pioneer A400 speaker pop

[glennjarrett]

i have a pioneer A400 which has developed a problem when you switch amp off sometimes the speakers pop as though the relay is slow and not switching the speakers off before the amp powers down, it takes about 5 seconds for the relay to kick in from switching on the amp . i have measured the voltage at speaker posts with no speakers connected and at switch on reads 50mv dropping to 3 to 5 mv on each channel ? .

[sakis]

there might be something wrong with the sequence of shuting down the relay quickly
on the other hand it could be as well a capacitor issue ..

To be more specific since i cannot analyze the protection circuit for you , any capacitor that is leacky might provide less or improper voltage resulting that amplifier goes out of balance during shut down . ( in such a design that stays in balance till complete shut down the protectin sequence is not that importand )

one could look at the protection circuit but also a good inspection on the capacitors especially in the protection psu and auxiliary psu

schematic is available if you like to have it just e mail me

kind regards
sakis

[glennjarrett]

hi thanks for the advise sakis i have found it was the bias set too high, it was set at 60mv per channel.
60mv divided by the resistor 0.33k = 181ma . i have set it to 20 mv and the problem has gone . will try to get it up to about 50mv which is 151ma as the higer bias current gives a better sound stage .

[sakis]

i am not really sure that you are in the correct track ....