Pure Class A SS vs Tube Amp

... my new preamp Michi P5 is class A design

@glennewdick makes an excellent point about usable volume control range. And that is a particularly important consideration in this case because the Rotel Michi P5 preamp has high gain. According to my calculations its gain is at least 16 db, and it may be considerably more than that depending on the combination of RCA and/or XLR inputs and outputs that are used. But even 16 db is well above average for the gain of a line stage.

Power amp gains generally tend to be in the area of 25 to 30 db. Your A21+, for example, has a specified gain of 29 db. But given the high gain of the preamp and the high efficiency of the speaker I think it would be prudent to avoid power amps having gains of more than about 20 db. (The gain of the XA25, btw, is 20 db; many of the First Watt amps have gains that are significantly less than that, which would be fine in this case).

Power amp gains are often not specified, but they can be calculated to a good approximation from the sensitivity spec that is usually provided, in combination with the specified maximum power ratings. Online calculators may be available for that purpose, or you can post back if you’d like to me to described how to do that calculation manually.

Finally, btw, virtually all preamps (and other line-level or phono-level analog components) operate in class A, even though some manufacturers trumpet that as a selling point.

Good luck. Regards,
-- Al

The hiss levels produced by some amps which may be perfectly fine with say 90 db speakers could very well be bothersome with 102 db speakers.

@almarg That's usually more of a preamp thing. Most amps are plenty quiet to be fine on a speaker of 102dB.


@lordrootman  One thing to be aware of is that the distortion of an amplifier makes a much bigger difference when dealing with a high efficiency loudspeaker! Solid state amplifiers are well-known for brightness and harshness; this is caused by the higher ordered harmonics they make of which I mentioned earlier. One thing I did not mention is how keenly sensitive the ear is to these harmonics- this is because it uses them to sense sound pressure over a 130dB range. So keenly sensitive is an understatement. That is why the 'very low' distortion of many solid state amps is nevertheless audible.


Most push-pull amplifiers, whether tube or solid state, have a character where there is a certain minimum power below which distortion actually increases. There are only a few push-pull amps where this is not the case (ours are some of those few). This is the origin of that 'first watt' thing, where there first watt has to be a good sounding watt. On your speakers this is going to be critical. On that account 99% of all solid state amps should be ruled out; if you really want to go solid state your options are few. The Nelson Pass First Watt amps are your best option in that regard.


But if you go with tubes you have a few more options! You don't need a lot of power (25-30 watts at the most in most rooms, provided its musical power). A lower powered tube amp with high resolution will bring you more satisfaction. I think it a very good idea that you do a shoot-out, since you probably want to get the most out of your speakers! Do an audition of some of the top contenders (tube and solid state) and I think you will see what I mean.


One further note- the amplifier will not need a lot of gain- 20dB will be plenty. We have quite a few horn customers; normally our amps have about 25dB of gain but with a simple adapter plug we offer, the gain of our amps can be reduced to about 15dB which knocks out a lot of the noise floor that you will encounter with many preamps. For this reason, many low powered SET amps have only about 15dB since they are intended to operate on high efficiency loudspeakers.

The bottom line here is take your time. What is important is that when you play the system, it convinces you of music and you want to spend time with it- that is what the investment is for. Matching the amplifier to horns is always critical, but if done properly the payoff is huge. I recommend bringing in your significant other (as long as the two of you enjoy similar music) as this whole thing works better if both of you enjoy the presentation. Above all- have fun!

I have had a pass labs INT30A. with Kllipsch Heresy and Crites Cornscala. .Sound good to me. INT60 even better. . Now have Pass Labs Monoblocks with same speakers   Really nice.Got over tubes a long time ago. Others will differ.

$6K amp for Klipsch KLF-30 may be a bit of over kill.
I've had Klipsh KLF-20 (and KLF-C7, KSP6) for over 20 years. Mine is not modified.
I've tried a few different amps (NAD, Rotel, Nakamichi, Plinius), and AV receivers (Yamaha RXV-3000, retail $2000 and Denon AVR 3803CI, retail $1600) for KLF-20, and to my ears, not much difference. My KLF-20 sounds just good.
However, I've had a few different speakers (Tyler Taylo, Tyler Linbrook, Apogee Diva, Harbeth C7-ES) and they all sound better than KLF-20 on stereo music (especially on classical and jazz). Though for Rock and heavy metal, KLF-20 sounds more live, but I don't listen to them often.
So, I use KLF-20 in my home theater setup with Denon, and other speakers in 2 channel stereo.
My 2 cents.