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PostPosted: Tue Jan 30, 2018 11:18 am 
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I'm still throwing the idea around to get back into a power tube amp. The 300B and 845 SET designs, described by many to have the luscious midrange in the former, and tighter bass but still beautiful midrange in the latter are very appealing.

My speakers are 90 db and 4 ohms. The power amp is a Pass Labs XA30.5. While I don't listen loud, every once in awhile I can see the bias needle move out of Class A which means that the speakers are pulling at least 60 watts.

Many designs of SET are lower watts (<10). The highest I've seen is a parallel 845 SE monoblock design in the 50 watt range. This is a concern but it may be misplaced.

That said, I've read plenty of posts of users say that, to paraphrase, "don't let the low watts fool you. This amp handled better than my 250w SS." So is it that the transformers need to be really high quality and the watts don't matter as much? Are these two tubes in a single-ended design just not going to work well with my speakers?

I'm a little lost in what I should be looking for exactly in a power amp tube design.


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PostPosted: Tue Jan 30, 2018 11:53 am 
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Location: Milton, ON, CA
msommers,

My speakers are 90 db and 8 ohms. I use a 225 watt mosfet amplifier when I want to listen loud but I also use a Line Magnetic 518ia [845 tubes] rated output is 22 watts and works very well in my small room at moderate listening levels.

Don't shy away from tube amplification.

Audiois1st

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PostPosted: Tue Jan 30, 2018 12:14 pm 
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When you venture into single-ended triode tube amplification, proper speaker matching is paramount. Don't rely on nominal speaker impedance figures, you will need to look at impedance vs frequency plots, phase angles etc. The biggest mistake people make when venturing into the SET arena, is "trying" to make certain speakers work.


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PostPosted: Tue Jan 30, 2018 12:51 pm 
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Thank you gents, I appreciate the feedback.

Brf,

Regarding the plots you mentioned, can you help me with respect to what I should be looking for if I can acquire these plots and how that might help me match the amp and speaker?


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PostPosted: Tue Jan 30, 2018 2:23 pm 
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if the speakers are honest in the spec numbers....you should use like 100W of tube power to properly drive them( looking at the 4 Ohm load)...


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PostPosted: Tue Jan 30, 2018 3:30 pm 
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tube play loud, you might be surprise what an 8 watts can do :D


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PostPosted: Tue Jan 30, 2018 3:33 pm 
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you may be surprised I am the guy who had SET and horn speakers before all the craze arrived....


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PostPosted: Tue Jan 30, 2018 4:12 pm 
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Reading this got my curiosity up so I grabbed my Sophia Electric Baby ( 10 watts push/pull ) from the hobby room and plugged it into my Element Fires ( 8 ohm 88Db ) in the bedroom system and gave it a go. Bedroom is about 15 by 18 and I sat down about 14 feet back. All I can say is that unless you like to listen stupid loud this system has all the volume you'll ever need. Measured at my position with the volume at about 11oclock I measured 75 Db average and 84 peak on my somewhat cheazy IPad Db app. Sounds damn fine too. :D So, I'd have to think you would be fine with a quality SET amp and wouldn't need a ton of watts to get the job done.
My two cents...


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PostPosted: Tue Jan 30, 2018 5:07 pm 
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There is the old adage that "tube watts are better than SS watts". I'm not really sure I agree, but I have had various tube amps over the years and for the most part have stuck with tubes. I've had everything from 30 wpc to 100 wpc push pull amps plus a 300b with a handful of watts. What I've come to appreciate is that it's not the amp or the speakers, it's the combination and how they match and work together that matters.

I remember hearing some 3 wpc 300b amps with some lowther horns and the combination was incredible.

In my audio system, I recently moved from a 100 wpc AR VT-100 to a 75 WPC Ref 75 SE. The Ref 75, although less power than my previous amp mates very well with my speakers (fairly efficient Mezzo Utopias).

90 db might be a little low for truly flea sized SETs, what speakers are these?

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PostPosted: Tue Jan 30, 2018 8:24 pm 
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They're Tyler Acoustics Linbrook speakers based off the SEAS Thor design seen here, which has a frequency plot:

http://www.seas.no/index.php?option=com ... Itemid=365

I kind of anticipated that a 5-8w amp would not do the job but was hoping something around 15-20w with beefy transformers should do the trick.

From a technical perspective I guess the issue lies in that I lack the knowledge to understand "on paper" matching between amp and speaker specs.


Last edited by msommers on Wed Jan 31, 2018 7:16 am, edited 1 time in total.

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PostPosted: Tue Jan 30, 2018 9:53 pm 
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Location: Hamilton, ON, CA
I will eventually and just for the creativity of it build more powerful tube amps but I’m really happy with my 5 watts per side single ended EL84 amp feeding a pair of modified Yamaha NS-344. The same amp was a mismatch with a pair of NS-690, the pair which I then sold. Point of the story is that you have to try at least some combinations. But one basic rule will never change when it comes to low-power tube amps - the more efficient speakers, the better...

It’s a widespread craze - people cherishing a pair of lower efficiency speakers, then intrigued by the fame that low-power SE tube amps possess they get one and then they end up bitching and complaining and proclaiming SE tube amps fuss misguided. No wonder. How about this instead – let a SE amp be a base on top of which the right speakers are to be added. The process demands certain dedication, yes, and the rewards are usually awesomely proportional to the amount of the same.


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PostPosted: Wed Jan 31, 2018 5:30 am 
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msommers wrote:
Thank you gents, I appreciate the feedback.

Brf,

Regarding the plots you mentioned, can you help me with respect to what I should be looking for if I can acquire these plots and how that might help me match the amp and speaker?


Please see the link below:
http://www.audioholics.com/loudspeaker-design/understanding-impedance-electrical-phase/page-2


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PostPosted: Wed Jan 31, 2018 6:53 am 
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If you can, specs will help you narrow it down, but ultimately you need to try t listen to an amp with your speakers to see if you like the combination. Can you always do that, probably not, but it's worth trying if you can. This is where working with a reputable dealer may help, some perhaps many will let you do an in home trial and I'd encourage you to do so.

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PostPosted: Wed Jan 31, 2018 2:00 pm 
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msommers wrote:
I'm still throwing the idea around to get back into a power tube amp. The 300B and 845 SET designs, described by many to have the luscious midrange in the former, and tighter bass but still beautiful midrange in the latter are very appealing.

My speakers are 90 db and 4 ohms. The power amp is a Pass Labs XA30.5. While I don't listen loud, every once in awhile I can see the bias needle move out of Class A which means that the speakers are pulling at least 60 watts.

Many designs of SET are lower watts (<10). The highest I've seen is a parallel 845 SE monoblock design in the 50 watt range. This is a concern but it may be misplaced.

That said, I've read plenty of posts of users say that, to paraphrase, "don't let the low watts fool you. This amp handled better than my 250w SS." So is it that the transformers need to be really high quality and the watts don't matter as much? Are these two tubes in a single-ended design just not going to work well with my speakers?

I'm a little lost in what I should be looking for exactly in a power amp tube design.

Hey Matthew!
While not 300B or 845 driven, you are welcome to borrow my humble 6.5W (sounds much more powerful than 6W!) SET integrated for sh!ts and giggles.
It's mostly sitting idle since I moved to active bi-amping my Linns with silicon.
It definitely does not have the pedigree of your existing pre/power units, but may give you a taste of the SET midrange magic, and inform as to power drive capability with your current speakers.
I found the following Decware info page interesting for their take on power requirements vis-à-vis speaker sensitivity: http://www.decware.com/newsite/buyingguide.html

Cheers!
David


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PostPosted: Thu Feb 01, 2018 7:45 am 
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Thanks for the offer, David! I think I will take you up on the offer once I have more hours on the speakers. I'll make sure there's beers in the fridge :)


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