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In Reply to: Re: Atma-Sphere class A OTLs posted by Ralph on December 28, 2006 at 10:22:30:
"If you are the same Kurt that I am guessing you are, you ought to take a listen to what we've been up to in the last 8-9 years. The kit that you built really only hints at what the amps do now days."Yes, I am probably that same Kurt you knew way back then. I contributed to ASOG and all that when I built the M60 in kit form and modified it ad infinitum and was a rather prolific writer back then. Yes, those are great amps then as I am sure they are better now, especially now that there are teflon caps to replace those polystyrenes. I wish I could afford your products today. But times have changed and I cannot afford any of your products at this time, and I was only able to afford what you had because it was in kit form back then.
And anyway, I am really quite satisfied with what I already have now. I really do believe in the SET sound for me. Even with the OPT's. But, of course, realize that I have direct-coupled passive-equalized amps with cobalt OPTs in a 45 SET package with ultrasonic AC DHT heating. And that just about trumps everything I have heard to date, P-P, SE, OTL, anything. You're not going to make me believe there's much better out there, at any price. Even if it were true, it seems inconsequential to me to try pursuing at this point.
Yes, I think I have hit the end point of this game. If I had a spare $5K to spend, I would improve the drivers of my B-D Design Oris 150's to their top of the line units. Unfortunately, we have a near zero output manufacturing country that causes the Euro to inflate to 1.33 USD from 0.87 USD in less than 5 years. So I no longer look forward to that upgrade.
Kurt
Follow Ups:
45s don't make a lot of power- I have to imagine that the Oris horns are essential. I've heard very good things about them- we have a few customers running them.I for one am not done with the American economy or production capabilities yet; obviously I think we still have a lot to offer.
It sounds like you have built up a pretty serious custom amp- not too many people use HF to run heaters. Had you thought about building more of them for fun and profit?
"It sounds like you have built up a pretty serious custom amp- not too many people use HF to run heaters. Had you thought about building more of them for fun and profit?"Yes, but then I think about how hard that would be and how much money it would drain me for a very small niche market. I really don't know why manufacturers haven't caught on to the ultrasonic heating for DHT's in SETs because A) it sounds better with a blacker background, and B) nobody wants any hum on even 110 dB sensitive speakers like I have. Also, it only costs about $100 additionally in parts to have this feature. Not bad for high-end SET amps of $5K or more out there. It's just lucky that 45's don't hum all that badly in the first place, but why have any hum?
(You know what's the coolest thing about ultrasonic heating? You use small ferrite toroid cores with 20 or so windings per side and you have an isolation transformer capable of delivering enough power to fully heat a 300B and have it floating properly. Nothing to it! The magic comes from the high frequency for making cheap tiny transformers to do the job. One power supply, one oscillator, one small class AB power amp (a power op amp might do) and two or more small isolation transformers.)
But also, one of the best attributes of my amp is that it has 01A DHT drivers which sound so exceptional there, and there's just no way of putting that tube into production because those delicate thoriated globe DHT's are only found used today. And it's not a good choice for a broad application anyway because the input sensitivity of my amp is now too low for most people. Thankfully, I designed my own phono stage with so much gain it more than makes up for that. But this is an all analog system.
For digital I go to my HT system. That's good enough for digital to me.
Kurt
Its base is a great-sounding 2-channel system that uses ASL SETs and DIY high-sensitivity speakers...
I've added full-range, diffuse-source surround speakers and am still using the Eminent Tech. 12 centerchannel speaker. Preamp is the fabulous-sounding 6-channel, tubed, c-j MET1. Sources are all digital, and they sound plenty good to me.
It's VERY satisfying--BIG, spacious, warm, well-extended and -defined in the bass, and surprisingly so for such inexpensive main drivers, highly transparent--for all the music to which I listen, which is mostly large-scale Classical stuff but also including small-group jazz and even smaller-scaled stuff.
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Tin-eared audiofool and obsessed landscape fotografer.
http://community.webshots.com/user/jeffreybehr
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