K8060 200W distortion problem

I have just recently assembled three of the K8060 200W discrete amplifiers. I have connected them to a 4 ohm load.
They sound OK at a moderate level but when I try to turn them up there is extremely bad distortion, not like usual distortion that you get when just pushing a amp to far, more of a popping on the base.
I also have a cheap commercial 200W amp made by Skytec. This on paper would appear to have a lower Spec but sounds great at a much higher volume.
I am using your HSVM100 Heatsinks and 0-30 0-30 120VA Toroidal Transformer. I have also tried changing the 3300uf capacitors for 4700uf with no difference. I have set the BIAS 10 exactly 10mv. At the Power diodes I have about 45V and at the zenerdoide I have 9V.
I would appreciate it if you could point me in the right direction.


Please check if there is no ground loop problem.
aslo check if the preamplifier is not the source of the distortion.
If the pre amp can not deliver the needed output level, then this one can introduce the distortion.

Hi, did you solve the distortion problem?