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Old 26th June 2010, 09:12 AM   #1
BrianVG is offline BrianVG  Belgium
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Default Mosfet IRFP240/9240

Hello everyone,

I have found a low power amplifier with the IRFP240/9240.
At some fora I saw that this design has some problems like the LED and the
cermet trimmer.

Click the image to open in full size.

Thank you.
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Old 26th June 2010, 02:18 PM   #2
balaboo is offline balaboo  United States
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Despite what you have heard, the design will work just fine - make sure the bias current is between 20ma-50ma, and use a nice thick heatsink. I have a similar design as a guitar amplifier that is run at full blast with no thermal runaway issues.
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Old 26th June 2010, 05:28 PM   #3
AndrewT is offline AndrewT  Scotland
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that circuit will work well with Lateral FETs as outputs.
Using Vertical FETs is risking thermal runaway.
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Old 26th June 2010, 09:15 PM   #4
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Quote:
Originally Posted by AndrewT View Post
that circuit will work well with Lateral FETs as outputs.
Using Vertical FETs is risking thermal runaway.
If using vertical FETs keep the bias as low as possible to stop thermal runaway. If the bias is just enough to kill crossover distortion you probably wont even need any thermal feedback to the bias cct.

I have built about 40 amps of a similar design and all have run very well.
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Old 27th June 2010, 01:14 PM   #5
juma is offline juma  Serbia
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I think we have a 100 threads about this circuit - does anyone have an idea how to stop it popping out every month or so...

Yes, it will work and survive with 20mA bias and really big heatsink but it sounds awful - LM3886 is a State of the Art class compared to that missgeburt
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Old 27th June 2010, 01:29 PM   #6
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Quote:
Originally Posted by juma View Post
I think we have a 100 threads about this circuit - does anyone have an idea how to stop it popping out every month or so...

Yes, it will work and survive with 20mA bias and really big heatsink but it sounds awful - LM3886 is a State of the Art class compared to that missgeburt



LM3886 better than that amplifier?

How?
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Old 27th June 2010, 08:06 PM   #7
BrianVG is offline BrianVG  Belgium
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Why would it sound awfull?
I need to make a Mosfet Amp for school, LM3886 is way to easy.
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Old 27th June 2010, 10:24 PM   #8
juma is offline juma  Serbia
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Quote:
Originally Posted by AudioTechs View Post


LM3886 better than that amplifier?

How?
Easy...
Almost everything is better than that insult of an amplifier.



Quote:
Originally Posted by BrianVG View Post
Why would it sound awfull?....
When I was 3 years old I didn't believe my dad that hot stove is not to be touched, I learned it a hard way - although those glowing circles looked so attractive...
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Old 27th June 2010, 11:12 PM   #9
BrianVG is offline BrianVG  Belgium
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I also read that this design is not able to work with the IRFP9240/240.
It has something to do with lateral/vertical. I only did learn how to use a Mosfet as a switch,nothing about lateral/vertical.

Thanks
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Old 28th June 2010, 01:12 AM   #10
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Quote:
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Easy...
Almost everything is better than that insult of an amplifier.
Now, now .... the LM3886, 3875, 4780's et alia in many configurations sound very fine.
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