Memphis 16-ST1000D Question

[spooney]

Just decided to open up my Memphis 16-ST1000D that I have been using for over a year to finally replace that missing power on LED thats been bugging me ever since I acquired the amp. After finally getting a chance to get the board out of the sink I can see that it has been repaired previously. Looks like the power supply had a nice blowout. There are a few charred spots remaining on the board that acetone won't even touch. Anyway I noticed the ps fets were IRFZ44N's . If I remember correctly the amp used IRF3205's originally. I haven't had any problems with the amplifier but I imagine that if I replaced the IRFZ44N's with IRF3205's that I would make the amplifier more reliable. Is this a worthwhile venture or am I wasting time and money with this swap?

 

[spooney]

After looking at the data sheet for the IRFZ44N it would seem that the amp can't possibly be doing rated power with these fets in the power supply unless I am missing something. It says the max power dissipation on these is 94 watts . Does that mean that 94 watts x 8 power supply fets = 752 total watts the power supply could produce?

 

[Perry Babin]

The power dissipation rating on the power supply FETs has nothing to do with the output power. It tells you how much power they can dissipate at a given temperature. In switch mode operation, they dissipate virtually no power because they're either completely on or off.

If these have been 100% reliable, you may not need to replace them. The increase in output power will be absolutely inaudible.

 

[spooney]

Thanks Perry. That clears up something I've always wondered about the dissipation rating. I've run the amp at one ohm for over a year so I think the fets that are in there are doing their job well. If it fails I know what to replace them with. Is the dissipation rating something to consider when looking for output fets.

 

[Perry Babin]

For switching amps (class D, T...), it's not really important because when operating normally, they're fully on or fully off and therefore the power dissipation is minimal. For linear (not the brand Linear) amps, it's much more important but it's not the only thing you have to look at when selecting replacement parts.