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blackreplica 28th March 2004 01:31 PM

GC Power Supply Trouble
Hi guys

Today I used the supplied diagram to wire the twin secondaries of my transformer. I measured the AC voltage on the secondaries and got a perfect 25-0-25.

That part's fine. But once I wired the secondaries to the rectifier and turned the power on, I got a terrible mechanical "rrrrrrr" sound and the transformer and rectifier started to get VERY hot in just a few seconds. I'm thinking something must have shorted so I quickly shut it off.

What in the world could I be doing wrong? I even have 2 rectifiers and tried it with both but as long as I connect the marked AC pin to ANY other pin on the rectifier, I get that horrible sound!

The problem is that on my rectifier, only one AC pin and one + pin is marked. The other 2 are not. I assume that the corresponding AC pin is diagonally across from the marked AC pin, and same for the + pin right? Even so, I did try wiring the AC pin to every other pin, but no matter what, that sound/heat persists. The transformer works fine when its not connected to the recitifer and I measure the voltages off the secondaries.

Since then, i managed to get the pin diagram for the recitifer just to make sure i got things right and i did. So i just cant understand whats happening

I dare not go any further until I am able to solve this problem and I hate to ask simple questions like this but i've looked pretty much everywhere and no one has mentioned a similar problem. I even scoured the whole decibel dungeon site and couldn’t find anything that could help my problem.

Hope to get some help, thanks so much

P.S the recitifier is a generic 100V 25A bridge from

SvErD 28th March 2004 01:43 PM

Swap the leads of ONE of your secondaries and everything should be OK.

blackreplica 28th March 2004 01:56 PM

Hi sverd,

are you referring to the AC leads? I think i tried that, but it didnt work either...unless you mean the 0V leads?(its a twin secondary)

Apologies for the confusion

SvErD 28th March 2004 02:18 PM

Yes I mean the AC leads of one of the secondaries. If you could make an accurate sketch of how you've connected everything it would be easier to explain.

blackreplica 28th March 2004 02:33 PM

2 Attachment(s)
Ok i've drawn a rough sketch(attached)

originally, i connected black to yellow(0V) with red and orange going to the AC terminals of the recitifer. Done this way, i get 25V from either of the secondaries to the 0V secondary and 50V from one AC secondary to the other AC secondary. When i connect this to the rectifier, i get that terrible sound and heat

Then i followed your advice and tried to swap one of the secondaries. So now the red and black wire is switched, i.e. red and yellow are joined together(0V) and black and orange are the AC leads going to the rectifier. Done this way, i get 25V from either secondary to 0V but when i measure voltage across the AC terminals, i get a very mysterious 0V AC on my multimeter. When i hook up the rectifier everything seems ok, but i get no DC voltage off the rectifier DC output terminals.

Doesnt seem to be working at all. I'm very disheartened :( any idea what i'm doing wrong?


matjans 28th March 2004 02:36 PM

ok then, to avoid confusion and to prevent anybody from getting killed, the rectifier bridges should be hooked up like this:

I've used the standard (EU?) toroid color coding scheme. If you're not sure, just check the resistance. red-yellow should have some resistance, the other pair too. infinite resistance means you've got the wrong wire (not the same secondary winding)

this should do it...


blackreplica 28th March 2004 02:42 PM

Oh dear,

You mean i need to use both my rectifiers(i originally bought the second as a spare). The colour coding is a little different to the one on my transformer though, how do i interpret it? Is there a way for me to just use one? My transformer has twin 25V secondaries. I'm aiming to get 25V AC to 36V ac for the rails of the amp(my gc will be the LM3875 version)

BTW i hope my nick doesnt offend. I got an email once from a guy who asked me to change it but i think people misunderstand, its actually a tongue-in-cheek kinda name, not meant to offend or anything. Maybe thats why hardly anyone helped me in my earlier threads:o :D

Just to update:

I have tested the leads as mentioned in the above post for resistance. I have found the matching secondaries and tried wiring them to the rectifier AC terminals again as explained in the diagram above. It made that sound/heat again!!! What in the world...??

matjans 28th March 2004 03:07 PM

don't forget to use a fuse in front of the toroid, that might make it a little safer...

i can't reccomment using only one bridge, i've tested it and somehow it degrades the sound. makes it sound very dull.

what are the rectifier's specs? are you shure you haven't blown them up in previous attempts to get a working bridge ?

25v secondaries will, after rectification provide you with ~35V DC.

(ans yes, i think your nick might be the reason for not getting too much help on these fora)

Devil_H@ck 28th March 2004 09:56 PM

Well, I had some fun with a toroid today...
I soldered one diode on my PCB the other way 'round. When I turned on the power to test/calibrate the output voltage I got a nice buzz and stinking smoke :). Be sure to check your diodes again!

blackreplica 28th March 2004 11:47 PM

hello everyone,

Is there a way to check with a multimeter if the rectifier is spoilt? I have subjected the bridges to that buzzing/heat many times but never more than a few split seconds at a time. I never saw any smoke or heard any explosions thus far(basically from the exterior, nothing seems to be burnt)

The rectifier i am using is this one:

I have 2 of them at this point.

Just to recap, i tried to wire it the way matjans described in his post diagram but the buzz/heat persists.

Really appreciate any help!

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