battradio wrote:Just make sure the DC offset is less than .1 volts , also check the cap at the bottom of the feed back loop is good , if its week or bad i can cause a turn on thump .
Make sure that the + & - power supplies come up at the same time and equal , bad power supply caps can also cause the thump .
Won't a bad feedback cap to ground contribute to a high DC offset ? Also, won't that high a DC offset cause additional possible problems at a higher output level? When working on SS amplifiers I won't run them for very long unless I can maintain a DC offset lower than 100mv and try to get this down to less than 30mv or lower before I send them out the door. As a course of normal repair I generally just replace the feedback cap to ground if the amp has any age at all. If DC offset higher than normal results I match up another set of transistors for the diff input and in the case of the Ampzilla/SAE group a matching of the quad diff transistors is in order.
Yes, you are correct in that the power supply caps, the feedback cap, and sub power supplies like + and - 15 volt supply caps for opamp front ends also need replaced.
Another thought.... sometimes resistors need to be added to the power supply caps to aid in both the power up and power down to maintain a nice even charge and discharge of the power supply.