The higher powered amp (350 watt class D) had a little more dynamic range and bass slam but the Alpa Nirvana has a richer sound, and the system reveals more of the recording engineers skills, some recordings the room is filled with music others it is just in front of you.
Whilst I agree with you about the sonic qualities of the AN, @wirewiggler ... some spkrs will unfortunately need more grunt than a 40w AN can provide - that's where a high-powered amp is needed. 
I am fortunate in that the 2-way active spkrs I designed, sound very, very good with my 40w AN ... and I never see the red 'clipping LEDs' light up! (Mind you - they hand over to subs @ 110Hz - with 48dB slopes - which lessens the power draw on the AN).
Whereas a mate of mine who runs some B&W standmounts:
* started off with a 40w tube amp - which sounded very nice.
* then changed to a 150w ss amp - which made the B&Ws sound better!
* and now has a Sanders Magtech (500w into 8 ohms / 900w into 4 ohms) - which makes them really come alive!
I am fortunate in that the 2-way active spkrs I designed, sound very, very good with my 40w AN ... and I never see the red 'clipping LEDs' light up! (Mind you - they hand over to subs @ 110Hz - with 48dB slopes - which lessens the power draw on the AN).
Whereas a mate of mine who runs some B&W standmounts:
* started off with a 40w tube amp - which sounded very nice.
* then changed to a 150w ss amp - which made the B&Ws sound better!
* and now has a Sanders Magtech (500w into 8 ohms / 900w into 4 ohms) - which makes them really come alive!
GATE DRIVE AT CLASS A
You are right; it's a phase lead compensation cap.
In a Class A amplifier, the outputs do not switch, so their gate drive can be relieved considerably.
There are no reversals on the gate current to switch on and off, so a small VAS collector current is more than adequate.
I recall studying the charge cycle at very low VAS drive and being surprised how little current was needed up to 20KHz.
As Adason remarks, I did increase the drive with a larger transistor (3503C) in subsequent version.
If this were an AB amplifier, you would need at least three times the current to drive the output gate.
The gate requirements on these IRFs are low when always turned on........
Hugh
You are right; it's a phase lead compensation cap.
In a Class A amplifier, the outputs do not switch, so their gate drive can be relieved considerably.
There are no reversals on the gate current to switch on and off, so a small VAS collector current is more than adequate.
I recall studying the charge cycle at very low VAS drive and being surprised how little current was needed up to 20KHz.
As Adason remarks, I did increase the drive with a larger transistor (3503C) in subsequent version.
If this were an AB amplifier, you would need at least three times the current to drive the output gate.
The gate requirements on these IRFs are low when always turned on........
Hugh
Well, there is a 4R version in this thread as I recall, but essentially you will have to increase the quiescent to about 3A.
That will hugely increase the output device dissipation at the existing 27V rail, but with a lower impedance to achieve 39W you don't need more rail voltage anyway; 20V or even 22V would be fine. You are advised to move to FQA40N25 and FQA36P15 mosfets, which have a pd of 280W apiece.
Check the thread; I designed a version for 4R and AndyR has built one and I have heard it working very well.
Cheers,
Hugh
That will hugely increase the output device dissipation at the existing 27V rail, but with a lower impedance to achieve 39W you don't need more rail voltage anyway; 20V or even 22V would be fine. You are advised to move to FQA40N25 and FQA36P15 mosfets, which have a pd of 280W apiece.
Check the thread; I designed a version for 4R and AndyR has built one and I have heard it working very well.
Cheers,
Hugh
I can send you the 4R schematic - if you can't find it in the thread. I use 22v DC rails.
If your spkrs are 4/6 ohm ... you might like to seek input from people here as to which would be the best version for you to build.
* the 8R version is 39w into 8ohms ... and so presumably, more (50w?) into 6 ohms. However, someone in the thread posted that his 8R version didn't like driving a 4 ohm load!
* I have measured my 4R version and found that I got 40w (at clipping) into a 4 ohm load - but only 31w into a 6.2 ohm load. Is this enough for your spkrs?
@andyr Even 10 Watts are enough, my speaker are very efficient Phillips India 3 Way from 1980s with Silk Dome Tweeter and Mid range from Peerless India, infact my Grandpa use to use single ended Tube AMP with it who previously owned it, that amp produced max 7W.
I will love if you sens me the schematic
I will love if you sens me the schematic