For those who love SETs please come hear these amps and let us know what you think. You may be surprised. My own personal bias (pun intended) is towards an all tube system. I can hear any solid state device in the signal path and don't like it. Yes, my Lampizator Pacific DAC has a solid state chip set doing the DAC part of the job, but that feeds the output tube grids directly and from that DAC chip set to the speaker is all tubes. I would always choose a tube friendly speaker so that I can use a tube amp. I realize there are those folks who love speakers that are difficult loads and require big solid state amps to drive them. So be it. There is no right or wrong. There is what we like. If you can visit the Pacific Audio Fest in Seattle you will hear the sort of system I favor. All tubes, these amps and preamp, and some wonderful all passive open baffle speakers from Spatial Audio Labs. There will be no DSP or powered subs or anything like that in the signal path. The only solid state device in the chain will be the DAC portion of the Lampizator Pacific, then it is all tubes and passive speakers. We hope you like it! |
To simplify.. All tubes have distortion. The higher orders are what are like fingernails on a blackboard to your ear. DHTs have lower levels of higher order distortion than other types of tubes, and good indirectly heated octals like the 6SN7 and 6V6 are reasonable regarding distortion in the higher harmonics. When I rebuilt a ton of vintage tube gear I instantly could hear that pieces using small signal tubes, particularly the 12au7 were not very good. If you see a 12au7 in a piece of gear other than a tuner, go buy something else. I always preferred amps with octal tubes as drivers. Anyway, to keep upper harmonic distortion down we choose a great DHT, the 300b for the output tube. Traditional feedback approaches can keep higher order distortion down, but phase split circuits and the usual coupling methods, and the feedback itself rob the amp of clarity. Push pull amps have lower levels of distortion. Class A is the way to go. If you can build an amp with no feedback at all and solve all the problems it will sound cleaner and clearer. The driver stage has to be able to really push a 300b. There are numerous forms of coupling, but interstage transformers (if really well made and designed for the circuit) solve a lot of problems. Recovery around clipping is really important for the driver stage and the transformer coupling aids that considerably over traditional RC coupling. LC coupling sounds very good for an input stage where an interstage transformer would have to deal with the higher impedance of the input tube. Power supply topology and design is critical and the output stage should be isolated from the input and driver stages. Of course the quality of the output transformers is a key as well as the power transformer, which should have good regulation. I am sure I am leaving some things out, but those are some key points of the design. |
No, sorry. The 2A3 is 2.5 V filament and 300V plate max. The 300b is 5V and the plates are at about 395 V in this amp. Not ever going to happen. What you have to realize is the 300b is a better tube for this purpose and people who make comparisons may not be doing it in amps where the 300b is actually driven by a driven section that can show what it can do. The best 300b I have heard in the amp is the Linlai WE300b exact copy. It is just superb and can be had for under $800 per matched quad. The "new" WE300b is $1500 per pair. I have not heard them, and at that price I probably won't when I can get a quad of absolutely superb tubes for half of that. These amps deliver about 27 watts/ch and can drive most rational speaker loads. A 2A3 amp would be limited to more efficient speakers. That may work for some, but we wanted an amp that could drive a much wider variety of speakers. |
I am not sure the of the adjective @whitestix would use to describe the amps, but "trippy" is pretty much spot on. It is funny, because when I first wrote Lynn after building the initial stereo version with the CCS on each 6V6 plate I told him that it was so clean and clear and threw such a soundstage that it sounded like you were high every time you listened to it. He was amused and wrote back and said that he and Karna described the sound of the first amps as "trippy". That indeed is how they sound. They are unlike anything I have ever heard, and with each improvement, they get "trippier". Adding the Raven preamp with XLR connection directly to the input tube grids pushed them to new "highs" 😉 I have an old timber frame house and the ceiling slopes upward from about 10 ft at the speakers to at least 20 ft overhead at the listening position. So there are no ceiling reflections. The sound stage is huge, and as I said earlier, it is akin to Omnimax theater for the ears. Sometimes you are sitting inside the recording if that makes any sense. Trippy indeed, and once you hear it, you just cannot unhear it and go back to some other amp. It sort of blows the lid off of things. |
@markusthenaimnut I have no idea. I think Lukasz at Lampizator was. Yes they will be pricey because the power supply topology is something that I have not seen in any commercial amps that I haven't built, and there are custom wound transformers throughout. So even if someone would build a similar concept, these have a lot of features that probably wouldn't be in something else. Hence the cost..... Again, this was essentially a cost no object (within reason) project to see what was sonically possible. I am pleased with the outcome. There are certainly many decent quality tube amps out there for under $5,000 including the Kootenay that I used to build. None of them are this good though. Doesn't mean you cannot have a really satisfying and enjoyable stereo for less. Just that if you want this level of performance it costs this much to do correctly. |
Link not working, no. There are some monos on ebay with no tubes for $2-3K per pair. SE amps. Typical Chinese amp in that you have no idea what is inside that transformer box. Could be ok, could be $99 transformers. A tube amp is the sum of three things. How good is the circuit? How good is the power supply? How good is the iron (transformers)? The circuit might be a faithful reproduction, the power supply and iron are suspect. Ali Express brings to mind two words: caveat emptor🙄 |
The speakers appear to be 8 ohm 90 dB from a stereophile review. They dip to 3.2 ohms, which isn't bad. The amps would drive them with no trouble in any reasonable sized room. I cannot comment on pricing until Spatial Audio figures out all of their costs. I would expect $15,000 - 20,000 per pair with premium tubes, but that might be off a bit. There will be an announcement after the Seattle show in the spatial audio lab website once it is all figured out. |
As Lynn said, the amps have dual regulated supplies, one for the 300b and one for the input and driver tubes. IF the specs on that KEF speaker above are really what the review said, then the amp would drive them. Also, as I said far above somewhere, the first stereo prototype of this circuit with only one power supply per channel drove a pair of experimental Spatial Audio Labs X4 prototype speakers that were approximately 87 dB 4 ohm to insane levels, much as what Thom was describing above. The monos have dual supplies in each amp, so would be even more capable. All that said, I would stick to speakers that are 88+ dB and very well behaved. The spatial audio X4 current model is 88 dB 4 ohm (and very well behaved) and the amps will happily drive them to ear splitting levels in reasonable room. |
"There are now class D amplifiers that have a distortion spectra that if you had one on the bench you would be completely convinced you were measuring a really well-behaved triode tube amplifier." Maybe. Except that there are things we cannot measure. I prefer the sound of a good tube to any SS device I have heard to date. Personal preference. I would not be at all surprised if that Class D amp measures better than my tube amp in every regard. I bet in a blindfold test I would choose to listen to the tube amp. Again, personal preference. Other people would make other choices, as it should be. |
These amps are still prototypes and being tuned as we speak. So what Cloud wrote was in reference to the first prototype a year ago. Spatial Audio Lab had that amp for maybe 6 months. The mono amps are probably 25-30% better at least. @whitestix has a pair, and Lynn and I are still tuning them and have improved them since that pair went out. What will be shown at the Pacific Audio Fest in Seattle will be very close to the final circuit, but there will probably still be a bit of tweaking after that. I would expect production and sales to be Q4 of this year and maybe Q1 of next. We have to see how it goes. Again, I hope lots of people can hear them in Seattle and give an honest opinion. They will come to market, I promise, but we want them to sound as good as they can first. |
@pindac Exactly my friend, exactly. Once the power supply is right, all the operating points are right and there is some serious listening, then the tuning begins. We are almost there... |
I agree with Lynn in that I won’t work with power supplies over 550-600V. The teflon mil spec wire is all rated at 600-630V so you would have to source 1200V wire for headroom. All normal parts are rated at 630V so you would have to source special caps, resistors, etc... You don’t mess around with 1000V or you will have a fire. Also the transformer set in these mono amps including the custom interstage transformers and choke would eat up most of your budget. I like some Lundahl iron, but I found that their IT started ringing above 15KHz in my circuit, so you would most likely have to get custom iron to do your project as I did. So yes, you could certainly build the project you discuss, but it isn’t simple, there are lots of issues and sourcing of custom parts rated for 1kV and if you use Edcor or Hammond iron you or something else of that ilk you will get medium grade amp, not one that has incredible detail and sounds alive. So if you build that amp with $2000 worth of parts you may be able to do it, but if you spend a lot more you will get a much better amplifier. You will still have a fire risk if you don’t make sure every single part in there that sees high voltage is running at no more that 70-75% of its rating. Easy to do at 500V, but a lot harder at 1000V. |
Hi I am sorry, but I am not giving anything about the design of the amp away. I had ITs custom wound for the project. My amp is PP, but if you need a load resistor with your circuit then I would try two kinds. A good quality wirewound of sufficient rating, and a good old Kiwame 2W or 5W depending on what you need. I usually use wirewounds, and not cheap ones, but Ohmite or Vishay or something else of quality. Which you prefer will depend on the circuit, your ear, and the Hashimoto iron. The resistors are cheap so try both kinds and see what you think. |