driver caps 100 watt PA

[rtill]

curious about http://sound.westhost.com/project3a.htm
the driver caps are 100 pf on the bd140 transistors
what do these caps do? If I change them to a higher value (470 pf), will I get a duller sound?
I read on one of these forums that a higher value will "suck the life" out of the transistors....I don't know what that means.....

Thanks!

[nigelwright7557]

The first one is a miller capacitor.
It basically slows down the slew rate so you dont get oscilation.

An amplifier is similar to a servo system and a servo system requires just the right amount of gain. Too little and the output is sluggish, too much gain and you get oscilation.

If you increase the capacitors you will lose some high frequencies.

If you decrease the capacitor you could get oscilation.