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previous: Matt W. Re: Electar 10 mod Question/PCB mod -- 8/24/2000 10:01 PM View Thread

New mods to the baby marshall mods (kinda long)

8/25/2000 1:07 PM
Doug H
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New mods to the baby marshall mods (kinda long)
For anyone doing the Bob Clear baby marshall mod:  
 
I've done this mod and it sounds pretty good, but it's still a little harsh and raspy when I overdrive the 1st preamp stage with a pedal. So I've come up with some, IMO, improvements to it. It's not complete yet, but I'm getting very close to where I want to be. This is what I've done so far, you might want to try them as well:  
 
R4: 220K (although I may change it back to 100K)  
C2: .022u  
R5: removed  
 
R6: install a jumper - Then solder a 470K directly to pin 7 of the 12ax7 socket(this is the tube grid of V1-B -the 2nd preamp stage). Solder the other end of the resistor to the lead you removed from the pin. This will roll off the highs a little more and smooth it out, in addition it won't attenuate as much as if you just sub it for R6 on the board.  
 
C5: Jumpered  
R9: 33K (Leave the rest of the tone stack alone-although I subbed C6 with a 470pf mica. The jury's still out as to whether that was an improvement...)  
 
Did Bob's EL34 mod.  
Did Bob's NFB tweak (R14: 22K, C11: .068u)  
Installed a Weber C8SS speaker.  
 
I'm not using zener diodes right now, I may try that again later. My experience was that they flattened out the freq response and sounded sterile. But I have not tried them with this mod yet.  
 
At this point I have removed C1, and R3 is 1.5K, but this is where I'm tweaking right now so this may change. In addition, C4 is .47u and R7 is 2.7K, but they may not be after this weekend.;-)  
 
Basically, I just tweaked Bob's mods by mainly moving the grid resistor, and less extensive mods to the tone stack.  
 
I still have 2 problems I'm solving: 1)Lows are still farting a little, especially wound E string. Removing C1 helped, and I'm going to try increasing R3 (or lower R4) as well to lower that stage gain somewhat. May have to mod the second stage cathode circuit as well, but I'm going to see what this will do for me first. 2) The amp is still just a pinch too dark, for my tastes. I will experiment with a treble bypass cap around the 470K grid resistor for that.  
 
Bottom line: With Bob's mods, I needed to use a pedal that generated some internal distortion. Then I set the pedal to clip lightly, and set the level to overdrive the amp lightly. This yielded a good smooth tone, but it was still dependent on the pedal for providing some clipping. Overdriving the tube alone sounded harsh. In general, the high end was just a little harsh, to me.  
 
With these mods I'm using a clean boost, a pedal I'm breadboarding with 2 parallel JFET stages that can be mixed and are voiced like the 'bright' & 'dark' channels of a plexi - all clean. The tone is amazing, I'm getting good chunky mids, better bass response, smoother highs and distortion. When I scoop the mids, the tone stack really scoops. It will sustain forever, and it can get really thick, compressed, round tone as well as a wide range of brighter clean/semi-clean tones. It's bringing dynamics out of this little speaker I have not heard before. If I end up adding another tube I think I will be closer to where I need to be with these mods.  
 
Bob did a great job and without his mods I probably wouldn't have bought this amp, so no offense to the work he did.;-) This is just my personal twist-as always, YMMV.  
 
Sorry I was so verbose, I'm just really stoked by the tone I was getting last night, and I'm running on 5hrs sleep and lotsa adrenaline.;-)  
 
Doug

 
Replies:
Bruce So I guess you like this amp then.<... -- 8/26/2000 3:37 AM