LM3875 gainclone help!!!

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Hello all,

I recently put together a gainclone amplifier from Peter Daniel's website. Obviously it doesn't work. I did everything exactly as instructed, except the chassis ground is not connected (CHG). There is no sound whatsoever coming from the amp and the 4 inner diodes in the power supply are extremely hot compared to the other diodes. When I disconnected the PS from the amp, 35 Volts were passing between V+ and V-. I have attachted (high) quality pictures of the front of the amp. If anyone knows what is wrong with it, please help!!!
 

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Carefully measure pin 1 on the lm3875 from ground and you should get +35, then measure pin 4 you should get -35 Volts there, careful not to slip and short anything though, it's easy to slip as I found out....

Also, do you have a heatsink connected? That was my problem everything was hooked up correctly, but the heatsink I had was not up to the task, so all i'd get was very quiet distortion, that would cut in and out, and no sound whatsoever if I had no heatsink hooked up, which was evidently the chips protection kicking in. Might be the problem, I didn't see a heatsink in the pics.

Good luck!
Tristan
 
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Joined 2007
I think for your own personal safety you should spend a little time educating yourself about these things before you proceed. It doesn't sound like you have a very good grip on what you are doing. Can be dangerous and expensive. You will enjoy your amp a lot more when it is working properly and you know a little bit about how it works.
 
I assume you've got dual secondaries now.
Do they meassure about the same when not attached to the board?
Look at the datasheet for the trafo, if there are markings on 2 of the four AC inlets on the pcb, then you should connect the secondaries with dots or other marking in the datasheet to the inlets on the pcb with markings. And unmarked to unmarked, keeping the seconadaries paired.

Wow, I hope I made any sense at all, sorry for my poor english.

And follow the advice to learn first, solder second. I'm relatively new at this myself and have learned the hard way. It's faster and easier to study first and do it right, than to go by trial and error, not to mention cheaper.
 
I was going to buy a transformer with dual secondaries, but they look very expensive (>$50). So I read up on the power supply options on audiosector.com and found out that two separate transformers could be used. I have lots of those laying around, so my question is how close do the two have to be in voltage. The closest two I have are 24 and 24.2 Volts. Will that work?
 
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