IRFP240/IRFP9240 Power amp

[jmateus]

Mike,

That bad, hein?
I was thinking using 240 & 9240 but again the 162 & 1058 are not
out of question.

However the Vbe multiplier wasn't under my plans but is something that can be added. The only problem here is I already build the boards
I guess the whole plan has to be scrapped, unless there is some other
remedy.

Things have been so bad for me lately that any project of mine
hasn't worked properly. I think I'm going to sleep for a good while
before I decide to build another amplifier. Period.

[MikeB]

John, it's just that you can't expect any reliability and very high quality from that circuit. It will distort trebles as hell.
But, if you already have made the boards, why not finishing and trying ?

Mike

[lineup]

Originally posted by jmateus
However the Vbe multiplier wasn't under my plans but is something that can be added.

If you use 2SK1058, it might work like it is.
As they are LATERAL MOSFET.
And for one other special reason, unusual high value emitter resistors.
0.33 ohm is a bit more than usual, and will make better control of bias in output stage.
I would however suggest sufficiently BIG heatsink to be used,
to reduce heat as much as possible.


You can compare with an almost identical power amplifier,
using lateral mosfets, from a book edited in London 1991.
I wouldnt be surprised if what you want to build
is a variation constructed from this 1991 MOS amp.
See attached schematic.

Two details that differ.
The C7 - R8 filter. Some sort of compensation for better performance.
The LACK of emitter resistors in output stage.

Enjoy an old amplifier from a designer that has written several books
with all sorts of transistor audio amplifiers as well as most every kind of audio circuits.

Regards
lineup

[JojoD818]

Thanks for all the replies!

Can I use the 240/9240 devices on the schematics that were posted? Simple drop-in?

TIA

[Wavebourn]

Originally posted by JojoD818
Thanks for all the replies!

Can I use the 240/9240 devices on the schematics that were posted? Simple drop-in?

TIA

Yes. And don't try high bias current, you don't need it at all except following by some beliefs.

[djk]

"Can I use the 240/9240 devices on the schematics that were posted? Simple drop-in?"

I didn't see a schematic that had temperature compensation for the bias. I am not normally a betting man, but I would wager that you will have problems unless you take care of the bias.

Nelson Pass makes it work by running it in class A with the necessary large heatsinks, and even his amps like the A75 have a bias transistor.

[lineup]

Originally posted by JojoD818

I have some IRFP240/IRFP9240 leftovers from an F1 project, I was hoping I can build a simple class ab amp out of a single pair. Power output is not an issue as long as it sounds good. Any schematics would be appreciated.

Originally posted by luixssj3
I build this and it work...

If you build one too let me know your opinion...

Originally posted by JojoD818

Can I use the 240/9240 devices on the schematics that were posted? Simple drop-in?

JojoD818 and JMateus

Of course you can use IRF240 / 9240 HEX MOSFET in a power amplifier.
They are good transistors, used in the correct way.
But they have a different temperature caracteristic than 2SK1058 or other LATERAL MOSFET

There are many topics, if you search for lateral in this forum!


The solution how to properly use HEXFET and BIPOLAR compared to LATERAL MOS
is to use a good temperature sensor transistor at the heatsink.
Also called VBE-Multiplier.


In the simple mosfet schematic
http://users.swing.be/edwinpaij/imag...lisimpleV2.gif
a plain trim potentiometer resistor P2 may not be able
to control the output 240/9240 HEXFET.
There is a risk for thermal runaway.
This is like when a train out of of control goes downhill
- it will only go faster and faster ... until .... .... .. smoke and fire
--------------------------------


Nelson Pass helped to advice in topic started by luixssj3.
You can see howto do this temp control, in the schematic
showing a part of a Nelson Pass amplifier ( A75 )
in this post by me:
http://www.diyaudio.com/forums/showt...61#post1011461

To understand this issue,
to see how we can use IRFP240 / IRFP9240 with proper temp compensation
you may read the whole topic with discussions:
Simple MOSFET amp problem


Regards
lineup has got a temperture of 37 degrees,
thermal runaway is called fever and will cause his death at 42-43 degrees
if not properly controlled by his organism

[ilimzn]

Originally posted by Wavebourn

Yes. And don't try high bias current, you don't need it at all except following by some beliefs.

The thermal drift of MOSFET threshold voltage is not subject to 'some beliefs' but to physics. So, unless you try it with zero bias, suggesting to those that are trying to learn that VMOS, DMOS, HEXFET and other similar MOSFET topologies are direct drop-ins for lateral MOSFETs as used in most of these schematics, without any other changes is irresponsible, to say the least. You are lucky I am not a moderator here because IMHO this would be cause for a ban. To make it worse, posts like this continually perpetuate this disinformation.
Is this a flame on my part? Not really - I would suggest that you try yourself what you are suggesting to others, and there will be flames enough.

[JojoD818]

Originally posted by lineup




JojoD818 and JMateus

Of course you can use IRF240 / 9240 HEX MOSFET in a power amplifier.
They are good transistors, used in the correct way.
But they have a different temperature caracteristic than 2SK1058 or other LATERAL MOSFET

There are many topics, if you search for lateral in this forum!


The solution how to properly use HEXFET and BIPOLAR compared to LATERAL MOS
is to use a good temperature sensor transistor at the heatsink.
Also called VBE-Multiplier.


In the simple mosfet schematic
http://users.swing.be/edwinpaij/imag...lisimpleV2.gif
a plain trim potentiometer resistor P2 may not be able
to control the output 240/9240 HEXFET.
There is a risk for thermal runaway.
This is like when a train out of of control goes downhill
- it will only go faster and faster ... until .... .... .. smoke and fire
--------------------------------


Nelson Pass helped to advice in topic started by luixssj3.
You can see howto do this temp control, in the schematic
showing a part of a Nelson Pass amplifier ( A75 )
in this post by me:
http://www.diyaudio.com/forums/showt...61#post1011461

To understand this issue,
to see how we can use IRFP240 / IRFP9240 with proper temp compensation
you may read the whole topic with discussions:
Simple MOSFET amp problem


Regards
lineup has got a temperture of 37 degrees,
thermal runaway is called fever and will cause his death at 42-43 degrees
if not properly controlled by his organism

wow! thanks for the links... looks like I have a lot of catching up to do.

so this schematic from luixssj3: http://img55.imageshack.us/my.php?image=misurevx3.gif should be a good place to start?

[jmateus]

luisxssj3

In fact this schematic makes much more sense, is this something that
could be implemented with IRFP240 and IRFP9240? I really don't
know the difference between vertical and lateral mosfets, well to
be honest I don't much about fets in general, this is why I never bother to build any amplifier but with bjt's. Only years ago I built an
amp from Slone with Mosfets that gave me no problem at all to
construct. It worked at first, the only problem is I don't like its sound
it seems too compressed and without life.
Since then I concentrated only in BJT's and no Mosfet amplifiers deserved my attention. May be I'm being prejudice and there are
quality desgins but I don't know. My slone's Mosfets (1058 & 162) is
not up to quality I was expecting.

Can someone atest of the quality of this design? See, I'm only a builder and listener not too able to evaluate an amplifier by it's
design.