Buffer

Having performed the investigations I wanted on the gain stage on which I was working, I then moved on to another part of the project. And the chaos from a couple of days ago was nothing compared to yesterday.

While I was preparing to begin assembly of the vacuum tube circuits for the Source Selector Unit, I was quickly going over the design and pulling components. And this is when I became aware of a little problem with the buffer circuit.

About a month ago I had an exchange with a reader talking about The Purpleheart Signal Meters and modifying the project to provide multiple inputs and some gain balancing. I’ve been giving this a lot of thought in the last couple of weeks because I have the same needs. So I think this is going to be my next major project.

There are a variety of sayings, axioms, proverbs, or quips which could apply to me this afternoon. A few which come to mind include:

“How wayward the decrees of fate are” - Vanitas Vanitatum - William Makepeace Thackeray

or this one:

“Pride goeth before destruction, and an haughty spirit before a fall” - Proverbs 16:18

or just the simple axiom:

“It ain’t over till it’s over” - Yogi Berra

In any event, it would seem that “Final Chapter” or no, I have one more post concerning the Color Preamp.

So I decided today that I really needed to close the book on the color preamp. This means that I couldn’t just prototype a new buffer and leave it at that. The preamp needed an end-to-end test in it’s final design configuration. So that’s what I did. The results were even better than before.

Lots of work has been going on the last couple of days working on an alternate buffer design for the 12AU7 “Color” preamp. As readers should know, I was not particularly pleased with the performance of the previous buffer circuit. It was bottoming out at too low a voltage. Now however, I have a simple change which yields much better results.