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)
I've heard, and really liked, the Charney Companion with the BD3 driver, in a system driven by a SET 300B amp. While this amp does deliver more power than a 45 SET, I know your system can get quite loud while remaining clean. It is hard to say what others feel is loud, and your room size and characteristics do play a part, but, if it sounds good to you don't worry. Even if you exceed 25% of rated power, at peaks, so what? You will not be hurting anything with your setup and your ears will tell you if you are clipping excessively.
That's the tricky bit. The easiest way these days might be to use a sound pressure level app on your phone, once you've calculated how loud 0.75 Watts would be driving your speakers in your room.
The AER drivers are measured at 1 meter. Sound pressure level drops off the the square of the distance, but in an enclosed room not so much due to reflections. The size of the room, the distance the listening position is from the speakers and how lively the room is all make a difference. If an average room you're likely alright if the sound pressure is below 90dB or thereabouts.
@atmasphere said, "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."
How do I know how much power my SET amp is using?
I have a beautiful set of Atmosphere Class D that never give me concern of overdriving them. I also have a Shiny Eyes SET 45 Mesh Tube Amplifier from Radu Tara that I believe is 2 Watts. I use them to drive Charney Audio Companion Excalibur with AER bd-3 drivers (104-106 sens???)
Can I measure (or need to) my output to see if I am staying within the 0.75 Watts to avoid excess distortion?
Thanks and Happy 2025 to all.
As a side, I live in New Orleans and am in ER doc. I worked NYE. I don’t always understand the world, but hope sanity and tolerance prevails in 2025.
I used to fix guitar amps for musician friends. They are pretty simple.... (the amps, not the guitarists!)... except Marshalls, which have many small pcbs and jumpers and inevitably it would be a failed bias pot on the board buried the deepest in the amp. A 3 minute repair that took an hour to get to. The thing was, I could always improve the amps, but they wouldn't want you to. They WANT distortion. So you just replace all the bad lytic caps, and make sure the operating points are where they should be, and put k40 oil caps in where old oil caps have failed, etc.. You can get away with making the power supply a bit stiffer, but that is it. Otherwise the amp is too "clean" for a lot of guys.... So yeah, a Hammond is just fine for a guitar amp....
Hit post too soon.. Great iron, not just good iron. The kind of transformers that give you goosebumps if used in the right circuit. If you use a Hammond, you will never hear what the circuit can do....
@atmasphere I agree on the vintage amp transformers. The citation II amps were legendary and would be flat down to about 8 or 9 Hz at full power. The Sherwoods were generally pretty good as well as the Scotts and Fishers. The Eico stuff can vary. They were definitely built to a price point. The best little EL84 amp I ever heard was the Sherwood. If 10-12 watts/ch was enough, the little Sherwood integrated amp was quite enjoyable to listen to. The Macs and Marantz amps also had very good iron. The little Eicos, Heathkit, and others of that ilk were all over the map for quality of iron. Honestly there are fabulous transformers wound today if you want to work with a winder and spend the money. If you buy an off shelf Hammond, or Edcor or whatever you can certainly build a decent amp, but you will not the get the inner detail you will from a more expensive transformer. You get what you pay for. That is why Chinese amps for $1500-2000 are decent, but not great. Good iron is over $1000 for a stereo amp....
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....
@donsachs I find a mark of the best systems is they don't sound loud even when the are- relaxed at all volumes. On that account, I've found that even with very easy to drive speakers (98dB, 16 Ohms) you tend to use a lot more power than one might think!
But at the same time I've also found that the better the amp is at making clean power, the better its first Watt is, that such an amp can be quite convincing.
These two things might seem opposites of each other but they are not.
I designed a little 5 Watt PP amp about 4 years ago that was meant for my bedroom system, because I couldn't find a compact amp (this one can sit on a sheet of notebook paper with room left over) of the same power that wasn't junk. 5 Watts doesn't seem like much (although for a desktop, bedroom system, headphones or a system with really efficient speakers its plenty), but compared to a 5 Watt SET its quite a lot since it has a lot more usable power and is overall more musical than any SET (for example it doesn't sound 'loud' which many SETs do even though they don't make much power) I've heard. I was finally talked into producing that amp about a year ago.
It uses feedback. But one of its tricks is that it didn't need feedback to sound just fine. I mostly used it because it had too much gain (with only 3 tubes/channel).
There are oodles of 20 to 35 watt push-pull amps from the classical era of the 1950’s through the 1960’s. Most of the "mods" of these amps are nothing more than updating the coupling caps, which is a good idea anyway with an old electronic product.
@lynn_olson I refurbished an Eico EL84-based amp recently. That one didn't have good iron so output power was rolling off at 30Hz and distortion at bass frequencies was high. You do have to be careful about what vintage amp you try to 'renovate', 'update', whatever... many of them are built to a price point since back then, they were manufactured as a commodity so output transformer bass response is a likely candidate for cut corners.
I read something years ago that stuck with my and I have always tried to heed. A really good tube amp is the sum of three things. How good is the circuit, how good is the power supply, and how good is the iron (transformers). Those who favour OTL designs can ignore the iron. Of course there are other factors at play such as how much distortion there is in the tubes chosen, but if you use decent tubes and pay serious attention to the main three points, you should end up with a very nice amplifier.
I rebuilt hundreds upon hundreds of vintage tube amps and preamps before I started making my own. You could tell the good ones before you even started. If there were serious compromises in power supplies or transformers, then no amount of replacing old parts with better modern ones would ever make them great amps. You could tell the great amps from the schematic and quality of parts used.
So my advice is the build the best power supply you can, use the best iron you can, and find a good circuit. I exclusively build push pull amps. I don't build single ended or parallel single ended circuits. I understand there are those who favour such designs. I only use regulated supplies, and I also only use tubes with larger plates, and as many directly heated tubes as I can. Those are my choices based on the main rules above, and moving beyond the "conventional" designs I built for years. The conventional amps I built are very nice, but the latest full balanced circuits are far superior to my ear, and more costly to build.
So my advice on a good 15-20 watt 300b or other amp, is to heed the three main rules, and build a good push pull one. If you can DIY you will save lots of money. There are many great parts from companies like Neurochrome, the Rod Coleman regulators favoured by a pretty large camp, read Barola valves site for some great info...particularly on drivers. There are lots of places you can check out for a DIY 300b project.
There are oodles of 20 to 35 watt push-pull amps from the classical era of the 1950’s through the 1960’s. Most of the "mods" of these amps are nothing more than updating the coupling caps, which is a good idea anyway with an old electronic product.
A much bigger challenge is re-designing the power supply, which usually means a new, roomier chassis without the period charm of the original. The output transformers, though, are often very good and worth retaining. But this does mean the destruction of a desirable vintage amp, which some view as cultural destruction, like ruining a 1956 Chevrolet in good running order. I personally do not approve of destroying vintage equipment in good working order.
But there are plenty of modern amps which take the same approach, using vintage circuits, and with good output transformers (which are NOT cheap, often costing more than an entire Chinese-made amp). I can heartily recommend the Kootenai (KT88) and Valhalla (6L6) amps made by Spatial Audio Labs under license from Don Sachs. They are best classical-circuit amps I have ever heard, superior to any restored vintage amp, and priced very competitively. If you are extremely price sensitive, you can’t go wrong with Quicksilver, which are serious amps, made in the USA, and by a guy who knows what he is doing.
P.S. Building a good PP 300B amplifier is surprisingly expensive. Sure, you can adapt a 1950’s circuit, but a 300B is far harder to drive than an EL34, 6L6, or KT88. The modified 1950’s circuit will have high distortion in the driver portion, which then dominates the sound of the amplifier. This is especially true if 12AT7, 12AU7 or 6DJ8 nine-pin miniature driver tubes are used. Put another way, vintage circuits from the 1950’s or 1960’s, which are designed for beam tetrodes or pentodes, are not well suited for 300B triodes.
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....
I will also say that I prefer amps with zero feedback, but @atmasphereand I will diverge there, and that is just fine.
@donsachsI 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.
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 @atmasphereand 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.
A PP 300b amplifier can make about 35 Watts which will be far more satisfying your speakers.
@atmaspherethank 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.
I was asking him what 300B amp (preferably mono) he would recommend. He came up with this and said it is easy to mod it to make it sound even better.
@yyzsantabarbaraA 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.
My friend is building speakers that can run on 1-watt. I was asking him what 300B amp (preferably mono) he would recommend. He came up with this and said it is easy to mod it to make it sound even better.
Don, I suspect I will get that chance one day.....in the not too distant future. He's already talking about adding the Raven, which I encouraged......but not my money.
@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...
Ref atmasphere's post. It depends on how much distortion one is willing to tolerate. An SE amp with a pair of 300Bs will not put out 15 watts @1%thd.
Yes- if 15 Watts the distortion will be more like 10%.
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
@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.
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
I have a pair of triode labs parallel 300b amps. Made in Japan. I love each system I have for different reasons. The voice is to die for. It is quick and musical base is there but I have other systems that are better in that department
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.
@donsachsI 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.
Some of this fascinating discussion goes over my lumpy bald noggin and I’m not sure I’d want the news a phrenologist might report. I have the Sachs/Olsen 300B mono blocks and thier Pre. No listening fatigue is my truest test and that’s an A+.
@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.
@atmaspherethanks 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.
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.
@debjit_gHere 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.
@wigwell, 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.
I have been using these mono's with Liberty Audio X-VOX, which is a parent company of PBN Audio but they are being replaced with Qualio IQ which will arrive next week 😁
@atmaspherethanks 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.
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.
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
https://simplepleasuretubeamps.com/products/
@wigI 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 ?
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:
I sold my A-6000 for lower wattage single ended triodes - all you describe is regained. Parallel circuits are difficult to engineer and that is the trade off. But the A-6000 is far superior to push-pull - in my exceedingly subjective opinion.
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.
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