Old school audiobahn a4125hct

I just got this amp and cleaned up the inside a LOT and it works good but there is a high pitch whine coming from the 4 caps in the center and when I touch them it goes away, will replacing them solve this? They are 4700uf 50v 85C* . Should I replace with higher rated? Obviously 105C but I see a lot of people use higher uf rated.
 

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Oldskoolamps

Member
2016-01-27 12:35 am
I took the PSU Fet clips off and found a few of them kinda cracked and bulging. They are irfz44n, I have a some left from a JLaudio amp I repaired but I only have 6. There are 5visibly damaged FETs, there are 16 total in the PSU. I know when they go bad you're supposed to replace all, but in this case it was working. Do I have to replace them all? Also I have an A1500HCT and the FETs in that are irfz48v? I'm almost positive. Should I upgrade to the higher rated 48v's or the 44n's??
 

Perry Babin

Member
Paid Member
2003-11-20 11:01 am
Louisiana
www.bcae1.com
For the amp to be reliable, all of the FETs in each bank (four banks of 4 FETs in this amp) need to match. If you have 5 that failed, it means that at least one in a second bank failed. All 4 of those need to match.

If this is your amp, you can do whatever you want to do with it. If it fails, you're the only one inconvenienced. If you're repairing this for a paying customer, buy the FETs you need to have them match.
 

Oldskoolamps

Member
2016-01-27 12:35 am
The amps are mine. My main question being will the will the 48v's work in place of the 44n's? And would they be more reliable or in any way superior since the irfz48v are rated at 60v 72a and the irfz44n are rated 55v 49a? I'm ordering 20 today so they will all be matched, its only $12 or $15.
 
Ebay has a reputation (for good reason) for selling counterfeit and second rate parts. Buy from reputable distributors like Mouser or Digi-key.

If the terminal is actually what's producing the heat, the amp is either drawing excessive current or there is a loose connection at the terminal block (either on the board or at the wire connection point).

There is one gate resistor per gate terminal (and one gate terminal per FET).
 
I want to go with the 48v, the resistors look rough anyway. Here are some pics, what should I replace them with? Im trying get a list to get my order in today.
 

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oh ok, posted just as you answered. I am reading those pages and they are very helpful i have been trying to learn the past couple months to much success. here are some better photos as i found it very difficult to find pics of these amps. is it just those 2?
 

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