209.97.232.111
In Reply to: RE: (Tube) circuit topology posted by Jim Austin on May 15, 2009 at 11:37:55
Hi Jim,
You are headed down a treacherous path.
The problems are two-fold. First and most important, there is not necessarily a strong link between circuit topology and sound quality. In tube amps especially, I would say that the power supply has *at least* as much influence on the sound as the actual circuit or even the parts quality.
For an example of this, try and dig up some information of the "Paoli mod" for the ARC SP-3a. The original preamp had an emitter follower (capacitance multiplier) to regulate the main rail. It was a zero-feedback design. Then a company out of Paoli, Pennsylvania offered a complete PCB that replaced the original regulator. It was a high-feedback design using a floating 3-pin regulator. The bass got *way* tighter and there was a lot more definition. (Remember, the slogan on the front panel is "High Definition".)
But after living with the thing for a month or two, out it came. Too fatiguing and non-musical.
The second problem is that there are simply too many variations to make a simple taxonomy that will cover them. But there are a couple of things you can do. One is go to a good research library and find the MIT series on tube designs written during the war. I believe Hillman was the principle author of the compilation and it featured the first known example of what came to be known as a "cascode" configuration. This was re-discovered in the '80s and used by a great many companies that are now out of business. It's even used by a few companies that are still in business.
The other thing you can do is download a bunch of the Audio Research schematics. There is an un-official website that has info on almost all of their products, including schematics of a great number of them. They were instrumental in bringing balanced circuitry to tube audio, and all of their power amps have always featured a thing that is sometimes called "partially cathode coupled", but in reality is just a local feedback loop around the output stage (as is the so-called "ultralinear" configuration).
Also, visit Allen Wright's, Vacuum State Electronics websites for some nice modern schematics.
Have fun, but don't expect to get anywhere close to where you thought you were going...
Follow Ups:
Post a Followup:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2009, Audio Asylum, all rights reserved ]
[ Go Green ]
[ Take5 ]