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Erik Mandaville

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  1. 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.
  2. 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
  3. 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
  4. 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
  5. 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
  6. Here's an example: http://www.6moons.com/audioreviews/musicfirst/passive.html
  7. 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.
  8. 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.
  9. 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.
  10. 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
  11. 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
  12. 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
  13. 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
  14. Kevin: I've been doing, but for some reason when I post it looks like one large paragraph.
  15. 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!
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