ZEN Class A Amplifier Circuit IRFP140 IRFP9240

At the beginning of 1999 I wanted to upgrade my little Onkyo system and bought some great speakers made by Dijon master Mr. Each is equipped with an Altec broadband with excellent performance (100 dB, yes) and the result is simply amazing. My little Japanese amp worked well, but with an aggression that didn’t match my temperament (or his). I realized that I had put my finger back in gear and should also consider replacing the electronics. But what?
The tube amp was probably ideal, but at what cost?

So I did some research to try and find something good and affordable for the modest budget I’ve put myself on.

RARE PEARL: ZEN

All audiophiles know this, there is no substitute for Class A, but it is almost impossible to find commercially because it is non-commercial. Three quarters of the power is dissipated as heat and the rest is used to amplify the sound. Who would dare to sell an amp that heats the room rather than amplifies the music? You might say there are excellent lamps, but at a minimum of 15,000 F, this is a choice that deserves consideration. While we wait for better days, if we want to approach perfection without putting ourselves in a state of excessive debt, we must roll up our sleeves and bring out the soldering iron.

ZEN Amplifier Circuit

Once connected, the reflex is to search the internet with the keyword “Class A”. After the automotive sites, we immediately go to the site of Pass Laboratories (you know, ALEPH amplifiers, field reference).

All Nelson PASS articles mentioned on this page can be downloaded in PDF format from the website at:

http://www.passdiy.com/legacy.htm

Nelson Pass published an article in 94 describing the implementation of the ZEN, an extremely simple or extremely basic amp with a 10-watt class-A MOSFET. Reading the article and perusing the diagram leaves you speechless. A single MOSFET (IRFP 140) to amplify the signal and one second (IRFP 9240) as the current source (2 amps).

It is so simple that the sound does not risk any distortion, so much that it is reversed and you have to be in phase by connecting the red plug of the speakers to ground and the black plug to the output of the apartments. the rest of the sound system.

Well tell me, this is a change from the 3, 4 or even 7 folded and symmetrical patterns you can see almost everywhere, moreover… It suits me anyway, because I like solder, but not much.

To put it right away: ZEN will not work properly unless you have 8 ohm speakers and an output higher than 90 dB.

So I started looking for a handful of essential components that, of course, no local distributor had in stock. In short, after waiting 2 weeks, I can start prototyping and there is no difficulty. First time or almost working (a little hum on left channel, quickly mastered).

Conclusion? Personally, I’ve never heard anything this good. Everything is clear, consistent, powerful, present, in place at the same time… This amp is amazing, we can’t say otherwise. Those who criticize MOSFETs are wrong, it doesn’t have the least aggressiveness when operating in class A and with strong currents. Harmonic distortion (to an incomprehensible rate) is purely second harmonic, as they say with lamps that provide a warm sound.

Yes, but it’s not just the sound that’s hot, it’s the MOSFETs too, especially after running for over an hour…

In class A, it is the strong constant current used to establish the rest point, not the transmitted power for the signal that causes the heating. The dispersion is therefore continuous and much higher than the power delivered to the loudspeakers. Thus, ZEN can go up to 10 Watts for sound reinforcement, but dissipates not far from 70 Watts permanently.

Even when mounted on good heatsinks, MOSFETs can go over 60°C at 20°C ambient temperature, but what about in the middle of a heat wave? Bringing Onkyo? It’s hard for me after hearing what I’ve heard. You better understand why we rarely find Class A amps on the market.
In fact, since I’ve heard my speakers work great with a 4-watt (class A) amp, why not turn the power down?

Source: http://michel.burdin.online.fr ZEN Class A Amplifier pcb schematic alternative link: