Old school fosgate amp question

[ashren315]

I have an old school 800a4 fosgate amp that I had in my old truck. I stopped using it and just disconnected it because after awhile of playing music through it, it would get really hot to touch (much hotter than any of the 3 800a2s or the 600a4 I also had in the truck) and start playing this loud screech sound through the speakers it was hooked up to.

I still have this amp and have something new I would like to use this amp on now. Could an improper or undersized ground or power wire have caused it to do that? I had zero gauge running from a bank of 3 batteries that were installed in the bed of the truck with the amp (it had a hard top cover) running to a distribution fuse block and had 8 gauge power wire running from the distribution block in about a 3 to 4 foot run to the amp. The ground was similar. Zero gauge grounded to the frame of the truck running to a distribution block then 8 gauge in about a 3 to 4 foot run to the amp. Each distribution block (ground and power) was responsible for two amps each.

So was it the wiring that was likely causing this or is it something else internal in the amp. It sounded great up to the point where the screeching sound would start. It never shut off or anything but I always turned the power off immediately when it started doing that sound.

Thanks.

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[Boomin_tahoe 5,000+ posts]

Were you running a stupid low impedance?

I think those particular amps just got hot...period. There were many threads of people asking the same question, and yet the amp would not shut off. Just kept playing.

If I were you, and if you do plan to run the amp, get a fan or 2 to blow on it to keep the heat away.

 

[ashren315]

Were you running a stupid low impedance?
I think those particular amps just got hot...period. There were many threads of people asking the same question, and yet the amp would not shut off. Just kept playing.

If I were you, and if you do plan to run the amp, get a fan or 2 to blow on it to keep the heat away.

I was running a set of the FNQ 6.5" components on each channel through the supplied crossover with those sets. The Ohms shouldn't have been a problem.

Like I said, it wasn't just about the heat even though the amp would get too hot to hold your hand to, but also the fact that it would start making a loud screeching soundo through the speakers once it got hot. That sound was all you could hear playing through them when it would do that. I haven't hooked it back up since it started doing that and when I wrecked my truck I just took all the stuff I had in it out and put it away in the garage.

 

[Boomin_tahoe 5,000+ posts]

Might possibly be a bad amp then.

If you can and have the know how or figure it out, see if you can expose the guts. Look for anything weird, discoloration, burnt something, etc.

 

[ashren315]

Might possibly be a bad amp then.
If you can and have the know how or figure it out, see if you can expose the guts. Look for anything weird, discoloration, burnt something, etc.

I did open it up. Didn't notice anything that looked burnt or blown out and I didn't smell anything burnt either.

I know if an amp doesn't get proper grounding or power, it can overheat. I've just never seen one make the noise this one makes through the speakers and it's really odd that when you first turn it on, it plays and sounds perfectly fine through the speakers, but after about 30 minutes to an hour of playing, it would just get really really hot to touch and then the noise would start.

 

[Boomin_tahoe 5,000+ posts]

Getting hot with those amps, sorry to say but that's normal. Even if the proper gauge of wiring was used.

Now as for the noise thru the speakers, unless there was more info involved, I can only guess at this point which could be many factors, i.e. bad grounding, bad RCA's, alt whine, etc.

 

[ashren315]

Getting hot with those amps, sorry to say but that's normal. Even if the proper gauge of wiring was used.
Now as for the noise thru the speakers, unless there was more info involved, I can only guess at this point which could be many factors, i.e. bad grounding, bad RCA's, alt whine, etc.

Guess I need to hook it up again on a test bench and see what it does. Just thought I'd shoot the question here and see what others thought about it.

Thanks for the replies.

 

[Boomin_tahoe 5,000+ posts]

Report back on your findings.

 

[ashren315]

Report back on your findings.

Will do. Just got to find someone with a test bench or temporarily make one of my own.

 

[Boomin_tahoe 5,000+ posts]

Will do. Just got to find someone with a test bench or temporarily make one of my own.

If you do, it comes in handy when buying/selling stuff. And test things right on the spot.

 

[ashren315]

If anyone was curious. I did hook this amp up temporarily today and ran it for about an hour. It ran fine. I only had one speaker hooked to it but it never got overheated or produced any noise. It must have been a power or ground issue in my old truck causing the amp to do that.

 

[kr15 5,000+ posts]

Those amps run hot as is. I bridged my 800a2 at 1ohm years back and it probably could have fired an egg. Wouldnt protect often either

 

[The_Quiet_One 10+ year member]

Several older amps tend to run pretty warm, but if it seems too hot your ground is generally a good place to check.