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Re: Dumble


 :
7/4/1999 12:01 PM
Steve A.
Re: Dumble
bw:  
 
 
 
    Since the ODS is based on a BF circuit I suspect that the driver is supposed to be a 12AT7 (but then again some people replace the drivers on their BF's with a 12AX7 for the extra gain and distortion).  
 
 
 
Steve Ahola
 
7/2/1999 8:20 PM
Mook
"Jazz" switch
What does the "Jazz" switch do?  
 
 
 
Seems like it drops the bass and raises the (upper) mids.  
 
 
 
Is that right?  
 
 
 
Mook
 
7/4/1999 0:39 AM
Mook

This question is in reference to the 50W #49 Dumble OverDrive Special listed at Steve Ahola's site.  
 
 
 
While I'm at it, what function do the 500pF caps (Going from plate to cathode) provide in the OD section of the amp?? Seems like they "bleed" off higher frequencies in order for the circuit to "focus" on the mids.  
 
 
 
Mook
 
7/4/1999 9:20 PM
Gil Ayan

Hey Mook,  
 
 
 
1. The Jazz switch will take away some gain and emphasize the lows.  
 
 
 
2. The 500pF caps from plate to cathode on the OD stages are there to take some of the "Zs"out of the distortion, but it won't be as radical as saying bypassing the 100K plate load resisotrs with the same 500p caps (Soldanos and Mesa Rectos bypass the plates with .001u). I think it will make the overdrive stages more stable though, keeping potential parasitic oscillations at higehr frequencies under control.  
 
 
 
Gil  
 
 

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