Wednesday, May 8, 2013

Interesting Readings

I'm going to use this blog post to share some interesting information.

First, I've been looking at the Leach class handout and the Yamaha P2100 design.  In particular I've already said that I'm really pretty shocked that the amp sounds so good doing so many things we wouldn't do today.

From the Stereophile Carver Challenge - Page 4

I would like to quote:

On the face of it, what Bob Carver pulled off should be impossible. You can't make a silk purse from a sow's ear. What about the audible differences between transistors, capacitors, internal wiring—all the things that we know contribute to the superiority of no-holds barred amplifiers? What about all the things that amplifier designers have learned during the past 20 years, which enable them to build better amplifiers (at whatever price) than have ever been built before? How could all of these things have been factored into the relatively quick and painless transformation of an average amplifier into a world-beater? But, of course, the "factoring-in" was the key to all this.

This is kind of where I started with the Yammies.  WHY do they sound so good despite doing a number of things "wrong" compared to today?   And why do they spend money on an extra pair of transformer windings to provide extra negative voltage to the cascode differential pair on the inputs?

A very interesting read on circuit memory and the use of the cascode differential pair inputs:

http://peufeu.free.fr/audio/memory/

It's all starting to make sense.... just barely.

Yamaha Protection Circuitry

I spoke a little too soon about the Yamaha not having any protection circuitry.  Looking through my class handouts/notes from Dr. Leach's lectures, TR12 and TR13 provide current limiting.  If either saturates they remove voltage from the base of the drivers, TR14 and TR15.

I stand by my original assessment that the temperature light is a waste of good power best used elsewhere though.

I'm still trying to figure out the extra windings which are used to add about 14V of negative supply, which seems related to the bias and input stages.   It's almost as if they are trying to keep the input off center, so it operates linearly, before driving the rest of the amplifier in a more balanced manner.

Ideas?