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Old 27th May 2009, 02:53 PM   #1
xcicc is offline xcicc  Italy
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Default new ampli with IRF240

Hi, I just finished assembling this amplifier based on this project.
http://www.redcircuits.com/Page100.htm
I plugged it all but feel the music just croak the mosfet fortunately no heat and no feel smell of burning.
On series of 220v I connecteda 220v 60W light bulb to limit the current, turning the trimmer does not change anything ...
any ideas?
thanks

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Old 27th May 2009, 04:32 PM   #2
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Default can you draw a schematic ??

to see how this is working ????
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Old 27th May 2009, 04:32 PM   #3
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The most obvious thing is r14/15, those should be .33 ohm ,not 33R. Nice hand made layout , thought I was only one who did that (besides carlos - DX).
OS

edit: another issue, even if you get it to amplify with the resistors,the circuit calls for lateral mosfets(it lies!!). All is not lost , you could make a small daughtercard with cap, 2 resistors, trimmer and Bd139/mje340 to give thermal stability.
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Old 27th May 2009, 05:42 PM   #4
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Quote:
Originally posted by ostripper
The most obvious thing is r14/15, those should be .33 ohm ,not 33R. Nice hand made layout , thought I was only one who did that (besides carlos - DX).
OS

edit: another issue, even if you get it to amplify with the resistors,the circuit calls for lateral mosfets(it lies!!). All is not lost , you could make a small daughtercard with cap, 2 resistors, trimmer and Bd139/mje340 to give thermal stability.

I agree tomorrow will replace these resistors, although I think that is not the only error.
thanks
A.
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Old 27th May 2009, 05:52 PM   #5
AndrewT is offline AndrewT  Scotland
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the parts list is wrong.

Do not reduce the source resistors just yet.
You may damage the output devices if you can get sufficient current to turn them on.

The circuit shown in the schematic is designed to ONLY suit Lateral MOSFETs.
It MUST be REDESIGNED to suit Vertical MOSFETs.

Have alook at Vgs for the irf240 and irf9240 that you have fitted.
Now measure the bias voltage you are applying across the gates.
It will not work as is, because the wrong devices have been listed in the parts list.
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Old 27th May 2009, 05:56 PM   #6
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Quote:
Originally posted by AndrewT
the parts list is wrong.

Do not reduce the source resistors just yet.
You may damage the output devices if you can get sufficient current to turn them on.

The circuit shown in the schematic is designed to ONLY suit Lateral MOSFETs.
It MUST be REDESIGNED to suit Vertical MOSFETs.

Have alook at Vgs for the irf240 and irf9240 that you have fitted.
Now measure the bias voltage you are applying across the gates.
It will not work as is, because the wrong devices have been listed in the parts list.

want to say that this amp will not work ever?
I did not understand what I should do, change what?

I also have a doubt about diode 1n4007 and LED
I fear that I have mounted on the contrary.
thanks
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Old 27th May 2009, 07:20 PM   #7
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Andrew is right , for the IRF's a major redesign would be in order , a proper active Vbias circuit + driver stage would be needed. take a look at the quasi line of DIY amps , they use just IRFP240's , but they are proven designs.

Power amp under development

For what you have made, besides the resistors , just jumper the led and diode , leave the trimmer , use 2SK1058/2SJ162 lateral's.

Attached is a similar Op stage to yours the way it should be. (really works).
OS
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Old 27th May 2009, 07:25 PM   #8
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Quote:
Originally posted by ostripper
Andrew is right , for the IRF's a major redesign would be in order , a proper active Vbias circuit + driver stage would be needed. take a look at the quasi line of DIY amps , they use just IRFP240's , but they are proven designs.

Power amp under development

For what you have made, besides the resistors , just jumper the led and diode , leave the trimmer , use 2SK1058/2SJ162 lateral's.

Attached is a similar Op stage to yours the way it should be. (really works).
OS

I do not understand what the project is completely wrong? will not work ever? in other words this ampli whith mosfet IRFP240/9240 can not be built?
with your modification you've redesigned everything.
I do not understand why I have to add another 2 mosfet
or your changes are only to improve?

thanks
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Old 27th May 2009, 07:56 PM   #9
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I've already done this with small IRF640 and 9640, it becomes quite warm at full output, and sounds excellent! I uses it as guitar amp, this must be one of the best designs, pretty simple, no distortion... cool!
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Old 27th May 2009, 08:06 PM   #10
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Quote:
I do not understand why I have to add another 2 mosfet
That was just to show you the "way" , you don't have to use 2 pairs of devices!!

IRF's increase current with heat , so they need something to negate this effect. With a HUGE heatsink , you might get away with it.

Slideman uses the to-220 irf's , they would work with a huge HS, but the big 240's would soon go into runaway.
.
OS
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