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In Reply to: Lynn Olsen designs vs. others posted by KurtP on March 11, 2007 at 16:33:40:
I realize this post is going to cause a lot of folks to think poorly of me, however.Having built all of the magnetics in Lynn's Karna amp, I can attest to their complexity and level of performance. I doubt that anything short of the massive HV SE amps can compete with the Karna in detail, musical expression, micro and macro dynamics and size. The latest version is now using Gary Pimm's SS CCS and separate B+ transformers for 2A3 and 300 B B+ stages. Lynn has also switched his input splitter to Tribute's excellent toroid. If you email me I will provide you with the schematic of this latest version. If you are seriously considering making these amps you must contact Gary Pimm and discuss the unusual ground plane solutions required and I can provide you with his email address.
Lynn's Amity amps, as have been built by Gary Dahl and many others, are somewhat easier but without the 35 watts of clean audio power the Karna provides. more in line with the 20 watts suggested by other posts. They are extremely musical and are well suited to the same level of efficiency you are dealing with.
If you are ready for a challenge there are two other brave souls currently on planet who are either building or planning to build the Karna's, so there will be some folks to discuss solutions with, in addition to Lynn, as he heals his broken leg, Gary Pimm and myself.
Follow Ups:
Thank you, for the reply, Bud. You are clearly more than familiar with the construction.To be honest, it is the complexity (and cost) of the Karna that has caused me to shy away from it. Sure, I think I could build it, but the sheer cost of the tubes (45 = $$) alone makes me cringe at the thought of my wife seeing the bill. In addition, my direct experience with DHT's is too limited to tackle the size of Karna and its ac heating. So, yes, I have been leaning the Amity direction. It is my belief and hope that the ME2's will be more than happy with the Amity.
I am a little miffed as to the complexities of the grounding: to me, it all seems fairly straightforward - basic instrumentation grounding. I have read the boring and informative IEEE Emerald book, and would follow those rec's above all others.
If I head this direction, I will certainly contact you regarding more info. I am currently using the schematic shown on nutshell's site. Is that not the best version?
Kurt, good luck on your quest. I built and use Amitys in both 2a3 and 300b versions. The signal iron in both is Lundahl. On the 2a3 version I used Hammond power transformers and chokes. On the 300B, I used all Lundahl iron throughout. I used a modest OT on the 2a3, the amorphous core OT on the 300B. Both amps are very good. It seems to me that once you get to the level of performance of the 2a3 version (even with its more modest OT), the cost to upgrade performance rises dramatically, and you have to decide how much that extra fraction of a percent of accuracy is worth. If you haven't looked at the K&K audio forum, please do - there is a wealth of info on these amps at this site. Additionally, Kevin has a transformer couple KT88 design posted in the projects section that might interest you was well.
Most of the horror facing Gary Pimm, while constructing the Karna's, came from having two chassis, with power mostly on one and signal and the tubes on the other. There are so many tubes and transformers that even one gigantic box would not have held them all. The entire ground scheme was made from Nylon selvage covered Litz wire and if you copy nothing else in your instrumentation grounding scheme, copy that.Gianluca is absolutely correct about the interstage being the key to the amps performance. These amps are just so revealing that even the deservedly well thought of original interstage's, were found to be wanting. Took me several iterations before learning how to balance low permeability gain and this unusual sensitivity to the internal coil capacitance's.
The current units in Lynn's amps, being level three on our performance chart are ruler flat to 20k and then climb to +6 dB at 35 k. Too many turns within the same winding space. So, it will take a larger unit to flatten the highs while keeping the permeability increase to a minimum and so controlling the overall distortion, but specifically where the core becomes permeable, 1 kHz and lower. Level one interstage's do not have this problem with skewed performance, but they are not as revealing either.
I agree with most folks here that a triode connected PP with perhaps a SE driver stage to a voltage splitting transformer coupled interstage will be good enough to soothe the need for music and dynamics from what are some of the best speakers available.
My personal amps are input splitter transformer to PP parallel 7119,s to an 1.414 to 1 PP step down interstage to eight EL 34's in PP paralell to a 1560 z ohm output we originally supplied to Cary for their 6 pac amps. Very noble, powerful, amazingly detailed sound. The only passive components are the grid blockers.
So, don't just look at the DHT amps, as other tubes and topologies are actually equaling that delightful performance and providing power to boot.
I'd strongly recommend that the OP goes with Lynn Olsen's designs. I'd add that he should use DHTs all through, including the first stage and driver. DHTs are important and so are the interstages. Get those right and you have your amp for life.Bud is being a bit modest here - I have his 6.6k Push Pull OPTs as used in the Olsen designs and they are superb. I'd start there (not sure what the waiting list is like - you may have to get your order in!) and then consider the interstage options - have a look on the K and K site here for the Lundahl options with amorphous cores, or as said consider Tribute and one or two others. To keep costs down you can use Russian or Chinese 2a3 or 300b in the first instance to get it working.
But a word on chassis - isn't it possible to build this fairly easily on two 2u rackmount 19" chassis? My current all DHT transformer coupled balanced Push Pull amp is built on a single 2u rackmount chassis - wouldn't do it again, it's too tight. But a couple of chassis - surely that's OK?
And considering the problems with approving umbilicals in domestic equipment (in the EU virtually everything is not approved for higher voltages DC), two monos rather than a PSU and a signal chassis.
I was not clear enough in my description of Lynn's amps. They are split into four chassis, sort of a dual mono with respective channels power and output chassis connected with a very serious umbilical. Your estimate of size is just about spot on too and just barely big enough at that.
Four chassis ?I was also thinking about the monoblock design, attempting to keep the PS and amp proper together. Maybe what would make this more possible is additional R-C filtering, removing the CCS? I know many would frown on this, but Lynn seems to indicate both methods worked well.
I would definitely be interested in recommendations for all transformers, and will get advice from K&K. No doubt, though, they will push for all Lundahl throughout. If the tribute is best for input, and James for output, I would absorb all recommendations.
Thanks for your help. Can't seem to locate O-Netics website?
Check the Karna print from Lynn's website, contact information should be on it.
Triode, UL or pentode mode?
Triode only. The original OPT's for Cary(these) did not have the 43% UL tap, not that it would have made much if any difference. All production did have UL taps. I did not like the sound of this amp with UL or in Pentode mode with the needed feedback, so Triode it is.
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