The Smallest 50w Mosfet Amplifier

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ok PEOPLE!
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!
 

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covik said:
ok PEOPLE!
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.

Okay.
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?


Regards
lineup
 
Hi,
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.
 
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 :)
 
The components for 50W

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!
 

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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 sound.westhost.com ' 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: http://sound.westhost.com/articles/hexfet.htm :cool:

Articles Index:
http://sound.westhost.com/articles.htm
Website:
http://sound.westhost.com/


lineup
Lineup Audio Amplifiers
http://lineup.awardspace.com/
 
I think I have wrote about this many times before...

Regarding the use of HEXFETs as output transistors, there is really no reason to suppose they are inferior than the 'made for audio' MOSFETs. As with all components, the trick to making good use of them, is how they are used.

Some things to remember:
'Made for audio' MOSFETs are primairly optimized to give good complementary performance. It is known in advance what the complementary pairs are, they were designed that way. The key thing here is that to get good complementarity of the P and N part, the construction of the respective parts has to be quite different. In other words, finding HEXFETs with good complementarity is NOT a matter of just using IRFxxx and IRF9xxx, xxx being the same number in both the P and N part! You have to do a bit more work there.
Lateral MOSFETs are often quoted as having lower Ciss. However, using them in an amplifier only on that merit, is irresponsible. The reason is, how much of Ciss actually figures as a load for the previous stage, depends on how it is divided between Cgs and Cgd, and, much more so, on the MOSFET's gm. It should be noted that lateral MOSFETs have fairly low gm compared to HEXFETs and even PIMOS (Toshiba audio MOSFETs) - in fact, what is important here is to look at Ciss/gm. This is a relatively constant number for a given MOSFET technology, and it is in fact HIGHER for laterals, which is not desirable. On the other hand, laterals have slightly less pronounced Ciss nonlinearity, and, which is usually more important when it comes to parts substitutions, their thermal coefficient changes from positive to negative at usably low currents (about 100mA) so for bias currents close to or above 100mA, no thermal compensation is necessary. The parts cost savings due to this are usually negative, because the laterals cost much more than HEXFETs with the necessary thermal compensation components.
'Made for audio' MOSFETs are few in type and much more difficult to get than HEXFETs, which, in turn, are easily available, although the best choices may require a bit more work to get. With the former, the choice of maximum current is limited to 4 basic parts, it is much better with HEXFET and similar parts.
To sum things up: the choice of the tool is no guarantee the work gets done, the skill with which it is used plays a major part :)
 
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