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In Reply to: RE: KSS OTLs posted by akino on February 04, 2015 at 04:15:24
I don't see the connection between reliability and lack of same vs the number of auctions or sales on eBay. You probably won't see another pair for years, or until next week. Anyway, they were indeed unreliable. They used a Futterman type "totem pole" output stage that typically requires capacitor-coupling to the speaker, because of DC on the output, but in the case of the KSS they used a complex servo circuit to eliminate the need for coupling capacitors. It may have been the unreliability of that servo that gave the amplifier a bad reputation. Ralph can probably tell you more. Products like the KSS are what gave OTLs a bad name.
Follow Ups:
Thanks for the info Lew. I was curious about these. I have a pair of M60s that I'm quite smitten with, but at times wish they had just a bit more power. Other times I feel they are fine.
I'm driving a pair of esl63s with my Atmas and am constantly blown away by the depth of soundstage, but can't help but wonder if a bit more power might be in order. Otoh, perhaps I should pair the Atmas with a different speaker.
Cheers,
Andy
What are the symptoms that lead you to believe you have a dearth of power?
I am not sure about the impedance curve of the 63. I do know that the Quad 57s present a nice high impedance and could be mated with a low power amplifier quite easily. In the 63 there is a time delay network which may suck up some power. Maybe Ralph can comment.
Symptoms:
They play fine, but if I am feeling really cranky (as in cranking it up) the m60s begin to exhibit a gentle type of distortion. (Almost sounding "wooly" in nature)
Wondering if auto formers would help here without detracting from the signature sound?
Thanks
Andy
True, they will help to drive a low impedance speaker, but the best cure for that problem is not to buy a low impedance speaker. For the gain in current, you lose proportionately in voltage. (An autoformer, like a transformer, can only alter the V/I ratio.) I don't think (emphasis on "think") your issue with the 63s is primarily low impedance. Again, I yield to Ralph, since he seems to know what's up with 63s.
Yep
Thanks Lew
Back to my original thinking and curiosity with higher power OTLs.
I'll keep my eyes open for a pair.
Cheers
Andy
Maybe Ralph can comment.
I can. ESL 63s need more power than 57s. M-60s can drive them fine, but a set of MA-1s does better.
I've had a dead KSS 100 sitting on a shelf for years now. I think the main problem with the KSS amplifier is that the circuit boards are potted. If a part goes bad there's no replacing it. In my example one channel has bad coupling capacitor and the other channel has a bad diode. Both are 10 cent parts that can't be replaced. Another problem is the output tube heaters are all in series tied directly to the AC line, a bit on the dangerous side. The 6DJ8 tubes are all in series also powered by a regulated source. You can't run one channel at a time for troubleshooting purposes, yank one tube and the whole amp goes down. I did reverse engineered the circuit and have a schematic somewhere. I posted here some years ago if anybody cares to search for it.
Craig
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