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previous: Mook This question is in regard to the s... -- 9/17/1999 12:53 PM view thread

Re: Trainwrecked Expresso question

9/19/1999 3:38 PM
Gil Ayan
Re: Trainwrecked Expresso question
quote:
"This question is in regard to the schematic at Steve A's site.  
 
 
 
After the tone stack and vol controls, the signal goes to 1/2 of a 12ax7. After that it "dumps" a bunch of signal (through a 56K resistor) and goes into another 1/2 of a 12ax7. This stage has a cathode resistor of 10K (if I remember correctly).  
 
 
 
What does this stage do? "
 
 
 
 
For starters one would think it kills the gain, since the gain approaches Rp/Rc (p = plate, c = cathode). However, you will eventually get some distortion that way because you are starving the tube of some current.  
 
 
 
Many modern amps like Soldano, The Mesa Boogie Recto, Broove Tuves (all of which can be found at Steve Ahola's schematics page, BTW), use a larger that usual cathode resistor at some distortion stage.  
 
 
 
So, I "had" to try that a while ago and found that the distortion you get is "harsh," really... not what I would consider too musical. Of course, if you change the resot of the circuitry to accommodate that, that's one thing, but I am not sure why some companies are using that method. What probably happened is maybe Soldano started it and the others copied the approach...  
 
 
 
Easy enough to try, Mook. In a distortion stage, put a 50K pot and hear the difference the various settings will make.  
 
 
 
Gil