James Perrett wrote:ef37a wrote:Hah! I spent a nifty on a book and although Current Dumping was only a small part of the many things I hoped to learn, there was next to naff all about it!
That's probably down to Doug Self not rating it as a useful design. John Linsley Hood has a few paragraphs on it in his "Valve and Transistor Audio Amplifiers" book but there are also plenty of web resources covering the 405 and its successors.
PS - Amazon is listing a copy of the Linsley Hood book for under a tenner from one of their alternative suppliers at the moment.
Thanks for that James, daughter can treat her old dad for that Dad's Day!
There is another amp design D S seemed a bit cold one? The "Edwin" amp. There you had the OP Transistors "just" not conducting and the speaker was driven at very low levels by the driver transistors*. As the drive current increase the voltage across the 100Rs in the power trans base circuits increase and caused them to start to conduct. All under feedback control. The design could not achieve distortion levels in 4 decimal places as do the best of Self's offerings but I am not sure we need such low figures, not for any but THE most esoteric purposes anyway?
*The Sinclcair Z50 was an Edwin op stage and was pretty good even if "50 watts" WAS rather optimistic! I actually built two "rips" using what I had available, TIP41/42 iirc and used them in bridge mode to drive a 10 foot column speaker. That system chucked it out I can tell thee! Sounded a hell of a lot better than the 15" disco "bins" you saw in the day, at least for vocal signals.