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Old 25th March 2016, 01:57 AM   #1
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Default 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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Old 25th March 2016, 02:03 AM   #2
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Are you sure that the noise isn't coming from one of the transformers?
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Old 25th March 2016, 02:17 AM   #3
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When I touch them it goes away
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Old 25th March 2016, 02:22 AM   #4
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Them?
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Old 25th March 2016, 03:10 PM   #5
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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??
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Old 25th March 2016, 03:58 PM   #6
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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.
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Old 26th March 2016, 07:00 PM   #7
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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.
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Old 26th March 2016, 07:16 PM   #8
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The Z48s will work but you should reduce the gate resistor value if the originals are 100 ohms. The 100 ohm may be marginal. I'd go down to 68 ohms at least. You wouldn't need to go below 47 ohms. Don't buy the FETs from ebay.
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Old 26th March 2016, 11:21 PM   #9
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1 What all would happen if you failed to change the resistors (these are 1k? brown black red gold)? Would the pos terminal get hot? 2 Where should I buy them? What exactly is different with ebays?
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Old 26th March 2016, 11:23 PM   #10
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Nvm the gate resistors are 1 per group right? They are 100
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