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covik 5th November 2006 04:50 PM

The Smallest 50w Mosfet Amplifier
2 Attachment(s)
I think it is a smallest mosfet (hexfet) amplifier i have ever seen

It is a 50W on 4ohms 30-0-30Volts.

Im trying to build it but i must design the PCB first.

Tell your opinion!

Bye bye!

AndrewT 5th November 2006 05:15 PM

what makes you think this is small?

or do you mean few components?

I don't think it sets any records based on the posting so far.

lineup 5th November 2006 06:54 PM

Re: The Smallest 50w Mosfet Amplifier

Originally posted by covik
I think it is a smallest mosfet (hexfet) amplifier i have ever seen
It is a 50W on 4ohms 30-0-30Volts.
I'm trying to build it but i must design the PCB first.

That is the most simple way to build a power amplifier
with some normal watt output.

Important is to place those diodes, so they can sense the temp from heatsink
- somewhere close to those HEXFET.

Myself would not use HEX MOSFET.
Instead I would use for example 100 Watt MOSFET pair, 2SK1058 ( 600pF ) + 2SJ162 ( 900pF ).
They cost more, but are more temperature safe and easier to drive.
Quality components has got a price,
but they make very simple designs have a fair chance to perform better

If you use HEXFET maybe IRF640 ( 1300pF ) + IRF9640 ( 1200pF ) would be a suitable option?

What did you have in mind?


AndrewT 5th November 2006 07:10 PM

there is a slight problem with the small FET option.
Both vertical and lateral will require substantial quiescent bias and thus need bigger heatsink than if BJTs were chosen for output devices.

I have not done a count but how many components in a JLH? and it's guaranteed to sound good.

jaycee 5th November 2006 07:46 PM

Surely the diode based temperature compensation should be dead and buried these days - a BD139 makes a good VBE multiplier and it is cheap.

I've never liked the idea of using MOSFETS without drivers... loading the VAS directly has never seemed good to me... but I don't know much about MOSFET based amps :)

mikeks 5th November 2006 08:28 PM


Originally posted by jaycee
... loading the VAS directly has never seemed good to me...

Good Man!

john_ellis 5th November 2006 08:43 PM

Hi Jaycee

Wouldn't a similar MOSFET (to the output devices) be better than a bipolar in a MOSFET o/p stage?


covik 5th November 2006 09:29 PM

The components for 50W
2 Attachment(s)
Sorry people.
I forgot the components table and here it is word file.

Yes, you think is better to use mosfets but i must tell you that this schematics is from an italian kit called "Nuova Elettronica" and it is an amplifier tryed out and well balanced, so wrote those one from "Nuova Elettronica".

I have no PCB and no description but i have the schematic, components table and i ready bought the coponents at 1995. year when i was at secondary school and i dont know if they will work (coponents are brand new but from 1995).
At the same time i made the TDA1514A 50W amplifier (stereo version with 2 amplifiers) that is still working so i have forgotten this one with hex and i would try it.

OK people lets make it work!!!
Thank you!

lineup 5th November 2006 10:02 PM

hi again

Using HEXFET for linear Audio applications.

There are so many topics on trying to use these comparatively low priced HEX MOSFET
instead of somewhat higher quality LATERAL MOSFET,
which are more intended for good audio applications and cost more.

Of course The One and Only has contributed to this quite a bit.
At this forum.
The difference is that he often use them in Class A operation,
and he sure has got the knowledge how to handle them optimally

All data, knowledge and reading of investigations and findings of others
can help bringing about some bits of more understanding
what to think about when using these intricate devices called HEXFET.
Not only make use of them,
but to try to make best possible audio amplifiers with them in circuit.

lineup, november 2006


So here is a contributed article article and a collection of thoughts from ......
..... yeah, once again: Rod ' ESP ' Elliott

Searching the web for some HEXFET information / amplifiers
I once again ended up at his terrific audio web collections.


Using HEXFETs in High Fidelity Audio
Mitch Hodges

Edited and Updated by Rod Elliott (ESP)
Last Update: 13 March 2006

4 - References
The following are all PDF files, and are direct links to the International Rectifier web site ...

AN-936 application note, The Do's and Don'ts of Using MOS-Gated Transistors
AN-937 application note, Gate Drive Characteristics and Requirements for HEXFET
AN-941 application note, Paralleling HEXFET power MOSFETs
AN-944 application note, Use Gate Charge to Design the Gate Drive Circuit for MOSFETs, IGBTs"
AN-948 application note, Linear Power Amplifier Using Complementary HEXFET Power MOSFETs
:cool: :cool:

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Lineup Audio Amplifiers

boraomega 5th November 2006 10:22 PM

2 Attachment(s)

I think it is a smallest mosfet (hexfet) amplifier i have ever seen
Just for fun... 3 semis... 50W... 0,1%

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