but you can start building 
Hello again.
I apologize for not speaking English, but I use online translator and may have inaccuracies in the expression.
A few pages back I showed you my Apex A40 and for several years listening was the best amplifier of all I compared it. Apex plays much better than factory amplifiers for a lot of money.
That's why I started a new project.
I start building 2 mono block with A40 circuit in bridging mode with 2 wires per bridging channel.
I think I'll lift the rest of my life and I'm convinced it will improve the sound.
In the process of building I will show here step by step.
Here's the beginning.
I apologize for not speaking English, but I use online translator and may have inaccuracies in the expression.
A few pages back I showed you my Apex A40 and for several years listening was the best amplifier of all I compared it. Apex plays much better than factory amplifiers for a lot of money.
That's why I started a new project.
I start building 2 mono block with A40 circuit in bridging mode with 2 wires per bridging channel.
I think I'll lift the rest of my life and I'm convinced it will improve the sound.
In the process of building I will show here step by step.
Here's the beginning.
You do not need to put A40 in class A, output stage of A40 work as class A.
I like your speakers - do you have a thread where they are emdescribed in more detail? Looks like an Omni reflector sphere made from a glass globe and a ribbon tweeter set back for time alignment. The woofer appears to be small voice coil cloth surround high sensitivity full range like a Phillips in a column MLTL with down firing port. What kind of XO is being used?
Sounds very nice! But where’s the A40?
Regarding Class A, these amps were optimized for Class AB, and I am not sure you will find much benefit of taking them to Class A except a lot of heat.
I have taken the FX8 into Class A before by dropping voltage and increasing bias to 1.25Amp. It did not sound or measure any better. If you are interested in Class A, perhaps start with a Class A design. They need not 40 actives to sound great or measure beautifully. Your speakers look quite sensitive so perhaps 52w of pure SE Class A is enough? Check out the Alpha BB amp.
Aksa Lender P-mos Hybrid Aleph (ALPHA) Amplifier
Bias current is 3A and rails are +/-36v all through a pair of TO-264 600w capable MOSFETs:
Aksa Lender P-mos Hybrid Aleph (ALPHA) Class A Amp GB
Hello xrk971
Most circuits in class A have a differential amplifier.
Here with colleagues and friends we have come to the conclusion that he inserts harmful artifacts at medium and high frequencies.
A40 has no differential, sounds clear and transparent, so we want to raise the milliamers and increase the transistors. So avoid A / B switching and have constant linearity at the big transistors.
About omnipolar speakers:
MHT 12 - 8 Ohm | Visaton
B 200 - 6 Ohm | Visaton
W 300 - 8 Ohm | Visaton
Most circuits in class A have a differential amplifier.
Here with colleagues and friends we have come to the conclusion that he inserts harmful artifacts at medium and high frequencies.
A40 has no differential, sounds clear and transparent, so we want to raise the milliamers and increase the transistors. So avoid A / B switching and have constant linearity at the big transistors.
About omnipolar speakers:
MHT 12 - 8 Ohm | Visaton
B 200 - 6 Ohm | Visaton
W 300 - 8 Ohm | Visaton
The Alpha BB uses the Aksa Lender front end which is not your usual balanced input that nullifies even order distortion and contains higher order odd distortion. If you look carefully you will see that the VAS is a single KSC1845 strapped across the two tails of the balanced Long Neck Pair (LNP), not LTP. The Aksa Lender has the advantage of low THD for transparency and dominant 2nd order HD with less 3rd order HD and not much else. Very similar to a SE Class A triode but without the high THD.
The basis of the Aksa Lender is in this Preamp:
AKSA's Lender Preamp with 40Vpp Output
Here is FFT of the Alpha 20 (smaller version) but same profile.
Here is FFT if the Alpha BB, 2.86vrms into 8ohms:
And all of this is done with minimal negative global feedback for flat phase for superb soundstage.
Thanks for sharing details of your drivers. I have not see that tweeter before. Is it like an AMT?
The basis of the Aksa Lender is in this Preamp:
AKSA's Lender Preamp with 40Vpp Output
Here is FFT of the Alpha 20 (smaller version) but same profile.
Here is FFT if the Alpha BB, 2.86vrms into 8ohms:
And all of this is done with minimal negative global feedback for flat phase for superb soundstage.
Thanks for sharing details of your drivers. I have not see that tweeter before. Is it like an AMT?
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You can use output stage from AA14 or AA9 and use it instead diamond output stage of A40 if you want. There is AA5 class A amp with single transistor input.
