SET 45 Amp Driving Dynamic Speakers

Excellent, informative posts from my fuse-loving friends above.  ;-)  I have two Dennis Had amps, an SET and and SEP amp, one based on EL84 and the other on nearly any power tube you can get into the sockets, from EL34 to KT150's.  16 wpc and 6 wpc, respectively.  The smaller amp is sublime mated with the Spatial Audio Holograms and the bigger one drives my Zensor 3 speakers in the bedroom, both with all the power I need.  They both have a warm euphonic sound.  Rolling tubes is joy with these amps and some of the new tubes are as good as the pricey NOS tubes I have heard, particularly the Gold Lions.   

A type 45 can make about a 1 watt or slightly less running single ended.

To really appreciate what they can do (which is to say, they usually sound better than a 2A3 or 300b amplifier) you actually do need some efficiency and the only way to get the efficiency you need is with a horn system unless you are in a really small room, perhaps a closet.

If you drive the amp too hard, the odd-ordered harmonics that the ear uses to gauge sound pressure will appear. This causes the amplifier to sound 'dynamic'. In the initial opening post, we can see that this is happening. Its important to understand that this 'dynamic' quality is really the result of distortion appearing on the transients where most of the power requirements exist. Its a physiological interaction with how we perceive sound.

The problem is, once you know this, you can perceive it as distortion, not just 'dynamics' (in about 90% of audiophile conversations, the word 'dynamics' can be safely substituted with the word 'distortion' without changing the meaning of the conversation). So if you have read this far, I may have wrecked it for you.

You can prove this easily enough by obtaining a sound pressure level meter. They are available as apps for smartphones. You will see that its really not playing that loud- it just sounds like it due to distortion.

Atmasphere raises a valid point however context is essential. How loud is loud enough ? Clearly there’s no single right answer as limits are individually set by a listener. We all determine our respective comfort zones of SPL(sound pressure level). Tommie’s Audio Note speakers are 95-97 db sensitivity. If he listens at say an average SPL 75-80 db he’s using mini watt power i.e. small fractions of 1 watt. Depending on room size and music genre he is likely as happily content as he describes. The vast majority of his enjoyable listening could be occurring in the mini watt power region. numerous variables must be considered. "Just right" volume level for one person may be too soft or too loud for another.


Tommie what SPL do you typically listen at in your home? Not everyone seeks 100-110 db peaks.it all depends on what makes you satisfied.

I have owned many 45 SET amps as well as loads of other SET to get the best out of 45 I have had to biamp even on horns the 45 SET doesn't drive woofers well but is amazing  on horns. I have had some luck using with fullrange BLH with 45 SET. But I do see many SETing themselves up for failure by not matching loudspeaker to amp. 

When I checked my levels in the past, I didn't get much above 90 db on peaks. That was setting it as loud as I would ever want to listen. Most of the time, it was lower than that. 100 db peaks must be painful, not to mention the potential for hearing damage.

I'll have to pull out my db meter and check again.

I use an autoformer passive preamp. My understanding is that, in contrast to a resistive volume control, the output impedance gets lower as you lower the setting. This results in better sound at lower volumes, which corresponds with my experience.