Check out Audio Note Kits website. I know they make a parallel 300b.
300B Tube Amps with 15/16 Watts Per Channel?
Felix Audio makes the dual 300B amp "Lybra"--are there any other manufacturers of that gear?.Does anyone have experience using two each 300B tube amps modified to be two monoblocks with 15/16 watts output power each? If yes, did you hear any difference in the exquisite 300B sound other than more power? All experiences and thoughts appreciated. (Yes, expense is already noted)
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If you don't mind assembling a kit, Bottlehead makes a 300B model called the Kaiju that can be configured to work as a 16W monoblock amp. I have the Kaiju configured in stereo mode and am very pleased with its sound quality. I can only imagine that the Kaiju in monoblock form would sound just as good or better, but with more power. Bottlehead kits are very complete with superb instructions, which makes for a relatively easy build. |
Art Audio Diavolo Copper Ref SET. Verdantaudio.com I think it maxes at 13wpc, but you must use the EML 300BXLS. You would need to discuss having the amp wired to the higher voltage psu transformer windings and bias circuit adjustment for that tube to get the higher wattage. The Western Electric 91a Boasts 20wpc with their 300b and special circuit and solid-stage rectification, (I prefer tube rectification for SET), but that 20wpc is at 10% distortion which is an order of magnitude more than necessary to get the 2nd/3rd harmonic distortion which provides the euphonic magic along with that floaty liquidity and palpable midrange and eerie micro-dynamics . I don't do parallel SET (anymore) after owning the ALLNIC (Quad-Parallel 300bxls monoblocks which will give you 60wpc, but only by using quad-pairs of eml 300bxls (KR AUDIO BXLS MAY ALSO WORK). $25k New or $10k-15k used and theg are made in S.Korea). I don’t recommend parallel-set because it’s not as pure sounding lacking some magic (though better than pushpull or ultra-linear or the phony triode-mode by disabling 2 stages using a pentode) , very expensive, it’s a class A amp with massive heat output aka a space-heater, retubing is way more expensive especially for EML or KR 300bxls. I’ve done all of this before. Do you like running the ac in winter all the time? i now own a muzishare R100 805 model Don’t be confused the 300b is only a Driver-tube for the 805 triode) It produces a real 50wpc and for the money or 4x the money, I really love it. I run TOTL Psvane Acme 805 ($650-$850 ebay) and its the best bang for my buck ive ever had with a SET AMP. It Drives my Legacy Audio Whispers XDS dual-open-baffle speaker exquisitely . Specifically it drives each speaker’s 4x 7” mid-woofers, and the dual AMT custom midrange and tweeter. The open-baffle 15” bass drivers (humblebrag, all eight of them) are actively powered by 500wpc ICE Class D amplifiers. The speakers are 4ohm 94db.
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Don't listen to @brianlucey 😝, I am struggling to remember if I bought his used pair of Allnic A6000 monoblocks. I could be wrong! This much I will admit: i neglected to mention the model in my previous post, I couldn't be happier with the transaction, great packaging and like new condition, he is correct regarding running two pairs vs quad 300bxls, they are meticulously crafted, and we're very impressive driving anything, but between the heat, retubng expense, and that they were IMHO almost too clean, aiming for superb dynamics trading something in tonal colors, and some delicacy with micro-dynamics. I believe the feedback design might be what caused this. |
I had some 300b PP Zero NFB Mono’s with 20 Watts @ 4 ohms built by Ken Uesugi of Japan and they sound stellar and the price is a STEAL; my inter stage transformers are silver and made my Luxman which are different than the ones show in the link below: https://otomon.net/products/detail/72 I have been using mines for 11 months and they have been rock solid Wig |
@wig I am looking for 300b Zero NFB amps myself and the Otoman labs amp might be the ticket. Since most in US will be buying blind, could you describe a bit more of your experience with these amps ? What preamp are you pairing with it ? |
Sorry for the delay, issues with getting Agon to load and login. I am a Big proponent of tubes and over the years have owned some of the best SS Class A Amps but they have really not connected me to the music like tube equipment... I have owned a plethora of tube amplifiers and have 2 additional units on hand, 1 is a customized KT88 with 65 Watts and the other another KT88 but Class A @ 12 Watts and 100 Watts A/B. I knew I wanted to eventually try a 300b amp as the possibility of squeezing out 15-20 Watts in PP with Zero NFB was within reach, so I reached back out to Ken Uesugi of Otoman Labs, Japan and he confirmed that he could build me mono’s that would fit my rack and the power requirements I was wanting. Ken had my Mono’s built in about a month and shipped after the holiday rush to minimize shipping damages but they arrived flawlessly and packing and build quality was outstanding... Amps are as quiet as a mouse and they exudes all of the audiophile terminology but it’s without question that these 300b are more transparent yet with warmth than Any KT88 amp I have ever owned and the bass is much tighter and the top end is more refined, detailed and airy. The power supplies and transformers are massive and quality Tango and Luxman iron... My Pre Amp was built my another tube guru designer and builder, Radu Tarta... It’s a 4P1L direct coupled, filament bias, line output transformer coupled pre amp. It has that 2A3/45 tube sound but with more transparency and dynamics. I’m extremely happy with this combo and feel as I’m at a live event each night I sit down to listen 🎶 4P1L Line stage | simplepleasuretubeamps Wig |
For everyone here who is considering a zero feedback 300b amplifier, something you should know which has to do with the loudspeakers you plan to use: http://www.atma-sphere.com/en/resources-paradigms-in-amplifier-design.html The short explanation is this: tube amplifiers with no feedback don’t adhere to the Voltage drive principles of about 99% of all loudspeakers made. That 1% left over are nearly all made by high end audio loudspeaker manufacturers. Zero feedback tube amps try to make constant power with respect to the speaker impedance rather than constant Voltage. This means if you mix the two technologies you’ll get some sort of tonal aberration. In particular if the amp in question is also an SET, plan on having a speaker that is a bit more efficient! This is because all SETs that are zero feedback only have about 20-25% usable power- above that power level distortion causes the amp to sound ’dynamic’. You might think that ’7 Watts is enough’; here’s a tip: Its the mark of the best systems that they do not sound loud even when they are. If a system sounds loud when a sound level pressure meter (available as an app for any phone) shows that it really isn’t, what is happening is distortion is being interpreted by the ear as sound pressure. Put another way, if your speakers are efficient enough that the SET never needs to make more than about 25% of full power you’ll really start to hear the best of what that amp can do. In case there’s any doubt, this is part of why horns were so common in the 1950s and prior. |
@wig appreciate the feedback. The Luxman iron was a custom order in your case ? I don't see it mentioned on their website.
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@atmasphere thanks for the info. Wonderful explanation. Yes, my speakers Cube Audio Nenuphar is a single wide band driver. The manufacturer recommends amps with 0 or low feedback design, which will also have low damping factor. I have gone through some amps, and fine these recommendation matter a lot when it comes to the bass performance. |
@wig well, I have been meaning to try the Qualio IQ. Both Cube and Qualio comes from the same designer Grzegorz. They have a YT channel (Virtual Hifi) and the performance has been stellar. However, I was under the assumption the Qualio would need some amount of power to perform better. Have you spoken to the Qualio folks to see if low wattage 300b amps are a good match ? It would also depend on listening room and how loud you hear but I can't wait to hear your feedback on the Qualios with the Otomon amps. |
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@debjit_g Here are some more things to think about. I’ve worked a lot with such drivers. Here’s a tip: supplement the driver with a subwoofer. If you can, also do something to prevent bass from getting to the driver! You’ll find the mids and highs to be a lot more coherent, especially at higher volume levels (this is due to the very audible effects of Doppler Effect distortion). If the amp you use is an SET, it will benefit quite a lot from not having to reproduce bass as well. SETs really have troubles making bass anyway due to the requirements of the output transformer; it gets technical but in a nutshell this problem stems from the need to prevent distortion caused by the output transformer itself (BTW a PP amp does not have this problem). As a result no SET can make full rated power at 20Hz; if they did the output transformer would be the size of a small refrigerator! This bit could be easily taken care of by the use of a smaller value coupling capacitor in the SET prior to the output section, with the intention of rolling it off at 60Hz or so. We’ve done things like that for our customers before (although we make an entirely different kind of amp known as an OTL)- so it might be worth it to talk to whomever makes the amp you settle on about that. Since your thread title doesn’t seem like you are limiting yourself to an SET, IMO/IME your amplifier investment dollar will be a lot better served by a PP amp and there are PP 300b amps like the excellent Spatial Audio amp designed by Don Sachs. I’ve been investigating SETs since the early 90s; they have quite a few problems which really limit how they can be best used. If you are in a normal room for example, unless your Cube driver is horn loaded, it does not have the efficiency to really show off what an SET can do with the power you ask about in the thread title. Typically high efficiency extended range drivers like the Cube might be 99dB at best (unless horn loaded) and since SETs only have 20-25% usable power, you really only have about 4 Watts to play with. To give that some perspective, my speakers at home are 98dB and 16 Ohms (nearly the same as yours), so very easy to drive, and I’ve found that they need a good 50-100 Watts in an average size room. In this way the amp doesn’t have to work hard at all and due to the extra cleanliness of the sound, its very natural to use more amplifier power. If I put in a lower powered amp like 15 Watts, the fact that it is more strained is immediately apparent compared to the more power amp.
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@atmasphere thanks for all the info. That’s helpful and appreciate taking the time to educate some of us. I don’t think the Cube drivers are horn loaded but they do have a whizzer cone. In EU they are typically paired with Tektron 211 PSET amps at shows and the sound is sublime. I have seen them powered with 3/4 watts 2A3 SET in small rooms but I don’t think that will work in my situation as my room is a open configuration with lot of volume. Have gone through some amps, like FW SIT3, Pass X25, LTA UL and some other Class D but in all cases it seemed to lack dynamics until I paired it with a LM 805IA. This integrated is also heavy modified and it sounded very good but the only issue is this amp is easily prone to noise and ground loop issues. So in my experience, this speaker needs some bit of power depending on the room situation. I am now trying to see where can I go next. I know for sure getting a Tektron PSET would be an end game for this speakers, so I am trying to explore other options like Otomon which apparently seems very nice as well.
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@debjit_g There is an old customer of mine who has a prototype pair of the design used for the Blackbird amps that Spatial audio is producing. PP300b and they produce about 24 watts/ch. He has one of the Cube speakers as I recall and the amps drive them with ease. So I am sure a well designed and preferably fully balanced PP 300b would have no problem. |
@donsachs I have no doubt that a 24w/ch PP 300b is more than what I would need. I know Clayton's original Spatial Audio very well as I had their open baffle at sometime. The amp looks beautiful and would love to own them, however, its priced out of my current budget (I have other diy projects lined up on the digital side). On another point, I am not sure how important balanced/unbalanced in my system. I have gone through a plethora of DACs in the past couple of yrs and some do sound slightly better in balanced configuration vs unbalanced. The reason why I bring up DACs is because if you have a unbalanced source, I am not sure how beneficial having balanced downstream is. Moreover, in my system their isn't much difference between the two anyway, it more of splitting hairs and I don't run long interconnects. |
I wasn't really suggesting you buy the Blackbirds, just that if you do the 300b route I really think PP is best IMHO. My system is fully balanced from Pacific 2 through to the amp speaker terminals. It is so quiet that I cannot even tell it is on when idling away. So I like balanced with transformer coupling, but we all have our taste and needs. |
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Only one to buy in my mind for higher powered 300B, the Don Sachs/Lynn Olson Blackbird Monoblocks; manufactured by Spatial Audio Labs. Not cheap at $10,000 each, but it appears the culmination is Don's and Lynn's life's work. I do not own them, as they are not in my current budget, but I am lucky enough to get to hear them now and again in my friend's system. I believe they are 24 WPC? He pairs them with the brilliant Aric Audio Motherlode XL preamp, which I also own |
Yes- if 15 Watts the distortion will be more like 10%.
@debjit_g This is a very common comment about single-ended power amps! Single-ended amps (SET or PSET) seem to have more 'dynamics' because distortion on the leading edges of the transients is interacting with your ear in a particular way- the ear interprets the distortion as loudness because it uses higher ordered harmonics to sense how loud sounds are. Those amps with less 'dynamics' are that way because they are lower distortion. This is why I mentioned that SETs only have about 20-25% usable power. Above that level (generally speaking) the distortion masquerades as 'dynamics'. So if you want to hear them at their best, the speaker needs to be more efficient. You can get around this problem if the SET (or PSET) has feedback, but then you find out that the amp is under powered! This is why I've been recommending something push-pull. A PP 300b amplifier can make about 35 Watts which will be far more satisfying your speakers.
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@vthokie83 Yes, the Blackbirds measure out at about 24 wpc. I know Aric and he builds seriously good tube gear. He is a master craftsman. That said, I wish you could hear the Blackbirds with the matching Raven preamp:) It would be a different experience and I would be very interested in your take on the comparison... |
@vthokie83 Interesting. If you do get the chance then please post your impressions! |
@vthokie83 Just curious. What speakers is your friend driving with the Blackbird 300b amps? Just another data point! |
@yyzsantabarbara A nice move that most tube designers agree on is bypassing the cathode resistor. The tube can behave much better. I don't like the 6DJ8 and its variants; while they are quite linear, they are also very prone to microphonics. The schematic (if accurate) indicates it could really do with a grid resistor on the input stage. Since an EL84 is used, an ultralinear output transformer could also be used, resulting in lower distortion in the output section. I know a number of designers that don't like UL operation but as far as I can make out they are intentionally trying to make more distortion. |
@atmasphere thank you for your guidance. As an amp manufacturer yourself, you have been very helpful with the education. Quiet contrary to many manufacturers who come here mostly to advertise their products. |
We all have different views as manufacturers and that is as it should be. I don't give detailed advice because some of my views will clash with others and that is not what I really want to do on a public forum. I will say from years of experience, that in general, the larger the plate on the tube, the better it sounds to ME, but that is not everyone's view. I will also say, that if you know what you are doing, directly heated tubes are the way to go, but there are problems to solve and therefore they are not for everyone. I will also say that I prefer amps with zero feedback, but @atmasphere and I will diverge there, and that is just fine. I respect his opinion for what he builds. I do agree with him that the 6DJ8 family isn't all that good sounding a tube. Neither is the 12au7 and I never understood why people used them. But we all have our taste. I would still take a well designed push pull amp over a single ended one every day of the week, but again, that is my opinion and take it or leave it. I also favor completely regulated supplies, but others differ in opinion. I am sure if you buy an amplifier you can modify it to improve it, unless you are buying a very expensive and well designed amp that someone has put a lot of time and effort into. One that was designed without the usual budgetary constraints. As a modifier of more cost effective gear you can certainly remove some of those constraints. If there are coupling caps then those are generally modified for personal taste. There are certainly things you can do to power supplies on cheaper gear to improve them, but it depends on whether there is room. Often just bypassing a power supply electrolytic cap with a small film cap of sufficient voltage rating can make a subtle improvement for a few dollars. We used to do all sorts of things to improve vintage gear when rebuilding it. |
@donsachs I wasn't a fan of feedback for a long time. Here are two things for you to consider: the first being that in most amps with feedback, tube or solid state, the feedback node (which might be the cathode of the input tube) distorts the feedback prior to its being able to do its job. In the case of a tube, the tube isn't linear. So using the cathode as an input for the feedback means the feedback signal gets distorted by the tube as it mixes with the incoming audio. So IMD, harmonics and inharmonic noise is generated, literally causing the noise floor of the amp to be composed of that rather than actual noise. Norman Crowhurst wrote about this problem in the 1950s but didn't suggest a solution. However the solution is simple: wrap the feedback around the amp in such a way that it can be mixed with the incoming signal using a resistive divider network at the input of the amp (in the case of a tube amp, at the grid of the input tube rather than using the cathode) so that the feedback signal isn't distorted in the mixing process. IOW, much the same way you see opamps do feedback. One interesting tube preamplifier design that used this idea was made by Leak, called the Point One. Properly refurbished and given a good power supply its quite musical. Of course, to do this effectively you usually have to have more gain that can be used for the feedback. That is why Leak used pentodes but I've seen Fisher circuits that used this idea too using 12AX7s. The second problem is if the amp lacks gain bandwidth product, if you try to use too much feedback, at some frequency in the audio band distortion will rise since the feedback is being decreased on a slope of 20dB/decade. Bruno Putzeys wrote a fine paper about this problem. I'm convinced this causes brightness and harshness. This is a very common problem in amplifier design, although not nearly so now as it was up to about 20 years ago. |
Or you can simply use speakers that will run happily on 10 watts and build a very simple (well not that simple actually if you consider power supplies and transformers, etc..) push pull amp with no feedback that is flat from 20-20K with very low distortion to drive them and be happy:) Using DHTs... to each their own. The problem lies in supporting people that need more than 20-25 watts/ch. If they have made that speaker choice so be it. We all have our paths to audio nirvana.... |
