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Parallel SET with sufficient power

Hello all:  I'm looking to move back into SET land after 15 years. I have a pair of KEF Reference 3's at 88 dB sensitivity which I'd like to keep, so I'm considering a parallel Single Ended design with at least 30 WPC. I do like the '300B sound' so friends have recommended the 6C33c tube in parallel to deliver 30-40 WPC. I've read some very positive posts on Audio Mirror and Wall Audio of Germany was briefly mentioned. Smaller boutique like companies give me some concern as most of these fine designers or engineers build amplifiers in their spare time, and quality control may be compromised.  I'm not a huge fan of 211 or 845 sound but these amps are another option.  Thanks for allowing me to think out loud and I do appreciate all opinions!

normie57
mani-2
42 posts
 
If you wanted to stay with SET, amps based on the 845 usually put out about 30 watts a side. And then there's the ever-classic Cary 805 at 50 watts each: https://www.audiogon.com/listings/tube-cary-audio-design-805c-single-ended-triode-monoblocks-50-watt...
jbrrp1
423 posts
 
I have a pair of Lampizator 211 mono's that run a pair of 211 per side in parallel, and I can confirm that Al and Ralph are tipping you off correctly.  My 211's boast 85 watts of a tube power, but when I tried them on a speaker that dipped down to 4 ohms in the lower mid - bass range, it resulted in an anemic balance.  It isn't so much about watts - - it's about proper impedance matching to achieve proper frequency response and tonal balance.
georgehifi's avatar
georgehifi
10,312 posts
 
 My 211's boast 85 watts of a tube power, but when I tried them on a speaker that dipped down to 4 ohms in the lower mid - bass range, it resulted in an anemic balance.
This could very well have been the output transformer, being 8ohm. If it had a 4ohm tap it could have been a different story, also Lampi may use no or very little negative feedback this will also have a bearing if it can drive a lower impedance as well. (having feedback lowers the output impedance) 
The amp I linked to from reading on the web has user adjustable negative feedback (which lowers the output impedance) as well as 4ohm taps.

Cheers George 
atmasphere's avatar
atmasphere
11,861 posts
 
@georgehifi , there’s more to it than that... generally speaking, SETs behave as power sources rather than voltage sources (which might be your typical solid state amp). The reason to go this route is to avoid the brightness and harshness often associated with loop negative feedback (harshness and brightness is after all a coloration and not one that is particularly pleasant).

Because no feedback is used, you can’t rely on the Voltage Paradigm for flat frequency response, and the 4 ohm tap may or may not help (likely won’t, as the speaker may be looking for +3db worth of power in the woofer section, and merely moving to the 4 ohm tap won’t get you that).

There are speakers that are designed to work with amps of higher output impedance (and no feedback): Merlins, Coincident, Audiokinesis, Quad 57 and Quad63, Classic Audio Loudspeakers, Rogers LS35A, Lowthers, PHY, Festerex, most horn speakers and many more.
georgehifi's avatar
georgehifi
10,312 posts
 
Sorry Ralph I was talking about driving the OP’s speakers with two low 3ohm impedances around 50hz and 150hz, my experiences and measurements on the same amp a 4 ohm tap output tap has a better chance of driving a speaker that dips to 3ohms in the bass as the OP’s do at 50hz and 150hz, than an 8ohm tap on that same amp.
Also if on that same amp the global feedback is increased, it will drive it even better again as it lowers the output impedance even more. But may not sound as "euphonic".
Sure there are spl limits with a 45w set/ or push pull just as there are with a 45w solid state

Cheers George
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