![IMAGE_073[1].jpg](/community/data/attachments/166/166384-8d21489ae39836bf7758994cd87911dd.jpg)
Does the amp work properly other than the noise?
Some amps have noisy transformers. It doesn't really indicate that there's a problem. Do you smell anything burning or see any arcing?
If you push/pull/twist on the inductors and transformers, does it make a difference? You should have nothing larger than a 15 amp fuse in the amp and all semiconductors should bee tightly clamped to the heatsink when you do this.
Some amps have noisy transformers. It doesn't really indicate that there's a problem. Do you smell anything burning or see any arcing?
If you push/pull/twist on the inductors and transformers, does it make a difference? You should have nothing larger than a 15 amp fuse in the amp and all semiconductors should bee tightly clamped to the heatsink when you do this.
![IMAGE_074[1].jpg](/community/data/attachments/166/166461-71353eb417a7f258c006ead9688d399e.jpg)
There have been two instances where people were having trouble with an amp using ebay 31N20s and doing nothing more than replacing them with 31N20s from a reliable distributor solved the problem.
I compared them by driving three 31N20s in a circuit. One was from ebay. The other two were from different batches but from a reliable distributor. The two from the reliable distributor appeared to be identical when their traces were laid on top of each other on the scope. The one from ebay was significantly different.
I even compared it to a 42n20 which looks different than the good 31N20s. The ebay 31N20s were even more difficult to drive than the 42N20s. When I say 'harder to drive', I mean that the slope on the rising and falling edges of the waveform was less vertical.
I broke open one of the ebay 31N20s and one of the ones from Future and internally, they appeared identical. The casing was slightly different. The markings on the ebay 31N20s were not printed in precisely the same position on every transistor. It was like they weren't securely held when they were being printed. The printing on the ones I have was in precisely the same position on the face of the transistor (or too close for me to tell the difference with a magnifying glass).
I've been buying mine from Future Electronics and have never had a problem with them.
Well... that's what I know about them. I don't know if they're counterfeit but they're different enough that they won't work in some class D amps.
I compared them by driving three 31N20s in a circuit. One was from ebay. The other two were from different batches but from a reliable distributor. The two from the reliable distributor appeared to be identical when their traces were laid on top of each other on the scope. The one from ebay was significantly different.
I even compared it to a 42n20 which looks different than the good 31N20s. The ebay 31N20s were even more difficult to drive than the 42N20s. When I say 'harder to drive', I mean that the slope on the rising and falling edges of the waveform was less vertical.
I broke open one of the ebay 31N20s and one of the ones from Future and internally, they appeared identical. The casing was slightly different. The markings on the ebay 31N20s were not printed in precisely the same position on every transistor. It was like they weren't securely held when they were being printed. The printing on the ones I have was in precisely the same position on the face of the transistor (or too close for me to tell the difference with a magnifying glass).
I've been buying mine from Future Electronics and have never had a problem with them.
Well... that's what I know about them. I don't know if they're counterfeit but they're different enough that they won't work in some class D amps.
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