What tube amp for Harbeth 40.1

It sounds “harder” and dryer. Musical instruments sound very good. I think for classical, I likely prefer SS.  However, for vocal, it is not as sweet, and the sound is less holographic.

The classic solid state complaint.

Pass Labs makes sweeter sounding amps, but not in your price range I suspect, since you also need some power. I would look into rolling tubes with the Mac and possibly placing it on a platform or other anti-vibration devices to help it out. I would also look at speaker cables, which are ***critical*** when using tube amps on difficult loads- the shorter, the better!

I watch that video, it is interesting.  But I have a question.  Is it really the speaker drawing power?  I don’t think the speakers draw power, but it is the amp pushing power, right?  
I have a question. if we play the same music, volume knob at the same level, to a more sensitive speaker, will it display that it is pushing the same 750W power? 

The amp makes the power and the speaker draws the power it can based on its impedance and the voltage that the amp makes. So for a given voltage, if the speaker draws one watt and its impedance is 8 ohms, into 4 ohms it will draw two watts if the amp is making the same voltage. Its a mathematical relationship.

Regarding the more sensitive speaker question, if the impedance is the same the power will be the same. Now the thing about more sensitive speakers is if the impedance is 8 ohms or more, the amp will not have to work as hard to make the same sound pressure level and usually will make less distortion. If it makes less distortion, it will sound smoother and more detailed (since distortion can mask low level detail). Now solid state amps in general tend to make higher ordered harmonic distortion compared to tubes, and so tend to sound bright, even though that distortion is fairly low. The reason we perceive it as bright is because the ear uses higher ordered harmonics to sense sound pressure and is thus keenly sensitive to their presence. It is this simple fact that is why tube amps are still around.


The reason solid state amps tend to sound bright is that usually they don't have *enough* feedback (some get around this by having none at all). Its pretty hard to design a circuit that allows for really high amounts of feedback (+35dB). So most simply don't. The result is that the application of the feedback itself, while suppressing some distortions, actually adds some of its own (which is almost entirely higher ordered harmonics; that which is not is IMD and both are very audible). Unless you can get over that 35-40dB range, this will be a problem, and its been a problem in solid state design since the inception of the transistor.


To get around this problem, many solid state amp manufacturers have resorted to a simple technique called 'lying'. But our ears don't lie- we've been hearing brightness and harshness in solid state amps for the last 60 years; that is why tubes and tube amps are still around decades on from being declared 'obsolete'.

No tube amp is likely to have the same dramatic bass punch as a powerful SS amp will. That's not why people buy tube amps.

These days most solid state amps have output impedances so low that they overdamp the loudspeaker; no speaker made needs more than 20:1 damping factor and many work better with less. An overdamped speaker exhibits a coloration that many call 'tight bass'. Yes, there is some punch but you really don't get much in the way of definition. Tight bass is something you hear in stereos quite a bit but its really hard to find in real life. In a nutshell in their zeal to create the perfect voltage source, amplifier designers far outstripped speaker designs in this regard!

Tested on my Spatial Audio X5, the 8W one sounds more dynamic.

Naturally- SETs make distortion in such a way that the distortion sounds like 'dynamics' to our ears. But I get your point- we have a lot of Harbeth owners as customers and somehow they seem to work quite well together.

 But  ... it takes many tubes, it would add to the cost.  I am not sure how expensive are the tubes ...

@gte357s the power tubes are about 27.00 each. In a lot of cases a full set of them for our amps is less than one tube for some SETs!


You will need some power for this speaker. It appears to have a benign impedance curve but if the sensitivity number is real, a 60 watts will be a lot better than 20! A lot depends on how conservative Harbeth is about their numbers- As I recall they are pretty conservative so the speaker is probably easier to drive than the specs suggest.