Trafo for 15W with an LM1875

[polo16mi]

Can you post some draw of your circuit?  Cant figure out wich resistor/cap you are talking about...

[Rutger]

I allready know what went wrong. I measured with the preamp disconnected instead of connected. When I'm at home I'll measure it again, but I don't forsee any problems now.

[polo16mi]

maybe thats the problem. i dont know how is your circuit, but, as you mentionted, looks like you are making some voltage divisor, so if nothing conected to it, voltage is practically the same as your power supply.

[Rutger]

Yesterday I finished the amp and it's alive!!  
It's very quite, no noises, cracks or hisses. There was a little 50Hz hum but I guess that's because I didn't use a grounded wallsocket. The preamp is running on +/- 18V and is doing just fine. Guess that the lifetime of the chip is shortened by running on it's max. voltagerating, but I can change it quite easily if I need to.

Didn't really had the time to test out the amp because my daughter already was asleep (and my wife wanted to watch her favorite tv-show...) But first impressions are good. I build the preamp of a Marshall Lead 12 and it definitely has the Marshall flavour and especially with the high-input it rocks like crazy.
This evening i'll make some time to test it at volume and to hear what it is capable of. Very curious!