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MXR Distortion + bass mod, HELP HELP!

10/25/1999 10:34 PM
MXR Distortion + bass mod, HELP HELP!
Ok, I'm completely new and green to all of this, so please talk to me in lamen's terms here. I know the basics of electronics but apparently I need to study up more. :)  
I would like to increase the bass response on my MXR +. A site read that all I need to do is increase a capacitor along the output to like .1uF. Ok....  
When I opened it up, the only capacitors I can find are these:  
2 small yellow ones reading: "105 +35k"  
one big round one reading: "16V 100 uF"  
and 2 red ones reading "2A 473J"  
Please tell me in lamen's terms which capacitor I need to change to do this mod? Thanks a million to anyone who responds!  
10/25/1999 11:01 PM
473 means 47 times 10 to the 3 picofarads  
= 47000 pF = 0.047 uF  
105 means 10 times 10 to the 5 pF  
= 1000000 pF  
= 1 uF  
So there doesn't appear to be a 0.1 uF.
10/26/1999 2:44 AM

"473 means 47 times 10 to the 3 picofarads  
= 47000 pF = 0.047 uF"
Wow Peter, I've never heard anyone describe it like that!  
Tickled me.  
10/26/1999 3:11 PM
Mark Hammer
There are two aspects to "increasing the bass response". One is to simply permit more low end to come through via changing the low end rolloff at different points in the signal path, and you have correctly identified this as an issue of changing capacitor values. The other way is to change the relative balance of higher and lower frequency components of the resulting output.  
In the case of some distortion units, such as the Tube Screamer, there is deliberate low-end reduction up front to alter the way the unit distorts. In the case of the Dist+, there doesn't seem to be anything in the design that deliberately restricts low end too much, although the first cap that the signal hits could probably be upped from .01uf to .033 or .047, and the cap on the output of the op-amp could be raised from 1uf to 2.2uf or 3.3uf (making sure to observe proper polarity) to let a little more bass through.  
The other thing is that you could consider adding a second pair of diodes in series with the existing ones to provide a higher clipping threshold. Bear in mind that the relative balance of high and low end is partly determined by the compression introduced by clipping (i.e., if my bass notes can't be any higher amplitude than my treble notes, then they will sound about the same loudness).  
Finally, you can alter the relative balance (i.e., make it sound like there is more bass by getting rid of the treble) by tacking on a treble-cutting capacitor on the output. This is probably the simplest mod because there is nothing to take off the board itself, and the insertion point is easy to identify. Simply solder a capacitor between .001 and .01uf to the outside lugs of the volume control, and away you go.
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