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Posted by Poindexter (M) on October 26, 2006 at 19:32:10

In Reply to: Magic Boxing Poindexter's Musical Machine posted by uW on October 23, 2006 at 19:19:50:

First I would reassure you that you have not insulted or offended me.  Maybe twenty or thirty guys have built the Machine, that I know about, and not one of them has built what's on the page.  In fact the only 'straight' build I know about is a European gent who built a Mœbius right from the parts list, complete with a very nice job on the divided chassis.  You are perfectly welcome to any and all the info in that project, to use as you wish, or not.

I think that maybe I did not make my point well; that if you are trying to improve the Machine musically, lobbing power supply and bias circuit elements at it sort of randomly to see if any of them stick is going to have a pretty low chance of success.  Not because it's the Greatest Design Ever, or because I have such awesome academic credentials (thank you, gusser), but because it is a simple circuit that has been very thoroughly developed.  I am myself constantly working on it still, and I can tell you that I'm down to about one success in four very carefully thought-out tries.

I now see from your later explanation that you do have a plan, involving the 'magic box' technique (which I didn't know about, I'll have to have a look). I do hope you'll report back on what you find.  I do myself think a CCS for the front end diff-amp a very good idea.  This seems to be a subcircuit that has very little sonic impact in my experience, and I'm now looking into front-end tubes that are vastly superior in chars, but require almost twice the current to 'get on the cam', so my sharp-stick solution of a largish voltage negative supply and high resistance would use too much power and generate too much heat inside the chassis to be practical.  Russel is right that if you use a CCS here, there's no need for the differential in the load resistors for the stage, which is compensation for the noninfinite signal resistance of the tail.

Please keep me advised how your project is going, if you have time, and I'll go over and look at the magic box.

Aloha,

Poinz

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