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previous: Al Re: Marshall Tone -- 12/6/1998 11:33 AM View Thread

Re: Marshall Tone -- HOLD EVERYTHING

12/7/1998 5:51 AM
Mook
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Re: Marshall Tone -- HOLD EVERYTHING
I opened up my re-issue 50W plexi to change the stock caps to Orange Drops a few days ago. Yesterday, I did so checking of the circuit board, just to make sure things are up to snuff.  
 
Well...they weren't. I found two major snafus that are not on the available schematics.  
 
The first problem was the presense control. It was wired totally different than the schematic. In addition the feedback resistor was a 100K instead of the usual 47K.  
 
The second problem was the coupling caps. On the schem, there are coupling caps coming from each side of the PI and goes into the grid of the EL34. Both caps are rated at .022uF. In my amp, one side had the .022uF and the other side had a .1uF.  
 
Well to fix things, I put both PI coupling caps to .022 Orange Drops, replaced the feedback resistor from a 100K to a 47K, and changed the wiring on the presense contol to that shown in the schematics.  
 
After plugging in, I amp was totally different. It did not distort near as much as before, In fact it remained rather clean. Also, it had alot more harmonics and retained the guitars character alot more.  
 
My Marshall distortion was gone and I was crushed.  
 
Seems changing to Orange Drops increased the harmonic content. But decreasing the feedback resistor seemed to decrease the distortion factor. Can I disconnect the negitive feedback in the Marshall? I realize the Presence control will not work after that. Should I changed both PI coupling caps to .1uF (remember, one was .022 and the other was .1uF)?  
 
 
Dazed and Confused,  
Mook

 
Replies:
Richie Mook; I use the .1uf caps in mine t... -- 12/7/1998 6:36 AM
Mook What would happen if I added a .68u... -- 12/7/1998 8:58 AM
Bruce HI Mook!Hey, Are you sure you ... -- 12/7/1998 12:01 PM