Alpha Nirvana 39w 8ohm Class A Amp

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. :eek:

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!
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Hi Hugh,

Here it is , C3 makes sense for compensation if Q3 is VAS but how come Tiny 1845 driving those mighty Mosfets? Or am i thinking fundamentally wrong.

Regards Dibya.

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........

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.

Hi Hugh,

What changes shall i make to use it with my 4/6 ohms speaker?

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?