Those Inter-stage Coupling Caps

[uneumann]

Fortunately, it is discussed at some length in my book
[ATTACH=CONFIG]32679[/ATTACH]

Yes - of course the topic is mentioned in scattered places. Credit goes to your treatment for the PI-output stage and general discussion. There are also some golden comments scattered in this thread already. There must be dozens of time-varying phenomena people have noted in tube amps. I agree most have probably been found and described somewhere at some point.

I'm game to collect these observations and create a reference of what they are, how they operate, and perhaps even how to create more of them or minimize those (like blocking) that are problems. I ask anyone interested in this topic to contribute a short description of their favorites. Send them to me and I'll compile them with attribution. There are examples of such "crowd sourced" references in other fields. My native field (what they pay me for) is computer graphics and there are a series of books called "Graphics Gems" that were created over the past decade by people submitting short pieces on good ideas and methods. Why not for this topic? Send me your thoughts, observations, and ideas related to non-linear or time-varying behavior of amp circuits and I'll start compiling and organizing them. I'll find a public place to post the collection from time to time so the whole community can access it.

uneumann@gmail.com

[teemuk]

Then of course, at some point, we simply get diminishing returns. Take aforementioned Carvin for example: Murphy's idea about interstage DC level shifts vs. symmetry/asymmetry practically culminated to the "Quad-X" preamp. The idea of the high gain channel was basically to cascade as many gain stages as possible within limits of stable operation, and tweak each stage for preferred amount of overdrive and overall symmetry/asymmetry. Now instead of usual two to four cascaded gain stages the high gain channel feature eleven! But seriously, how many of us can really tell a difference to other high gain amps with less gain stages? Apparently we do need some interaction for dynamic sound, but beyond certain point it really doesn't matter that much.

In an interview Murphy himself mentioned that pre and post equalizations are "absolutely critical adjustments". Strong statement, for good reason. There's a pitfall in limiting yourself to look only how things overdrive. Good tone is a sum of many different characteristics.

[tedmich]

Teemuk's mentioned paper