ampage
Tube Amps / Music Electronics
For current discussions, please visit Music Electronics Forum. New: view Recent Searches.
New: visit Schematic Hell!
The sunn still shines online!

 
Listen to great tunes streaming live right now!

ampage archive

Vintage threads from the first ten years

Search for:  Mode:  
previous: ryan hi. i have a marshall 800 (4210) th... -- 1/6/1998 12:02 PM View Thread

Re: adding diode clipping

1/6/1998 12:30 PM
R.G.Re: adding diode clipping
I don't keep amp schematics here, but if it's the Marshall schematic I was thinking of, you may not be getting diode clipping at all.  
 
One of the Marshalls has four diodes in series/parallel in the preamp path. I thought that they were there for clipping myself for a long time. I was in the middle of typing a tirade about grid blocking, the "farty" sound of overdriving a triode into positive grid voltages, when it struck me that if you have diodes that clamp the grid overdrive to a succeeding tube stage so it is not overdriven so much, but instead is only just barely into distortion when the diodes conduct and keep it from going any further, you keep grid blocking from happening and at the same time can use very high gains without huge signal levels.  
 
I think that is what is happening in the Marshall.  
 
For more distortion out of what is there, just short out one pair of them, leaving only one pair  
in paralell to ground. That will cut the clipping voltage in half to 0.7V from the 1.4 is is now.  
 
You may hear diode clipping for the first time that way. I don't know any way to select something that adds distortion but is transparent to tone (whatever you're using "tone" to mean).  
 
Diodes in parallel do not add. Only the lowest forward voltage diode conducts, and the others never do conduct. Diodes in series add a forward drop to the clipping voltage with each diode, and it comes in discrete chunks, 0.7V, 1.4V, 2.1V, etc.

 
Replies:
ryan hi R.G. thanks for the reply. i sa... -- 1/6/1998 1:47 PM
Doc R.G.,I vaguely remember one... -- 1/6/1998 2:39 PM