MJL3281/1302 based amplifier ?

[guitar89]

Well.... being one of the powerful transistor, which I have excess.
I want to make a clean, nice amplifier that is Hi-Fi, at least capable of moderate power (20W).

Any recommendation ? Doesn't like too high power, but will accept too, preferable something near 20W. If there is class D project, I would like to do that (haven't tried one)
Would like to build at minimum cost though, but willing to build if it is highly recommended ! (my pocket are tight, but willingly to sacrifice for the name of AUDIO)

[ingenieus]

The MJL3281/1302 are very good transistors and capable of delivering far more than 20W. If you use enough of them, more than twenty times that is possible. Even a single pair is good for 50W or more.

Class D and 20W do not usually appear in the same sentence. The extra complexity is not worth it when you can use an IC such as the LM3886 to do the same thing. But if you want to do it to learn the ropes of class D amps, not a bad idea.

If you already have the transistors, the next step is the transformer. Have you got one already or are you going to buy one? This will determine what sort of amplifier you can build. For a 20W project, a 15V-0-15V 100VA transformer will do nicely.

[guitar89]

haha, i have a 120VA 25V-0V-25V transformer X.x Then usually how much is class D are rated ? Well.... I personally love the topology of Class D, and want to know HOW good is it, and i love the aspect of less heat ! (how complex is it ?)
I don't like Class D chip, most of them are SMD type with many legs and hard to solder (I hate soldering small things)

I personally doesn't love loudness much (maybe occasionally party booming is nice), but i prefer nice sound quality (Hi-Fi). And the reason i brought MJL3281/1302 not because its power rating, but its their response, SOA, Ft, etc (in general, good sound quality capable in spec)

Maybe I could make an amplifier with few pairs of output transistor, then reduce the gain when I'm not using for booming (more NFB, better quality ?)

[AndrewT]

25&25Vac will give ~ +-35Vdc as a PSU after rectification and smoothing.
A single pair of 3281/1302 will give a reliable 8ohm capable ClassAB amplifier that should last your lifetime. Expect about 50W maximum into 8r0.
Remember, the operator controls the volume level. Yes, you! You determine how loud the resulting sound.

[guitar89]

ah... i love the sound of amplifier you said. But where could i found amplifier such as this ?

[AndrewT]

Look through this Forum.
There are probably dozens of successful builds using that arrangement of device & voltage and impedance.

[ingenieus]

Try this thread as a starting point:
My new SymAsym PCB design Rev_1.3

The design presented there will work with the 3281/1302 without any changes (the designer said so himself in one of the posts). The supply rails are +50V but this can be changed as well. For optimal results the input stage should be tweaked for the lower voltages but it will still work if you leave it unchanged.

For questions on Class D, this is the wrong part of the forum. You can post such questions here:
Class D - diyAudio

[guitar89]

well..... although i say i favor class D, I also accept other "clean" amplifier design. Will look into the link.

[Nico Ras]

If you have a 120VA transformer then do not expect more than 120 watt on both channels. It is just not possible.

[pinkmouse]

Originally Posted by ingenieus

The design presented there will work with the 3281/1302 without any changes (the designer said so himself in one of the posts).

It does, I built it.

edit: And slightly cheaper to build than my other project that uses them, my Krellclone.