I noticed that with my home built Aleph 3, one of the output mosfets (not the current source mosfet) is much hotter than the others. I had matched the mosfets, but evidently did not do a good enough job.
The solution is to take the mosfets out, and put in a better matched set of mosfets....But in the mean time, is there anything I can do, like changing a resistor, to make the output mosfets share the load better?
I'm afraid that running the amp the way it is, will cause a failure in the hot mosfet leading to DC current finding its way to the speakers causing an expensive accident.
Any advise is greatly appreciated....
The solution is to take the mosfets out, and put in a better matched set of mosfets....But in the mean time, is there anything I can do, like changing a resistor, to make the output mosfets share the load better?
I'm afraid that running the amp the way it is, will cause a failure in the hot mosfet leading to DC current finding its way to the speakers causing an expensive accident.
Any advise is greatly appreciated....
audionut said:
Have you checked the values of your source resistors connected to the output devices, are they fairly close in tolerance? Have you compared the value of the voltage over the source resistors? They should all be the same.
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Brian
You don't say how much hotter. I suggest that you
measure the DC voltage across the source resistors
of all the Mosfets and report back.
measure the DC voltage across the source resistors
of all the Mosfets and report back.
You could match the MOSFETs under conditions closeraudionut said:
to the working condition they will operate UNDER
Otherwise you can measure and adjust
until they fits fairly good together
as the boys already have told you
this is my any advice
a lot of good ideas, not only my idea
but Nelson and the others, in the thread
here, I searched and found him
an old technique
there are several schematics
ask before you use them, just in case
Nelson's will work safely to 100%
matching of mosfets
there are several schematics
ask before you use them, just in case
Nelson's will work safely to 100%
FUZZY on Matching FETs
The hot mosfet is quite a bit hotter than the others...On its source resistor I measured a voltage drop of .95v the other resistors had voltage drops of around .45v. I measured the current going through the hot mosfet and it was 1.75amps while the other mosfets measured around 1 amp.
Until I rematch the mosfets, is there anything I can do to bring the current draw down for this one mosfet?
Until I rematch the mosfets, is there anything I can do to bring the current draw down for this one mosfet?
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