Erik Mandaville

Another option is bi-amping (which I admit can be another can-o-worms). I've been auditioning our La Scalas with a combination of single-ended 2A3s or 300Bs on midrange and tweeter, and a very quiet and clean 60 watt (for me this is very serious power!) vintage Hafler SS amp straight into the woofer, series inductor bypassed. Now granted, there are many unquestionable benefits to active biamping with line level crossovers. That fact notwithstanding, I have seen many examples of users very satisfied (where in fact some manufacturers had recommended) doing this passively rather than actively in order to maintain other carefully tuned elements associated with the crossovers -- such as impedance compensation networks, notch filters, and so forth; where if someone were to decide on an active line level system that didn't have those carefully (of course via measurement, but ultimately and finally listening) features, an otherwise carefully configured balance of driver interaction and response would be defeated. There was a thread recently contributed by a forum member who switched from just such a formerly very much enjoyed SET amp to another classic valve amp with much more power (say in the range of 20 to 25 watts, which at the end of the day isn't all that huge) If I remember right, he was very, very pleasantly surprised.

I also agree with Paul and CT, but I also have heard more powerful amplifiers sound spectacular on both our Klipschorns, as well as a recently acquired pair of La Scala LSI (tapered top, split sections, fiberglass, aluminum trim) in really good condition. I've really liked the way the La Scalas sound, but this model is sculptural and sort of industrial-tech looking at the same time. I Got them from a very nice family nearby. I'm using the La Scalas with a Transcendent Sound SEOTL, which I have to say is really among the very best amplifiers I've had. I've looked at Bob's kits many, many times, and they seem to be extremely well thought-out, with very good parts, bullet proof chassis, and also heavy power if needed. As much as I like the lower power single ended amps, they have not been able to quite compete, in my experience, with a bit more muscle in the low end. That's just been my perception and is therefore nothing but an opinion. The SEOTL (OTL = output transformerless) is an exception, however. The control this amplifier has (with about the output power of a 45 triode) in terms of bass response is really iron-fisted, despite it's low power. I have to mention a second system: We recently received a custom-built pair of absolutely stunning new horns from The Horn Shoppe! these little things with a 4" Fostex driver hit so far out of their league it's unreal. And they are so small! Like our big Lowther horns, they need break in time -- the single, full-range (well, maybe not literally -- at least yet) drivers really need time to loosen up and relax. Out of the box they are a little bright for the first few hundred hours. If you can try some different amps, that would be good. That way you can form your own opinion. Have fun! Erik

Bruce Teaching is very alive and doing well -- just on Spring Break which gives me some extra time. I hope you and your wife are doing very well, also. Marie and I and our doggie kiddos are all fine. I think it's great you still have your Moondogs -- me too. They are classics, IMO, and I'll never part with them. Those poor things have undergone so many changes and modifications over the years, that this past summer I completely rewired them back to the original design, and just organized for better presentation inside and out. I found some nice Russion PIO capacitors for coupling that were really reasonable compared to the alternatives, and have been very good, not to mention totally reliable. Military grade things that are heavy for their size and built well. I think Craig mentioned these positively some time ago, as well. Still, there is always that special little grid choke on the 2A3 that I liked so much in the J-F Lessard parallel feed amps I made several years ago. That's the MQ part I mentioned to you. I've found some alternatives to that, but I think the MQ choke is made really well. Very easy mod, too. Good to hear from you, Bruce. Erik

Hi, Jay Great -- this is one of the reasons why I thought you might like this amp over the other one discussed. You get some advantages of indirect heating/slow warm up, which is nice for tubes and makes them live happily. Other than that, what you get is either more or less voltage sag, which might be reflected in certain performance aspects. The only differences I seem to be able to hear with these things has to do with some of the valves being quieter than others, but I just like the idea of slow warm up if possible. Enjoy, Erik

Jay I'm glad you are putting those Winged C 6L6s to some good use, and that the amp has been satisfactory. I have a couple of EH 5U4G rectifiers here that I'm not using. I'll send them to you if you'd like to try them. Of the few I've tried with the 300B monoblocks I built last year, the Svetlana 5U4s have been really nice, quiet, too. One thing to think about if you start experimenting with different rectifier types is the input to filter capacitor value, though particularly in the case of a cap input (which is the first capacitor after the rectifier. If the amp uses a choke input (I honestly can't remember which the Baldwin is) after the rectifier, it's different. Some rectifiers are able to handle much higher input cap values than others, as is the case with the 5AR4. As an example of the opposite, the Mullard GZ37, which I use in my Moondog 2A3s, has a very low recommended value for the input cap -- 4uf, I think, off the top of my head. You can have problems if you use a rectifier designed for very low input capacitance as a substitute where values more in the range of up to say 60uf would be okay. Another thing to think about is the different current draw between these different 5 volt rectifiers. One CAN'T simply plug one in for the other as an acceptable replacement without considering the above. Have fun, Erik

Here's an example: http://www.6moons.com/audioreviews/musicfirst/passive.html

The word "preamp" might also simply be used in terms of its position in the signal chain. Some "passive" line attenuators are transformer-based, with a primary and secondary winding, and can, as in the case of a phono step-up transformer, be configured to offer a bit of gain in addition to signal attenuation. Passive transformer based attenuators, while in most cases (that I've seen) are more expensive than the more common type mentioned above, may subjectively offer improved performance because of arguably better input/output impedance ratios. Most modern sources can, on their own, provide enough gain to push many amplifiers into clipping distortion; which is why some have found passive attenuators, where short interconnect can be used between components, a better solution than an active, power-supply-driven line stage. Try both, choose what you like best, have fun.

Paully: A very honest answer. I recently finished a pair of 300B monoblocks that also incorporate direct coupling, so I have an idea about what you (might) be talking about. The 'tubby' bass said to be sometimes associated with the 300B was not something I experienced, in fact, at least with the Sophia 300Bs I'm using, it's quite the opposite from 'loose' or over-ripe bass response.

This is kind of funny -- not the 2A3-300B conversion, just the fact that the thread is two years old if a day. As if there were no gap in time. Paully: To make this change are you just changing the filament voltage between 2.5 and 5V and leaving the rest of the circuit the same? I really love our SET amps, both the 2A3s and 300Bs. I also can't help but admit to be being very impressed by the sudden and scarily realistic snare and kick drum cracks and thwaks that heavier hitting amps can provide. I can't deny that something CAN be said for high power. It's just that for the long haul, I keep going back to what seems to 'fit' best -- big, single-ended triodes that aren't nearly as strong in terms of output wattage as their comparatively impressive physiques might suggest. What they are able to do sounds right to me.

I don't think any amp I've used with K-horns has been " dead quiet." If one considers that term literally, the speakers would be completely and utterly silent -- inert with absolutely no sound whatever coming from either the bass bin, squawker, or tweeter. I have used lots of SET amps with directly-heated AC filaments, and some low level hum could be heard (and measured) with my ear right up to the sides of the enclosure. I've also used well-regulated and filtered DC on 2A3s and 300B cathode filaments, and even then am able to detect a tiny bit of residual hum/noise. Tweeters will exhibit very, very low background hiss with passive attenuation, but I've almost always been able to hear a slightly higher level of that sound (clean hiss) with active preamps. Never bothered me, it was confirmation the speakers and other components were alive and working, and from the listening position and music playing were, then, not a problem in the least. Some amps/preamps were quieter than others, though I have to say it wasn't always the most quiet designs that sounded the best. Erik

JBryan: "he 6SN7s have more of an impact on the amp's sound and I'd suggest rolling them first" That is excellent advice. The vintage globe 45s are really nice tubes -- handle them with care! Erik

I have also used a parallel feed output 2A3 amplfier with LaScalas, and thought the combination was exceptionally good. The Paramour should be a great match for the LS, as others have mentioned. We use a subwoofer with both our Lowther rear-loaded horns and Heresies. It can sometimes take a bit of experimentation in terms of placement, phase, and crossover point, but once it locks in place is very enjoyable. I honestly didn't realize how much I was missing until I listened to music with a subwoofer, given to me by my wife as a gift. I'm not in the least a bass fanatic, but do like to hear the lower frequency instruments reproduced at more realistic levels. Have fun, Erik

Jay: Just for the record: That capacitor upgrade I mentioned was in reference to the Transcendent OTLs, only. They just don't seem to change that much to me with more expensive parts. However, caps absolutely can alter the sound or voicing of an amp, and I have done that many times. Sometimes I preferred the more expensive part, other times not. Just depends on the circuit in question. Best 45? That's a tough one! Best anything is an impossible call for me! I'm not trying to evade your question, I just can't answer it. Cut-Throat has some excellent 45 amps, but I haven't heard the Star Chief. Parallel-feed outputs were really very nice, and MQ makes some very fine transformers for para-feeding. They also sell a grid choke that I loved -- JF Lessard's parafeed amp, the Horus was a truly outstanding circuit, and he used the little choke on the grid of the output stage instead of the usual resistor. Made a big difference to me, which is good, because that little hunk of iron is not cheap. Erik

Kevin: I've been doing, but for some reason when I post it looks like one large paragraph.

Clipped and Shorn " What is the deal with the plastic bags (transformers?)." I've done the same thing with plastic wrap. As described, it keeps them from getting damaged during the process of building. Jay: The Transcendent OTLs have been responsible for the most obvious difference we have heard among those we've used. It's honestly a bit surprising that we don't have one yet, though I have put together a dozen or so kits for others. I completely rebuilt a T-16 for someone and it seemed to have much greater power than its specs would suggest. Even the SE OTL, with an output in the range of the 45 triode we've been discussing, is capable of pretty amazing LF response. In the case of both the Transcendent OTLs, it wasn't only the extension of bass that's impressive. Those things seem to have a really uncanny sense of grip and control in the low end, while balancing that very well with extended mids and highs. While we don't yet have a Transcendent amp in our system, I can say without hesitation that they are among the very best we have heard. There have been some small ground loop issues that in the case of the T-16 is resolved very well with a small value resistor, and with the SE OTL an adjustment of the shield connections to ground on the inputs. However, having built several of those, I think I've stumbled on a cure that 'might' work well. Like passive crossovers in multi-driver loudspeaker systems, output transformers are a sort of necessary compromise: The parallel-feed we've talked about is an improvement on that, IMO, and there is no doubt that transformer coupling can sound incredibly good. OTLs just sound quite different, to me, in a positive way. I have also tried the so-called 'upgrade' with more expensive capacitors, and found very little, if any whatsoever, change in sound character. Common metel film resistors, electrolytic capacitors, and PP capacitors work just fine, though of course one should use what one prefers. I suspect that's one of the nice things about the fact that there are so many brands of passive parts to choose from! The SE OTL may not perform at its best with high order passive crossovers or where really high SPLs are needed/wanted. Wired for monoblock use, a pair of them on Klipschorns with play very loud. Erik -- trying to figure out how to make paragraph breaks here!

Jay: It's a reasonably common design using Sophia Electric 300Bs. This amp is really outstanding, and I love the sound of the 300B in general. I also own the Sophia Electric Baby amp, and for the money is a superb value, very well built, etc. I was shocked at what they did with our Klipschorns -- the match was better than virtually every other amp I've used with them. The Transcendent SE OTL and T-16 were also really, really fabulous. I have no doubt the Sophia Electric 300B MKII is outstanding. They're OPTs are worth the cost -- I know, that's what I got for these most recent amps. Erik

Jay: There is a ton of history behind this. The amp in question is actually rather different from the others mentioned, the most obvious of which is probably the fact the Tucker's circuit incorporates a parallel-feed (shunt) output stage. However, like Eliano's DRD, it also uses direct-coupling between the two stages, as well as a different plate-load approach for the input (as opposed to the ubiquitous plate resistor). In other words, both the DRD and JT45 lack the also-more-common interstage coupling capacitor between input and output. Many, including me, have found the direct coupling, either between plate and grid between each half of the input and driver stage, or between the input plate and output grid (note the absence of a grid leak resistor on both the JT45 and DRD) translates into apparently improved frequency response (we can also call that 'speed' or transient response), clarity, presence, immediacy -- or however one might subjectively choose to describe a stronger illusion of listening to live music. John Tucker's design, as far as the one I'm familiar with, also does not use vacuum-tube rectification, which, despite the strong tie many hold for vacuum tube rectifiers, may also contribute to the tightly controlled B+, which may in turn contribute to evidently very good frequency response at both poles. The JT also has a rather large bypass capacitor across the bias resistor on the 45 cathode. Larger caps in that locations can effect the low frequency cut-off point of the bandwidth of the circuit, and may contribute to this amp's apparent strong and controlled bass response in light of its comparatively small output power. I built a 45 amp with two vintage globe 45s a family member sent me, and I agree it can sound exceptional, though to my ears its strength is in the midrange and upper frequencies -- that's a good thing since the vast majority of music I listen to lives in that particular area. Also: Jack Eliano largely designed the Welborne DRDs. Eliano's first DRD design was a published schematic using the 300B triode, solid state rectifiers (which can sound superb, by the way). There are those who have incorporated elements of both the DRD output stage (bypass capacitor common lift to B+) and parallel-feed coupling to the speaker -- both I and another forum member have done that with good results (IMO). However, the actual current path of that arrangement has been perplexing at times. What it boiled down to for me was a sound that had superb clarity and 'presence' without glare and etch that's painful to listen to for long periods. Parallel-feed outputs have been around for such a long, long while. People like Dan Schmalle, John Tucker, Gordan Rankin, John Camille, and others have helped revive these antique-but-still-very-valid circuits for others. The Bottlehead parafeed amps are loved by many, and having built both the 2A3 and 45 DRD amps from Welborne Labs, I can say they are all quite good. One's 'cup-of-tea' sort of thing -- like everything in audio. I just recently finished a pair of 300B monoblocks using the Sophia Electric 300B and very old but wonderful sounding Philco 6SN7s. Superb sound with our Heresies and Lowthers, alike. I appreciate and really enjoy the picture of the DIY breadboard, which may have battery bias or filaments, perhaps? Very cool. Have fun, Erik

"For those that cannot verbalize the differences between their equipment choices, then my response might be: maybe those folks don't really care what they are listening to - but rather how much it costs, what name is on it, and whether or not it glows in the dark. Memetics is truly an interesting subject." Just thought I would submit another possibility: That what may have some bearing on this is not whether somone is or is not able to articulate differences among components or circuit topology, but rather, as was suggested above (with which I agree) that one listener's perception, interpretation, and subsequent description of the sonic signatures and characteristics of equipment choices may be drastically different from those of someone else. The only way to truly know whether an amp, preamp,CDP (or resistor or capacitor, for that matter) is right for you and your related equipment, regardless of what anyone has said about it, is to listen for yourself (if you can have that opportunity -- often we can't) with your own music, in your own listening space. Terms like 'warm,' 'clear,' 'transparent,' 'detailed,' etc. can't be relied upon in a universal sense, because different people have different perceptions of what those words mean. I've heard speakers described as 'wonderfully warm and rich,' (intended as positive attributes') where the same speakers were judged by another listener to not be 'warm and rich,' but 'drastically rolled-off at the frequency extremes, with tentative and bloated bass response, and virtually non-existent high frequency information." The class of amplifier might be one thing to consider, and yet there may be other important factors -- such as how the component interacts with the rest of the system (and room and the listener's own ears and brain) regardless of class of service. This said, I agree that some people may place more emphasis on cost, brand, and reputation, etc., -- and that is without question every bit their individual right. It's not for me to say what is or isn't right for someone else to do or value, and audio is only one rather less significant (in my opinion) example of that. My point is that it can be misleading to make choices based entirely on what has been said by others, but I have in fact done that many times. In some cases I was satisfied with the decision, others times not. This is not to say other people were being intentionally misleading. It's simply a matter of, as was also said obove, very highly subjective opinion. Have fun! Erik

Hi, Tom -- thanks I hope things are well with you and your family. Yeah, it was kind of a shock to see our old Lab Sarah when I logged on again. It was especially hard for my wife. Thanks for the thought on that. I've just been involved with lots of my own projects, and with school winding down and less papers and tests to grade, it's can be a nice way to relax. Erik

Hi, Phillip: Will also has most of the pictures. I posted the few I have, just because I knew you were interested. I do have a couple more I'll send via email, though. Erik

Very cute little pooch! It sounds like you've got everything you need for that project, Dave. BTW: In addition to TAS and Stereophile, I also get a couple of audio review magazines from the UK, and the last issue had an interesting piece on the psychological correlates of expense -- the implication being that it can sometimes be possible to fool ourselves into thinking and believing that a component (speaker cable and interconnect in this case) sounded better based on virtue of expense and visual appeal being the main determining factors. In the end, though, what matters is that he or she is happy with the result, and if higher cost had something to do with it, so be it! I've got several pair of 2A3s that are extremely expensive -- more so than the Sovtek version of the tube, costing many times less and sound outstanding. To me, the cost of the KR and AVVT meshplates was worth it, but they also look really cool, too. I also have a treasured pair of vintage RCAs that I just don't want to use out of fear of wearing them out. What a silly reason not to use a wonderful sounding tube, right? For another nice and even lower priced stereo tube amp kit, have a look at: www.tubesandmore.com This amp actually got some pretty decent reviews, and for under $200, just as your Decware amp, is a great way to get into audio DIYing. I totally understand your concern for Isabelle, and I think that's smart to take precautions. She really is a very neat looking girl. The lab in my Avatar had to be put down last December, which was really tough. It was a shock to post again on this forum and see her face looking back. Ok.....enough of that. Have fun with your new amp! I'm curious about how headphones might work. The connections are really easy, as I'm sure you know. Erik

Dave: See those blue rectangular thingies? Those are of course the interstage coupling capacitors. Two at .22uf. They were cheap, and they sounded good, but I took them out for the Jensen oil caps which cost more than the tubes, and I couldn't listen to the amp for long. It was easier to deal with connected to loudspeakers, but with headphones I couldn't stand it. I happened to have some common orange drop types in the same value, and they were better, but the best overall result was without a doubt the .22uf 630V Solens (that were less expensive than the first blue ones!) These are the same type sold with the Transcendent OTL amp I accidentally posted above -- which, by the way, if you want a good PCB soldering work out, is a good candidate. 22 tubes with nine pins to solder each, and that's just for the installation of the tube sockets! By the way, I have two nearly new Kimber caps in a .22uf value you can have if you would like to try. What do you need, two or four? They are well-made caps for the money; I just didn't care for the way they sounded in this design. Erik

That's the exterior of the amp with the Senheisers, before I decided to try the lower impedance and far less expensive Bose. I'm glad this came up, because it's a very good example of the importance of component matching, and how more expensive is not necessarily always better -- for a given design. The Bose phones with this amp are MUCH better than the HD 650s. Really significantly better, but the overall presentation is not nearly as smooth and 3-dimensionally layered as the Senheisers with the Moth amp. Anyway, here's the completely redone point-to-point wiring. Not much space to work with in this little thing. Erik

Okay. I had posted the wrong amp (a Transcendent T-16 I recently completely overhauled and rewired for a friend) and I had to figure out how to remove the image. So let's try again for the stereo 6BQ5, very similar, I'm sure to what Mike said above, and may have some elements in common with your own amp. If it were mine, I'd leave the wood! I want to show you a picture of a completely home-built regenerative radio receiver, particularly the wiring and lead dressing, that I commissioned from the father of another forum member. If one can use the word 'exquisite for electronics wiring, and I AM using that word, this is it.

Hi, Dave: Yeah, I suddenly realized I wasn't on the computer with pictures, but I'll post an outside and inside view, here. I had used this single-ended 6BQ5 amp as our main amp for quite awhile, but was never happy with how the factory-recommended parts placement and point-to-point wiring. So, I rebuilt while at the same time making provision for headphone use. The amp you just built might actually be an outstanding headphone amp, by the way, and you can either install a stereo phone jack or make an adaptor to take the headphone outputs off the binding posts. You would just need a femaile 1/4" phone jack to plug in the headphones -- or mini, whatever size would work. It's how I now use the Moth 2A3 amp I built. It is an incredibly good sounding headphone amp -- if one happens to be interested in headphone listening, that is. Stevet Deckert is a nice guy. My wife actually talked with him years ago about some project she thought I would be interested in, and he has always been helpful, as well as fair in his pricing for the first little kit amp he offered. Lots of people liked that, and he stuck to it at a time when there was some pretty 'enthusiastic' competition. I still think the original industrial gray version of that amp is one of the neatest kits around. On the coupling cap issue: What is the value of that -- .1uf - .22uf -- something like that? V-caps have gotten good reviews from everything I've read, and since you know how to solder you have the advantage of being able to experiment. The amp shown below has had a variety of higher-end capacitors in it, the latest of which were quite expensive Jensens I had. I've also used Kimber and others, and all of those, at least with headphones, honestly sounded too bright. Coupling capacitors DO make a difference, and it's always been my contention that one should use what works best for a certain design without respect to cost. I like the Dyna 70 I have with Hovland Musicaps, because the seemingly slightly better HF response sounds right in that amp. The one issue with this is that your amp is built on a PCB, and they can only take so much soldering and desoldering before the solder pads can get damaged and lift off. Then, it's surgery time to get things to work. Here's my wonderful little ASUSA 6BQ5 amplifier that sounds superb with my wife's.....ahem......Bose headphones. I also use a pair of Senheiser HD 650s, but their higher impedance is much better suited to the 16ohm output Moth si 2A3 I made (the amp was no longer in production -- I bought the parts and schematic).