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Marshall master volume preamp


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3/31/1998 5:45 PM
R L
Marshall master volume preamp
On the schematics section of this site there is a schematic for a Marshall master volume preamp that uses a clever jack wiring system to select an additional triode stage. Does anyone have any experience with this circuit? Does it sound good?  
 
Thanks for any help,  
RL
 
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3/31/1998 6:46 PM
TMiller

That is the preamp that Marshall used in the models 2203 and 2204 which were made from 1975-1989. It sounds great if your into that high gain preamp type of sound. I prefer the preamp in the model 1987 or 1959 though. Plugging into the second input gives a clean sound that is usable, but not great. You can't get a clean sound out of the first input, unless you remove the .001uf cap that goes across the volume control, but then your high gain sounds will be kind of muddy at settings between 6-9.
 
3/31/1998 11:28 PM
Steve A.

TMiller:  
 
You can't get a clean sound out of the first input, unless you remove the .001uf cap that goes across the volume control, but then your high gain sounds will be kind of muddy at settings between 6-9.  
 
    Sounds like it'd be a good idea to put the .001uf cap on a center-off DPDT mini-toggle switch to let you choose between .001uf, 0uf and something between 50 pf and 250pf, (maybe with a 1000pf mica cap instead of the .001uf cap). Thanks for the input on this.  
 
Steve Ahola
 
4/1/1998 2:32 PM
TMiller

A 500 pf cap sounds pretty good there. .001 uf and 1000 pf are the same value.
 
4/2/1998 1:01 AM
Steve A.

TMiller:  
 
.001 uf and 1000 pf are the same value.  
 
    I guess I should have spelled MICA in caps for emphasis... While the values are the same, the composition and tone of mica caps are quite different from other types of caps. (All of the mica caps I've seen listed are rated in picofarads- even up to 10,000pf!)  
 
Steve Ahola
 
4/8/1998 11:28 PM
Jim

>>>  
    I guess I should have spelled MICA in  
caps for emphasis... While the values are the  
same, the composition and tone of mica caps  
are quite different from other types of caps.  
(All of the mica caps I've seen listed are  
rated in picofarads- even up to 10,000pf!)  
>>>  
 
Steve, how is the tone  
different?  
 
Thanks,  
Jim  
 
 
PS - can somebody direct me to  
instruction on how to include  
quoted text in itallics like  
Steve did? Thanks.
 
4/13/1998 1:55 AM
Steve A.

Jim:  
 
PS - can somebody direct me to instruction on how to include  
quoted text in itallics like Steve did?
 
 
    I posted the HTML tags on the Announcement/Misc forum, but here it is again (with square brackets instead of angle brackets):  
 
[I][FONT COLOR=#0000AF"]quoted text[/FONT][/I]  
 
Steve, how is the tone different?  
 
    There have been quite a few threads here on mica caps- enter the keyword "mica" to see what hasn't scrolled off the Guitar Amps- General and DIY forums yet.  
 
    From an electronics viewpoint, mica caps are a lot more stable than ceramic caps throughout a wider range of temperatures so they are used in sensitive circuits like radios, etc. In guitar amps, they sound different to my ears. Ceramics may be a bit crisper, but mica caps give a very strong and clear treble sound. It sounds to me like they roll off the high frequencies above maybe 12khz a bit. I'm very pleased with them in Fender amps, but haven't tried them in a Marshall so I was wondering what the consensus was. (I know one "postee" had tried the mica caps in a Marshall and went back to the ceramic caps. I think I would have tried a few other values before giving up on them altogether...)  
 
Steve Ahola
 

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