Best Tube Amp for High Sensitivity Speakers: 45, PX25, or 300B?


I am looking to change / upgrade my tube amp.  I have a good, all-purpose Primaluna EVO 400.  It employs the EL34's and has a nice sound, especially in the ultralinear mode. Other components:  streaming from Innuos Zenith MKIII to Lampizator Atlantic DAC.  Everything playing through Daedalus floorstanding speakers with a 96-97dB sensitivity. Currently, my office / listening room is on the small side: 12'L x 16'W x 8' H, but I'm building a new listening room on our farm where I will later upgrade some components to fit a larger room.  Now, here are the tube amp options I am looking at:

Audion Silver Night PX25  8 Watts.  Very popular among some, touting a slightly more balanced, dynamic sound over the 300B.

Swissonor 45 SE  or  Tektron TK One 2A3 / 45 i   The 45 is the low wattage (2.5W) but sweet tone alternative. Considered by many to be one of the most musical out there. Of course, its low power makes it more restrictive, only efficient with high-sensitivity speakers and in more small-to-moderately-sized rooms.  It might be great in my current office but would have to work harder in a larger one later.

300B Integrated Amp, Make / Model not yet determined.  8-10 watts.  Of course, the 300B is making a big comeback and has wonderful characteristics, especially in the midrange and especially with certain genres of music such as acoustic, vocals, jazz, etc.  I heard one opinion from someone with a history of work in sound production, "The 300B is great if you just want to listen to a female vocalist with a guitar." One take on it.

Adherents of the PX25 and 45 tend to regard the 300B as a nice-but-limited cousin. I honestly have no experience with any of these three tubes.  I moved from SS to tube with the PrimaLuna, a well-built amp that I have increasingly felt carries some limitations that other tubes--more focused specifically on higher sensitivity speakers--would open up the sound in the lower frequencies and some tone qualities all around.

Any opinions would be welcome.

 

gregjacob

Showing 2 responses by atmasphere

Aavik Class D integrated are revelatory as well. Those who gave them a listen had their prejudice about Class D completely shattered. 

Yes, a lot of class D amplifiers in the last 20 years were pretty effective at giving class D a bad name. These days there are class D amps that give any tube amp more than a run for its money. I've been playing a set for the last 2 years and don't miss the tubes at all- I have the same organic, liquid mids and highs and plenty of impact in the bass and its actually easier to hear what's going on in the rear of the sound stage. No tradeoffs!

@gregjacob Something you want to consider before moving ahead blindly with an SET purchase is the difference between sensitivity and efficiency. Sensitivity is a voltage measurement (2.83V @ 1 meter); efficiency is a power measurement (1 Watt @ 1 meter).

If the speaker is 8 Ohms these two are the same since 2.83V into an 8 Ohm load is 1 Watt. Your speakers are a lower impedance than that; hence they are not as efficient as you think they are. You did not mention which Daedalus. If a 6 Ohm model subtract 1.5dB from the sensitivity measurement to arrive at the efficiency. If 4 Ohms subtract 3 dB since 2.83 Volts into 4 Ohms is 2 Watts, not 1, a 3dB difference.

Now the sensitivity measurement came into vogue in the 1970s when solid state amps became really common. Most solid state amps can behave as a 'voltage source', which is to say they can double power as the speaker load is cut in half (although a cheap one may not be able to do this at full power if limited by its power supply). OTOH, tube amps don't do this at all- in particular SETs. For tube amps in general, the efficiency spec is more useful on this account. If a tube amp is able to act as a voltage source, it will employ feedback (SETs usually do not) and will cut power in half as impedance is doubled rather than doubling power as impedance is halved. This makes tube power really expensive.

A further complication is you are talking about an SET. SETs have about 20-25% of usable power. Above that power level, even though they are not clipping, the higher ordered harmonics start to show up in their distortion. The ear uses the higher ordered harmonics to sense sound pressure. The result is they start to sound 'dynamic' since the power used in music is mostly on transients and now you are getting loudness cues on the transients (that are artificially generated)! This is why so many people talk about the 'dynamic' nature of SETs. They are misusing the amplifier by having a speaker that lacks efficiency.

The bottom line here is that unless your room is very small using an SET on your speakers is a Bad Idea. Quite simply you'll need more power. One other thing- SETs have trouble making bandwidth due to output transformer limitations. Effectively this means that to get hifi bandwidth the amp probably should not make over 7-8 Watts. Add to that the problem of usable power and you can see that 2-3 Watt isn't going to make it in most rooms with speakers like yours!! A more powerful SET will lack bandwidth and the typical way of doing that is to compromise bass bandwidth in favor of the higher octaves (IOW its a design consideration the designer has to face).

This does not mean that you have to leave any musicality on the table when going with another kind of amplifier! There are push pull tube amps that have the same kind of 'magic' of SETs and now there are even class D amplifiers about which the same can be said.

FWIW I have speakers that are genuinely 98dB efficient and I find I need at least 40-50 Watts and my room is a bit on the small side. I don't use all that power of course, but it does mean that the amplifier is loafing and as a result distortion is very low- this results in greater transparency (distortion obscures detail just so you know- you do pay a price for higher distortion amps like SETs!). Of course we all want the relaxed liquid mids and highs that SETs are known for but seriously that's no problem for other kinds of amps as I said. And there are those occasions where the system really has to use some power- such as playing the Saint-Seans Organ Symphony at a proper level and doing it without strain.

So if you really don't want to go down a rabbit hole and flushing dollars down the loo at the same time, IMO/IME avoid SETs with your speakers, unless you are in a very small room.