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SET 45 and their (real) required speaker efficiency

Hello,

Gosh, wasn't sure if to post in the speaker or amp sections. But here it is. 

I've got a Finale/Triode Lab F-300B Monoblock amp paired with the Omega Super Alnico monitors stated at 94.5db efficiency. It does very well with this amp and I'm very happy with the pair overall. With classical being 90% of what I listen to, I guess I haven't really pushed the system to its limits, but it delivers plenty of what I like with acoustic instruments. Harmonics (texture and timbre), tone, minor dynamic shifts (musicianship), etc.

My question is for SET 45 tube owners and recommended speaker efficiency. Do the 2 watts from these amps have a 'real world' threshold where they simply can't deliver under a certain efficiency rating? So, for example, my speakers state 2 watts and up are enough. But I've had a few people tell me that 94.5db is not enough for this SET. However, on the Decware site, it does put a pair of Omega speakers on it's site as, what I imagine being a suitable speaker to pair with their 2 watt amps. The amp I'm thinking of getting will have Hashimoto transformers and a 20 watt output transformer. Not sure if that will give a bit more for the speaker to use or not. Also, are speakers w/o crossovers something to consider if I need to go look for another pair of speakers? Finally, what would your experience with the 45 SET amp suggest as far as the optimal efficiency rating for these tiny two watts?

Geesh, it's 5:40 am, no sleep yet, please ask a question if all the above sounds like someone hasn't had sleep yet.

Anyway thanks folks, really appreciate any suggestions to an optimal efficiency.

take care,
rob


vvcv
atmasphere's avatar
atmasphere
11,793 posts
 
A type 45 based amp is really only going to make about 0.75 watts or so unless you are using some kind of super-45 of which a few exist.

My 45-based amp uses original RCA output tubes. My speakers are 98 dB and 16 ohms; very easy to drive but simply not enough power and my listening room isn't that big. So this is a very room and speaker dependent issue!
hedwigstheme
134 posts
 
See what John Kalinowski can make for you. Below is a fair idea of what you'll need:

http://www.bd-design.nl/contents/en-us/d132_John_Kalinowski.html

Or maybe one of these:

http://classicaudioloudspeakers.com/cgi-bin/index.pl?fs=2&upper=25&content=26

Or assemble your own but choose the right drivers:

https://greatplainsaudio.com/enclosures/


jc100
2 posts
 

I would also take a look at the source(s) that you will use - see how many volts they output and take a look as well at the required voltage input for maximum output of your amp.

Most sources output around 2 to 2,5 volts but not all.

My vintage Sansui tuner (TU-717) only output 1 Volt. For example, Decware Zen amps need close to two volts for max output. This means that I would never reach the max output with that amp with that tuner (at 1 V) without a buffer (like my Burson audio Buffer AB-160 - which adds 6 dB). This is not a problem with Yamamoto DAC (YDA-01) with 3,1 Volts output. On my other DAC (Wyred4sound), I can play with the settings (between 1 and 2,6 Volts)

Just to say that if your source does not output enough voltage for your specific amp. - you will not get the max watts from it and if you are already at the lower limit … it may screw up all other calculations about speaker's sensitivity and all. But maybe you already looked at that.  

ddriveman
171 posts
 
Most 45 SET amps are about 1.5 watts output and 2 watts is really stretching it. Distortion of the amps gets very high near their max power. So really, with a 45 amp, you want to not exceed 1w and preferable at 0.5 watt or less.
94.5dB even with 8 ohm and impedance friendly speakers are not efficient enough for your 45 SET amp to do serious listening. Can it be satisfying? Of course. Likely in a small room and with small ensemble classical music, you're listening at between 85-88db. The question for amp/speaker matching is really about headroom.
Here is how you can look at it. for every 3dB of speaker output, you will need to double the amp power e.g. if your speaker is 94dB/1watt/1meter efficiency.  Then for 97db, you need 2watt. for 100db, you will need 4watt. For 103db, you will need 8 watt.
Since you amp is only 2 watt, them your Omega speakers can only hit 97.5dB max and that's almost at clipping level. so your effective listening range is between 85-97dB i.e. 12dB of headroom.
But imagine if you have a 100dB speaker. Then your 2watt amp can generate 103db i.e. a listening range from 85db to 103 db which is 18db headroom. This is 6dB more than your existing Omega speaker i.e. 4 times more power.
So really, what it boils down to is that 45 SET amps should ideally be matched with speakers with a minimum of 100dB (in the correct impedance as your amp out impedance). Just my 2 cents.
roberjerman
4,319 posts
 
I have three SE amps: a 45, a 2A3 and a 6BG6. 1.75, 3.5 and 6 watts respectively. And a pair of Heresy's. The 6BG6 has enough (barely) to work. The other two are only good for headphones. 
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