LM1875 - need help

[bamera]

My problem is simple I hope. 

I´m using a +/- 18V 3A transformer with a full wave rectifier bridge (1N5408 diodes) and 10000uf smoothing capacitors as my power supply. I tested it with the TDA2050 PDF split supply application circuit through an 8ohm 200W speaker and it sounded great, no problems at all.


I decided to try the Lm1875 split supply circiut from the PDF. I put it together exactly like the schematic and tested it, it worked perfectly (excellent quality sound) for about 10 seconds and shut down.
I tried again and the same thing happened.

The problem is that my heatsink is quite large and gets barely warm so I can´t see this as temperature issue. I used arctic silver thermal paste for further testing and still the same problem. I had the same exact problem with the LM3886, after two circuit builds of that one, I gave up.

Any tips on what the problem might be besides the heatsinking.....   

Thanks, Daniel C

P.S I wonder if this has anything to do with the giant capacitors I used for the PSU. 2 x 10000uf. The amp takes a while to discharge the large caps and will only start again once they are discharged  (I use the on/off LED on the secondaries to montior this).  have you ever heard of this phenomenon?

[R.G.]

You know, Daniel, most of the people here are the same ones you asked over at DIYstompboxes. 

[bamera]

It was suggested I post here in my DYIstompboxes thread... I feel a little sneaky copying and pasting here though

[joecool85]

You know, Daniel, most of the people here are the same ones you asked over at DIYstompboxes. 

That's not totally true.  I myself don't even check diystompboxes more than once a month anymore.  And I'm the one that pointed him over here  :tu:

I haven't heard of the issue with only being able to turn the amp on after the caps have discharged.  What happens if you shut it off, then turn it right back on?  It just doesn't work?  Are the diodes/rectifier getting really hot when this shuts down?

[bamera]

Hey Joecool85,

I got it working, the transfomer ground wasn´t hooked up to the circuit... something that hadn´t brought me any problems with my TDA2050 (R.G gave an explaination as to why).

The thread at DYIstompboxes is interesting and might help other beginners if you decide to point them that way

Thanks for taking an interest,

Daniel C

[joecool85]

http://www.diystompboxes.com/smfforum/index.php?topic=62530.0;topicseen

This is the link bamera was refering to