The scenario went like this: I used to run this amp with +-20v DC, and it seemed to work fine except for a little bit of clipping. Now, I changed my mind to make it work with bigger voltage!!! I've increased the voltage to +-50V DC. After powering the amp, a nice smell got out but it was working!!! Now I didn't cut the power to experiment what actually happens. Funny isn't it? Anyway, so, after playing the amp for around a minute things got out of control with a little burst!!
Therefore I've opened the amp and found that the supply decoupling caps got fired along with a few small transistors and one Output transistor from one channel only!!! My amp got 4 channels!!!
So, I took out the burned parts and replaced only the decoupling caps. Problem arised when I powered it after replacing the damaged parts. The divider resistors in the diagram (marked red) are getting hot and funny smell is coming again. Now, these resistors have been changed when I opened the amp because they got burned out too.
I've checked all the components connected to that divider network but failed to find any visual fault.
What can cause the resistors getting too hot?
I've just replaced the 220 Ohms resistors with 1.2k. Still it's getting hot!!!
I think 1.2k won't hurt according to the formula!!