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Rockford 800a2 outputs
Rockford 800a2 outputs
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Old 15th March 2019, 04:11 PM   #1
imraneesa is offline imraneesa
diyAudio Member
Join Date: Apr 2016
Default Rockford 800a2 outputs


Can i substitute IRF640 with IRF640N?

like i will be using IRF9640 and IRF640N.

can i substitute power supply fet P75N05HD with IRFZ44n with gate resistors as 47ohms?
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Old 15th March 2019, 05:17 PM   #2
caraudioguy2100 is offline caraudioguy2100
diyAudio Member
Join Date: Aug 2010
Some Rockford amps do not like the IRF640N they will cause problems .

Iíve always used the IRF640 and 9640 non N suffix .

And the IRF3205íS with 47 ohm gate resistors will work better in this amp Iím
Not sure the Z44ís will survive .

If Iím wrong someone please correct me
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Old 15th March 2019, 06:11 PM   #3
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
Location: Louisiana
In virtually every Rockford amp that uses the 494 driver IC and FETs in the power supply, the IRF3205s work well. The gate resistors need to be 51 ohms or less. If all of the originals survived and are 51 ohms or less, you can leave them. If only a few of the gate resistors failed, you can just replace the ones that failed with the same value. Some people go with all 47 ohm gate resistors. That's OK but if the value is lower than 47 ohms, it's OK to go back with the original values also.

I've never tried the 640N. The 540N causes various problems in some of the smaller amps. Use what was in it originally, from a reputable distributor. These FETs are stressed hard in these amps and must be the best available (not ebay) unless you want to do the repair again.

Clean out all of the old compound and replace with Dow 340 or equal.
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