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.
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.
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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. |
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:) |
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.
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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. |
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. |
@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. |
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. |
Hi @donsachs , Will Spatial be in the Montreal AudioFest on March 22-24 ? |
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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@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.... |
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. |
@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. |
Just heard the first production Raven was completed, and the folks at Spatial Audio in Salt Lake City thought it was a big step up from the Raven preamp at the show. It uses a new Monolith power transformer, a newly designed input transformer, and VR-tube shunt regulators, in addition to the regulator used in the show preamp. Like the show preamp and Don’s previous preamp, it uses a Khozmo volume control with a remote control that adjusts volume and balance, and selects inputs. Tube lineup is a pair of 6SN7’s (one for each channel in balanced mode), a pair of VR150 shunt regulators (one for each channel), and a pair of damper-diode rectifiers. The Raven and Blackbird use standard RCA and XLR interfaces, so they can be used with other components, but they sound their best when used with each other. |
I showed the pix of the Amity (1997) and Karna (2003) amplifiers to emphasize they were developed largely in isolation from the SET community. I found out the hard way that SET practice wasn’t always useful with this approach. Similarly, practice in the traditional push-pull pentode world isn’t always helpful. Don’s build and design experience with the Valhalla and Kootenai has been very useful, showing me what worked, and what didn’t. So there are elements of the Amity, Karna, Valhalla, and Kootenai in the Blackbird. Do they sound like SETs? No, they do not. Do they sound like traditional push-pull pentode amps with feedback? No, they do not. The signal flow and functionality is different. The closest similarity are to some unusual designs of the 1930’s, with the very latest 21st-Century transformers and power supplies. The Blackbird is actually the result of a four-way collaboration ... between Don, myself, the transformer designer, and the power supply designer. |
... 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. |
If it doesn’t say "electrostatic shield" there’s no copper foil between windings. Medical-grade is even better, with primary and secondary on opposite sides of the core. If you want full isolation, in the absence of these features, you need two transformers, one for HV, and another for LV. The name brand doesn’t change the shielding, or lack of it ... that requires copper foil isolation, which is a definite hassle for the transformer builder. I should mention the heaters for the rectifiers do not need isolation. Only the heaters and filaments for audio tubes need isolation. If DC regulation is chosen, a higher secondary voltage than 6.3 volts is needed, since regulators need to throw away a few volts to operate. I should mention not all regulators are the same; you can do a lot better than generic 3-pin regulators. |
Hi @lynn_olson , The Hashimoto PT-100F power transformer that I'm going to use for drivers/input B+ and drivers/input filament. But I'm not sure if it has an electrostatic shielding between HV and LV sections. I can see some strips between high and low voltage windings. But as far as I can see they are made from a kind of cardboard. |
@alexberger The resistor value isn't critical. 50 to 100 Ohms works nicely. As long as both chassis (power supply and amplifier) are tied together and grounded by the power cord, its really not going to matter where that resistor actually is, since it will carry no current under normal circumstances. |
I’m going to use a separate power supply (PS) box for my amp project. It is too big and too heavy for one box. I don’t want a monobloc solution, because it is an integrated amplifier. I have 2 GND. One is a power cord GND (1) and another one a circuit GND (2). GND1 will be connected to PS and main chassis, while GND2 will be connected to GND1 thought resistor. 1. What value of resistor is recommended? 2. In which box GND1 will be connected to GND2 through the resistor? In the PS or the main chassis? |
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Here’s a close-up of the 2003 Karna amplifier, showing one channel of the audio chassis, with the power supply chassis out of sight. These have been my personal amplifiers until I received a pair of Statements about eight months ago. Note the aviation-grade Amphenol connector on the rear of the chassis. All connectors and cables are rated for 1.5 kilovolts, using transmitter-grade coax cables to carry the two separate B+ voltages to the audio chassis. In case you are wondering what all these tubes are doing, the input tube is a 5687 (or 7119), the drivers are old-stock 45’s, the outputs are 300B’s, one pair of VR150’s are for the drivers, and a single VR150 is for the input tube. The single EL34 is a current source that feeds the VR tubes. The four blue-painted cylinders emerging from the chassis are General Electric industrial motor-run capacitors. The Statements and Blackbirds are an update of this over-the-top project. I was doubtful the Karna could ever be manufactured until Don came along, with his lengthy experience making the Valhalla (KT66) and Kootenai (KT88) amplifiers. Not only is it more compact, the new Don Sachs power supplies are an order of magnitude better ... and they didn’t exist in 2003.
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The Statements are the previous versions. I strongly urged Don to use a spacious layout, with all components on a single layer. Easier to build and signal-trace. Don ran with the suggestion and improved it by putting all the power supply components on the right side of the chassis, all the audio circuits on the left, with a shield between the two sections. The wiring for the audio section, in particular, is really simple ... transformers, tube sockets, cathode resistors, and bypass caps. The wire lengths for each half of the circuit are symmetric, while cathode resistors, bypass caps and local grounds go to turret boards next to the tube sockets. The bigger chassis also run cooler, as you might expect, since heat-emitting components are further apart, and the top plate is now 18" wide. The Blackbirds might look big, but they fit just fine on standard racks. Sonically, the Statements and the Blackbirds are pretty close. They are all descendants of the original Karna amps, which date back to 2003. Unlike the Karna amps, the Statements and Blackbirds are on two chassis instead of four, which vastly simplifies grounding. Here’s a picture of Gary Pimm (foreground) and Gary Dahl (background), taken in 2003. The Karna’s have the distinctive blue chassis, and the separate power supply chassis are behind the amplifiers. The AMT-1's are Gary Pimm's speakers.
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Alexberger, the Cinemag input and interstage transformers are under the top plate. These are the third generation of the custom Cinemag transformers we started with. The two Monolith transformers are visible on the rear of the top plate. The other things under the top plate (right side) are the B+ and filament regulators, and the master soft-start circuit, with an external 12V trigger. The point-to-point and turret-board wiring under the audio side (left) is very simple, with only transformers, tube sockets, cathode resistors and bypass caps. No current sources or other gizmos. |
@alexberger Yes, but only at radio frequencies. No shielding at audio frequencies, and for that reason steel is likely a better choice if you're running single-ended. We use aluminum chassis in most of our stuff, but its balanced and so does not need shielding to be quiet. |
Hi @lynn_olson @atmasphere , Thank you for useful information. Does aluminum provides any shielding? I will use an aluminum chassis. There is a beautiful picture of Blackbirds. But I don't see inter-stage transformers. Are they under the hood?
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@alexberger I can confirm everything @lynn_olson mentioned regarding your post in his above. Pay attention to all those issues! Regarding this question which has to do with grounding. You’ll want to ground your chassis if its metal (and if you’re running single-ended, ferrous materials will provide audio-frequency shielding). So the ground connection of the power cord should be tied to the chassis. The audio circuit, if tied directly to chassis, leaves you open to ground loops. To avoid this, lay out your amplifier circuit so all the points that go to ground do so to the power supply (star grounding is nice) without touching the chassis. Grid and cathode connections for each tube section (the ground side of the grid resistor and ground side of the cathode resistor) should be common and use a single wire going to the star ground. This forces noise imposed in that wire to be common mode and so will reduce noise. The spot in the power supply to which you tie your grounds can be a buss tying all the filter cap grounds together. Once you have all the grounds starred together, at that point you need to reference the chassis ground. That can be done several ways: you can use a simple resistor from the audio ground to chassis ground. You can use a pair of rectifiers in parallel, each opposite of the other, with a resistor in parallel with that. This higher impedance is presented to ground currents between chassis and the audio grounds which otherwise set up the ground loop. Be sure to have the input connectors also isolated from ground. Most RCA connectors are supplied with shoulder washers for this purpose. In this way, the chassis can be a relatively quiet shield for the audio circuit. You’ll find the audio circuit to be quieter with this practice. |
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1. If the heater windings are not shielded from the high-voltage B+ windings, switch noise from the B+ section can be capacitively coupled to the low-voltage heater windings. Although indirectly heated tubes have significant isolation from line noise, it is not 100%, so some of that switch-buzz gets through. If you listen closely, you will probably hear it. There are several solutions: A) get a power transformer with electrostatic shielding (copper foil) between HV and LV sections B) go to DC heating with a regulator C) use a separate heater transformer. When none of these are done, yeah, that’s cost-cutting, no matter how fancy the name brand. If swapping the rectifier tubes makes a notable difference in the sound of the amp, there’s something wrong, or not optimal, with the power supply design. 2. Yes, the two grounds must connect together at one point, and only one point, preferably the chassis. There’s an old joke: when two engineers get together, they will come up with three grounding solutions, and all of them will be right. Grounds (and shields) should never float, ever. That’s bad practice and a possible safety hazard. Determining the best connection for the ground or shield usually takes a bit of thought (which is why it’s called engineering). There are whole books on grounding. It is not a trivial subject. Part of the problem is language, because one word covers several things: A) Safety ground B) Current return path for the DC currents that power the tubes or transistors C) Current return path for the AC audio signals going through the circuit D) RF and noise shielding |
Hi @lynn_olson , I have a couple of technical questions: 1. Is it a good idea to feed indirect heated tubes AC filament with a separate dedicated power transformer? In my integrated SET 300B amp input tubes receive relatively low level signal after the input potentiometer. 2. I use interstage transformers and separate PS for driver and input tubes. As a result, I have two separate GNDs: 1st - for output circuit and PS 2nd - for input/driver circuit and PS. Should I connect both these GND together to the amplifier chassis at one point? Or can I leave one of these GND floating? |
Here’s the latest: Don is training the folks in Salt Lake City as we near production. The Raven preamp is the same preamp you heard at the show, while the Blackbird now has KT88 drivers, at twice the power of the 6V6 drivers, with third-generation Cinemag interstage transformers and Monolith output transformers, If you’re wondering who Monolith is, you heard them in the Songer room on the Whammerdyne amplifier. Merry Christmas, Happy Hannukah, and a Happy New Year, to all! |
