erik2A3

Easy to read bold-face type - thanks! Atma-Sphere Is just one example -- the main point had to do with the need for an output transformer, which OTL amps don't require. Let me provide another example related to the output impedance question, if that would help: Paralleling of output tubes, whether single ended or push-pull parallel has been done for many years by skilled designers. We would likely agree that whether the practice should be avoided or not is, in my opinion, probably rather dependent on who one asks. http://www.transcendentsound.com/Transcendent/Mini_Beast.html Or the Atma-sphere Novacron http://www.atma-sphere.com/Products/#Novacron And the last example here on this from me - very high power output transformerless amplifier again from Transcendent Sound with an a vanishingly low output impedance, and easily capable of driving 4 ohm loads: http://www.transcendentsound.com/Transcendent/Transcendent_Sound_BEAST_OTL_Tube_Amp.html

And I would also give Maynard's amp a strong vote -- based on the fact that he is someone with extensive experience and excellent wiring skills.

A number of forum members have various incarnations of the fairly common singlended 12ax7/el84 combination. I have also built a version to use with Klipschorns and our Lowther rear-loaded horns (106dB/watt). I had a friend who purchased this amplifier and liked it. It's approx 4 watts output can drive a pair of La Scalas quite satifactorily, with of course the usual caveats. For the cost, a decent introduction to single-ended class A amplification. I have purchased tubes from Tube Depot many times, and have been very pleased with their customer service. They also offer kit products that would be fun for someone interested in a little DIYing https://www.tubedepot.com/products/tubecube-7-stereo-vacuum-tube-amplifier

And of course there are those designers -- Atma-Sphere, Tenor Audio, Transcendent Sound, and others, who view output transformers in general as a part best avoided completely. Check the bandwidth and power specs on this amplifier from Atma-Sphere (these are very highly regarded amplifiers), and then note that it not only does NOT use a small output transformer, it uses no output transformer, period. In a conventional (transformer coupled output) an OPT is needed for impedance matching between the very high plate impedances of output tubes (either push-pull or single-ended) and the much lower impedance of a loudspeaker voice coil. As in the case of those designers mentioned above, an ouput transformer is viewed as something of a necessary compromise - transformer-coupled amplifiers MUST use them in order to be capable of effective power transfer into a loudspeaker load. And so, we hear of builders and/or designers throwing out terms like "heavy iron" with a certain admiration. And that's fine; in some cases and in some circuits "heavier iron" may be a benefit, but in my view not necessarily so. Another criticism has to do with damping factor and generally higher output impedance associated with transformer coupling. In this, OTLs (amplifiers that designed to NOT require ouput transformers) can have an arguable advantage. Here's an OTL from Atma-Sphere: http://www.atma-sphere.com/Products/ An example of a neatly wired and dressed amp, also from Atma-Sphere: fun to watch http://www.atma-sphere.com

Maynard - indeed! I also have a couple of amps with transformers and chokes that could do double duty as boat anchors! I had once mentioned some of the benefits of the antique (but fairly recently revisited) output technique known as 'parallel feed' (which many know more commonly as para-feed). What is different about parafeed is that the OPT handles audio, only, and where the output stage B+ supply is delivered by way of a separate and large plate choke. As such, the output transformer is considerably smaller than the more conventional output transformers with which most are familiar. Some members commented that such an amp would be incapable of any appreciable low end response because of the much smaller (and visually less impressive) size of the output transformer. Such a mindset is unfortunate, because parallel-feed (also known as shunt-feed) can sound stunningly good and can have absolutely superb bass response. I have also known those who (to no fault of there own -- they just didn't know better) thought that power (as in wattage) had a direct correlation with the size of output stage tubes (or tube): the larger the tube, the more powerful it would be. Thank you for sharing your knowledge and experiences!

Kevin mentioned Decware above: a couple of years ago my amazing wife bought me a Decware Mini Torii for Christmas. It's a fascinating little amplifier, and one might (ignorantly and unfortunately) dismiss the single-ended use of a 6V6 as rather mundane. This little amp makes a very clear case for the potentially very high sound quality of such a common valve in the right circuit -- and that output transformers do NOT need to be the size of welding machines to achieve very respectable low end response. It is the amplifier I'm using right now with our La Scalas, sans preamplifier (which I like to avoid when possible).

I'm glad you're still enjoying those Wolfram. I really liked your DRDs when they were here. BTW: what midrange horns are you now using with the Klipschorns? I remember you had been doing quite a bit of experimentation with them.

Mkane - what a great looking room that is!

Thanks The Star Chief is also a DRD circuit with regulated B+ supply. I remember Jack Eliano's description of it with the first DRD 300B circuit he published in VTV magazine -- where each section shakes hands with the other. Very much the case with this as well. The DRDs, including the 2a3 version I built from scratch lots of years ago, are the most hum-free and quiet AC heated SET amps I have ever heard. Really, really good sounding amplifiers.

Kevin - would you explain the basic circuit design of the Star Chief compared to that of the DRD 45? I'm very familiar with the direct reactance drive circuit; what is different about the Star Chief monoblocks in terms of input/driver and output stages?

Doubtless there are those that will dutifully shrug a shoulder at such small power. If that's the case, such a mindset might find the so-called Transcendent Sound 'Beast' more to his or her liking: 120 OTL watts into an 8 ohm load. Designing a conventional transformer-coupled amp is comparatively straightforward once one has a certain level of understanding and experience under one's belt (or one's hat); designing a quiet, balanced, and reliable high-power OTL is considerably more challenging. There are, of course, other companies that offer OTL amps. Check the price tags on some of them. http://www.transcendentsound.com/Transcendent/Transcendent_Sound_BEAST_OTL_Tube_Amp.html

http://www.transcendentsound.com/Transcendent/Mini_Beast.html The new 4 watt (12 bridged) single-ended SEOTL. As an owner of the first one he designed (and he is someone I know for a fact does NOT think the time for tubes has come and gone -- quite the contrary), I have not heard this newer version, but it apparently reaaly good. Power-wise, the closest in the lineup right now is the 300b OTL, that uses a total of 8 300bs for 1.5 watts/channel. Despite it's similarity to the 45 in terms of power output, it is supposed to be astonishingly good sounding.

Nikolas The primary amplifiers I have used with our former Klipschorns and now La Scalas are single-ended triode designs -- 45, 2a3, and my personal favorite, the 300b (*in the specific circuit in which it's being used). People often comment on the superiority of one tube over the other for a great number reasons, however in my own experience with these specific valves, my impressions are that the circuit/s in which either valve is used has a greater impact in the overall presentation than the tube type. I have compared all three in the same amplifier with minor provisions made in terms of filament voltages and values of output triode cathode resistance. Moreover, my opinion regarding whether either triode is capable of what has been described (and with all due respect to those who chose that descriptive word!) "gargantuan" sound is, at best, both highly personal and subjective. The circuit I have built for my 300b monoblocks is the antithesis of euphonic, warm, tube-like, etc. It is a very fast, clean, and open sound, particulalrly, as mentioned above, in the midrange. This triode also has the advantage of being quite a bit more powerful (again in relative terms) to the other two. The 45, in my opinion, has a similar mid-range quality, but to me sounds a bit threadbare in the lower registers; very likely simply due to its comparatively lower power. As Kevin mentioned in relation to his new Oris Horns, it is or course possible to augment the low end response with a dedicated and more powerful amplifier -- even incorporating with what is often derisively referred to here as 'fool's bi-amping.' With some experimentation and the right amplifier, this can actually sound extremely acceptable. Trust your own ears; we all have differing levels of hearing acuity, not to mention likely different ideas of what sounds good or gargantuanly loud. In terms of loudness, the 2a3 (in OUR listening space) is capable of very loud and clean SPLs -- but I would remind that my impression of very loud is almost certainly different from those of others. I also use the 300b via the 4 ohm secondary tap on the output transformers, which to me gives just a slightly tighter-sounding bass response. Let me suggest another option that may be the best of both worlds: OTL. Output-transformer-less amplifiers, particulalrly the ones I have from Transcendent sound: www.transcendentsound.com , have an absolutely stunning low-end response and capability --'one that is immediately obvious and decidedly different from the transformer coupled triodes mentioned above. An output transformer is needed on most tube designs in order to match the low impedance loudspeaker voice coils to the much higher impedances associated with output stage tubes, and do so, as many OTL users and designers may think, at a sonic compromise. Again! I say this with the qualification that everyone is different and a universally correct approach simply does not exist. The Teanscendent Sound line-up is completely different from what it was a decade ago, and in fact includes a new 300b design. You have many options! I remember years ago, when there was a specific class A transistor amp that a number of people were discussing in very positive terms on this forum. I had the opportunity to listen to this amplifier in our system at length, and, try as I might, could not reconcile myself to the fact that yes, it gave an exceedingly nice low end response, but to me sounded not only dry and sheer in the midrange and treble regions, but flat in terms of layering of instruments and portrayal of notes. And once more: an example of my own highly personal and subjective interpretation. Others liked the amp very much! It just had nothing on the 2a3 in terms of transparency and tone.

For LOMC On another table I'm using this-------> http://www.raysamuelsaudio.com/products/f-117 A small but very capable performer. Features dual mono adjustable loading (impedance only) and variable gain. Obviously extremely quiet operation. Used for MM, the Samuels is really good too; to my ears possessing a slightly tighter or more highly damped sound compared the the Transcendent Sound phono stage (which just a blast -- very lively, excellent retrieval of detail, punchy bass).

Transcendent Sound is an excellent MM phono stage -- have one I use often.

Do as djk suggests. with an isolation transformer. They are extremely effective. There are some here who know what they are talking about; he is one of them. 3-to-2 prong cheater plugs are great as diagnostic tools, but IMO perhaps not the best choice for a permanent solution for breaking a ground loop. Break down of power transformer insulation and/or other wiring on the AC side of power supplies in modern equipment is highly unlikely, but it's really not a bad idea to maintain a safety path to ground in the improbable (but not impossible) event of a suddenly "live" chassis. It can and has happened.

Wolfram - Certainly I know of Cabasse! I've read MANY reviews about them over the years; always very positive too. Funny you mention Tannoy: the Tannoy Glenair is a loudspeaker I may pursue seriously sometime when (and if) I have the means. The dual concentric drivers have been around for a long, long time; and the build quality of the big Tannoys -- basket, motor structure, and so forth is really superb. We are doing well, listening mostly to vinyl on three separate systems. The Lowther horns with PM5A drivers -- not a single capacitive and/or inductive filter to speak of. Driver surrounds and spiders are still loosening up even after many hours, but they sound really nice, and are slighltly more efficient than the La Scalas.

Hi, Wolfram! A very good friend, a classical pianist, adores his Quads. Hoping you are well, Erik

The old days were pretty amazing....whew. Edit: I think I fled the last time at about 7,000 posts....LOL!

Jim Thank YOU for your comments! Some of the most astute listeners I know are people who, first and foremost, are serious music connoisseurs. I have a friend who is not just a good classical pianist, but an exceedingly talented one. He knows virtually nothing about audio electronics and the science of acoustics, but is someone in whom I have great trust in terms of critical listening. I will say here, too, that he does NOT care for horn speakers, describing them as far too harsh and forward-sounding. His speakers are vintage Quads and a pair of small, very high quality two-way monitors. I know a bit about audio electronics -- enough to know that I have a huge amount still to learn. I know what brands of capacitors and resistors encourage the quality of reproduced sound I generally prefer, and I can read both crossover schematics, as well as those of rather more complex amplifiers and radios. But I would be the very last person to say that the possession of such knowledge automatically also gives me the qualification or right to inform others about what they should or shouldn't like or do. I enjoyed your post this morning!

Dave "...people who have no ability to discern quality or truth." I have known you a long time on this forum (which I joined in 2002, I think it was) and don't recall many statements like that from you. As a (quite satisfied and happy) owner of a pair Bose 901s, then I suspect I am guilty as charged. Argument can be fascinating and a thoroughly rewarding means of sharing differing opinions about.....anything: philosophy, art, food, genres of music, personal preferences in audio equipment, and in my view is so much more, how shall I say...effective, I suppose, when done in the absence of overtly informing participants of their inadequacies. Our primary system, essentially two separate systems, consists of a pair of split La Scalas and a tall pair of back-loaded horn cabinets with single, wide-band drivers -- Lowther PM5As to be specific. Our sources are predominantly vinyl, by way of VPI and Clearaudio turntables with, respectively, cartridges from Audio Technica and Dynavector. Amplification and preamplification consists of pieces I have built myself or completely taken apart comprehensively restored to factory specs using factory schematics. The Lowthers are 100% crossover free, and the type AL network that came with the LSs was replaced by me with a more common lower order Klipsch network -- despite the fact the midrange horn drivers are the K55Ms. I like a hot midrange. The La Scalas are, generally speaking, in the corners of the room, though not tightly, and are about 15' apart. The Lowther horn cabinets are to the inner sides of the La Scalas. The long wall of the room is roughly 21 feet. As you know, the La Scalas, as most klipsch speakers, present a very fast and open sound with often startling clarity. Dynamic contrasts are equally engrossing. We call this area of the house the "listening room." It is upstairs on an (unfortunately) suspended floor, with damping materials beneath the cabinets to minimize energizing the floor as much as possible. Regardless of these profilactic measures, the system is not totally immune from said vibrations, and there remains a small amount of I sometimes refer to as a "music box effect." We use an SVS subwoofer for everything below about 80 CPS. But we also spend tons of times downstairs...cooking, talking, listening to the news, listening to music. I once broke the above system down in order to have one or the other loudspeaker systems in this downstairs living area and....both the a Lowthers and La Scalas, despite my (alleged) inability to discern quality, just sounded BAD. Regardless of much experimentation with positioning and repositioning (and these are NOT small or light-weight cabinets), I could not get them to load the room the way they did so much better upstairs. Our living room is a very unfriendly room for conventional, two channel music listening. When I say conventional, I am referring to forward (only) radiation from speakers. Pondering some possible solutions, I remembered the 901s I auditioned once just for fun -- to see what all the fuss (both negative and positive) was about. So, I thought to myself, instead of fighting room modes and awkward interior spaces, maybe I should try using the surrounding walls ACTIVELY instead of fighting them. I also remembered the many band and orchestra performances I've been to where huge sound reflectors were used BEHIND the musicians, and how stunningly good it sounded in those venues. One of Dr. Bose's premises, and the one upon which the 901 was conceived and built, was that the majority of acoustic energy produced by a large collection of musical instruments is radiated not to the front, but to the rear. Thus the use of the giant reflectors I mentioned, and thus the installation of a number of smaller drivers in the BACK of the 901 vs the single forward front-facing driver. The 901 is NOT, by the way, intended to be used without it's requisite equalizer; which, I should add, is a line level component. They do not use passive resistors, capacitors, and inductors for frequency division between the drivers, nor do they use Zobel equalization networks, resonant peak filters, notch filters, and so forth (which I don't care for) Does the need for an equalizer necessarily invalidate the 901s as potentially great transducers? I don't know, what would be the result of removing the crossover and required corner placement of the Klipschorn? The Klipschorn is capable of pin-point imaging and focus, as well as what was arguably the most palpable, tangible, and realistic reproduction of music I have heard. However, nothing is settled. The Klipschorn, as I learned from first-hand experience when I owned them, has certain rather specific requirements to sound their best. To simply recommend them out-of-hand as the be-all, end all (which for some might very well be the case), is advice worthy of consideration in terms of weighing not only the pros but also the cons. Our upstairs long wall, wich as I said is roughly 21 feet long, also fortunately has two ideal corners for K-horns. On that wall, they were able to plant a singer, saxophone, or solo guitar center stage with really uncanny precision. Although stereo imaging is not necessarily a primary concern for me, the Klipschorn was extraordinary in this respect. Put the same speakers too close together or in a room not well suited to their idiosyncrasies, and it becomes much more difficult to describe them in the same glowing and positive light. The success or lack thereof of an audio system, which is essentially a machine of sorts, is arguably very context dependent. In fact, I consider the listener to be very much one of the 'components' of the system as a whole; and the human inconsistencies and variabilities we all experience from time to time in terms of overall health (which may impact hearing acuity), changes in mood, and so on, can all come into play with our perceptions of reproduced music. I clearly recall cases where a forum member one day had expressed great satisfaction with the sound at which he or she had arrive, only to make an about-face the following day and say something such as, "I came home from work today, turned on the system, flopped down a record.....and everything just sounded WRONG." Without something to power them, the most expensive and best speakers in the world are useless. The system without a listener simply does not exist. One solution to the lack-of-corners-for-Klipschorns syndrome, as we know, has been the construction of false corners. But again, like the Equalizer to the 901, does the possible need for such a construction project in order to make the best use of what might have been a financially difficult investment make the otherwise steller Klipschorn a lousy speaker? My wife and I talked about this for awhile, and, based on some of the reasons mentioned above, decided to try the 901s. With the choices we have at our disposal, the 901s have been the single best sounding system we have used in this particular area of the house in the fifteen years we have been here. However, they sounded horrible with ALL of the valve amps I tried. The best combination has been with the Prima Luna Prologue III preamp I bought used and repaired and 110 solid state watts per side in front of them. And to the original OP: I extend a sincere apology for even mentioning the Bose 901s. I agree with you that vintage La Scalas (or Klispchorns under the right conditions) can be just killer speakers. I love ours and won't make the mistake of selling them as I did the first pair we had. Enjoy!

Agreed, La Scalas are outstanding. Some here have thought the big Heritage midrange horns tear one's ears off, as I remember some saying in years gone by.... A larger number of smaller cones is not at all necessarily more prone distortion (I would think both Bose himself and current Bose engineers would be rather aware of the distortion characteristics of this loudspeaker -- don't you think?) The amount of power the 901s can handle without distortion is considerable. There is a major British Hi Fi publication to which I subscribe that reviews vintage gear often, and in one issue devoted a fair amount of space to the 901s. It quite honestly was very favorably reviewed. But of course they are wrong about what they heard and the traits of the speaker they enjoyed. I loved the Khorns we had for a few years, and in fact miss them very much at times. And yes, there are those who really dislike Bose products (or at least say they do) including the now quite old 901. But guess what? I have been asked by other very serious listeners and audio enthusiasts how and why I could possibly enjoy such ear-splittingly harsh speakers as Klipschorns and La Scalas. And so it goes.

Ah, yes....Bose comparisons... We have tossed that company name around quite a bit since I joined this forum in 2002. I have owned Klipschorns, two pair of La Scalas, multiple pairs of Heresies, and am presently using split industrial La Scalas and back loaded wide-band horns with Lowther PM5A drivers that alone are in the price range of $2,500/pair for the driver alone. Both the a Klipsch and Lowther systems are driven by a number of single-ended and push-pull tube amps which I built or or completely rebuilt. Primary vinyl based systems with, respectively, a Clearaudio Performance SE and VPI Scout decks. Like most horn systems, we enjoy that very immediate, hair trigger sensitivty that provides such instantaneous transient ability and laser-precision imaging. To this, I unhesitatingly add that we also have a Bose 901 series VI system, driven by a large transistor amp and valve preamp. The turntable is a Technics SL-1210 MKIV. I am someone who listens almost exclusively to both modern and classical jazz and classical genres, though I do enjoy a dose of King Crimson, Audio Slave, Tool, Dream Theatre, Genesis (particulalrly Peter Gabriel era), and so forth. I am on my 50s; have played drums and percussion in both rock/fusion and small jazz ensembles, and recently had my hearing tested. I am still able to hear out to the mid to upper teens K-Hertz. Based on sound quality potential alone, and when properly setup, the Bose 901s with good ancillary equipment can produce an astonishingly realastic presentation, with imaging that is every bit as good as the much larger horn based systems above. They are also capable of low-end response that easily betters both our La Scalas (which I like equally well but for other reasons) and Lowther horns (which have a sensitivity of about 106 dBs/watt). Their high end response is capable of extremely clear and open sound, particularly with plucked guitar, bell work on cymbal, snare drum transients, and so on. The convenient though rather disparaging rhyme "No highs, no lows, must be Bose" is arguably inaccurate.

Mark The main reason I was on the lookout for a pair of split la Scalas had to do with my interest in using the bass bin with the Lowthers. A pair became available within a thirty minute drive, and I bought them for $1,000. Once setup, I liked the sound so much on their own, that I just sort of stopped thinking about the Lowther open baffle arrangement. But one Saturday afternoon, after doing some on-line reading about OBs, I decided then and there to give it a shot; and within about two hours had the Lowther's removed from their rear-loaded horn cabs and mounted on the MDF panels mentioned above. The 300Hz crossover is just an estimate that's very roughly based on the size of the panel I'm using, which is a bit smaller than the large OB shown on the Lowther America site. I wanted to run the Lowther full-range, with only a low-pass inductor on the woofer, and the value of the iron core choke I happened to have on hand would work ok in that frequency range. My guess is that the actual Lowther roll-off point was in the mid 200cps. This was of course just a quickly done experiment to give me a general idea of how the Lowther would work in an OB configuration. They did not have the same sense of image focus as when they are in their enclosures, but the very clear and open, and the manner in which the room was loaded (with the driver radiating from both the front and the back) was captivating. There are actually a few OB systems I have seen on the market that were well received, as well as from smaller companies, one of which is Hawthorne Audio.---------> http://hawthorneaudio.us

There are quite a few people using open baffles. Along with our split la Scalas, we also use a rear-loaded horn system that uses Lowther PM5A drivers. The PM5A, which is the second most powerful alnico-based driver from Lowther, is absolutely fantastic in an OB configuration. I had contemplated OB loading with Lowthers many years ago, and mentioned here on the forum an idea I had to...and this is going to sound crazy...mount the Lowther to the back of a toilet seat cover (a new one!!!) so that I could quickly and easily experiment with degree of slant. The problem with this is that acoustic roll-off would be at such high frequency that it would be difficult to achieve a good integration with the La Scala bass bin. So, I made a larger panel out of MDF so that the Lowther would begin to drop out in the range of about 300Hz. I used just a single low-pass choke in series with the LS bass bin, and drove it with a 50 watt SS integrated amp so I could match the gain of the Lowther driver (which in this particular setup would have an efficiency of about 98dB). It is very difficult to find a woofer fast enough to keep pace with the hair-trigger Lowther full-range drivers, but people have had good success using Klipsch bass bins from both the Klipschorn (which I have also used with Lowthers) and La Scala. In my case, the best sound I got with the la Scala was with the dog house turned around, facing the wall behind the speakers, and wired out-of-phase with the OB mounted main driver. I have not had many, as they sometimes say, 'jaw-dropping' audio moments over the years, but I have had a few; and the sound from this arrangement was certainly one of them. The overall presentation was not one where image focus was a dominant characteristic. The sound was similar in respect to some large Martin Logan ESLs I once heard. Transient information was instantaneous and very clear, and the la Scala provided clean tight lower mid-bass response that was far better than the Lowther alone in its big back-loaded horn. I have the OBs I made tucked away for now in a closet......remembering how they sounded as I write this makes it very tempting to set it up again. Lowther America, the primary Lowther distributor in the U.S. has been using OB systems for the English drivers almost exclusively for the past several years. They are a NOT inexpensive drivers, but are extremely good. Nelson Pass is very much a Lowther OB officionado, and has done extensive experimentation with them. If so inclined, have a look here: http://www.lowther-america.com/page2/page12/page12.html And here: http://www.tnt-audio.com/shows/burning_amp2012_e.html