Fosgate 801s This is a Good One

[Brain Fried]

Perry This question for you i just pick up a fosgate 801s its been repaired **** poor job by the way and they replaced the IRF640 with IRFB31N0D when i look them up it said they are for power supply but the amp is playing no distortion should i replace them with the right ones? or will these work well in place of the IRF640?

[Perry Babin]

If you have an oscilloscope, look at the waveform on the speaker terminals. If the waveform is displayed as a sharp clean line (not a fuzzy looking line, as it would be if there was low level oscillation) and the amp produces clean audio rail to rail without going into protection, they are probably OK. If there is any oscillation or it's going into protect mode, for an unknown reason, replace them. It's almost always best to use the exact replacement part but if they're in there and they're working perfectly, there's really no reason to replace them.

[Brain Fried]

Originally Posted by Perry Babin

If you have an oscilloscope, look at the waveform on the speaker terminals. If the waveform is displayed as a sharp clean line (not a fuzzy looking line, as it would be if there was low level oscillation) and the amp produces clean audio rail to rail without going into protection, they are probably OK. If there is any oscillation or it's going into protect mode, for an unknown reason, replace them. It's almost always best to use the exact replacement part but if they're in there and they're working perfectly, there's really no reason to replace them.

I don't have oscilloscope yet I am just going to replace them with the right ones this amp is a mess missing all the screws for the board and some missing for holding the mehsa board this is going to a fun one

[Perry Babin]

Replace the mismatched 0.1 ohm resistors also. They need to be matched as closely as possible. THESE are the ones I'd recommend you use.

Since the 0.1 ohm source resistors opened previously, check all of the 100 ohm and 39 ohm resistors connected to the source resistors. You'll need to remove the source resistors (or at least desolder one leg) to get accurate readings.

[Brain Fried]

Originally Posted by Perry Babin

Replace the mismatched 0.1 ohm resistors also. They need to be matched as closely as possible. THESE are the ones I'd recommend you use.

Since the 0.1 ohm source resistors opened previously, check all of the 100 ohm and 39 ohm resistors connected to the source resistors. You'll need to remove the source resistors (or at least desolder one leg) to get accurate readings.

Checking everything the first thing i did and fixing the last gays horrorable soldering job and i still have alot of the 0.1ohm resistors i bought a 100 of them on my lost order after this one i will have 20 left.

[Brain Fried]

well i put that channel under a 2ohm load to a Kicker L7 '15in using a 50Hz 0db test tone and it failed so replace all the IRF's and the A06 & A56 now it can take a beating. Here a couple pictures

The Junk


Much Better

[Perry Babin]

In many of the large Rockford amps, it's extremely important that you replace the driver transistors when the outputs fail. If one is leaky (something that's difficult to detect while the transistor is in the circuit), it will blow the outputs as soon as the mute delay ends. The outputs aren't biased on until the end of the delay and with the huge bank of capacitors, there's no way for the fuse to blow or a current limiter to protect the amp. It simply blows the outputs.

[Brain Fried]

I started on the Heat Sink today

Before


Second coat of paint


After some sanding and polishing it will look like this one