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MXR Distortion+


 
10/27/1999 10:29 AM
JD Sleep
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MXR Distortion+
I almost don't want to post anything about this pedal, since most folks in the last thread on this subject thought its tone sucks...here goes anyway.  
 
I wanted to mention that the cheapo 741 opamp may have something to do with GOOD TONE in this unit. I think my home-made Dist+ sounds great. It's not to bright, trebley, or screechy as described by some. I have a 6 position switch for different types of diodes, including a position for diode bypass. Guess what, even the diode bypass position distorts! It's not a real pretty distortion, but it's not real ugly either. Is it due to the cheapo chip? Maybe I just accidently built the one unit that sounds good? (I built it on perfboard to the exact specs of the schem) I HAVE heard other people say they like the Dist+. I'll try some other opamps and see if it makes any difference.  
 
JD  
PS - My favorite setting is with Red LEDs.
 
10/27/1999 12:00 PM
Tobias Karlsson
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quote:
"I wanted to mention that the cheapo 741 opamp may have something to do with GOOD TONE in this unit. "
 
 
I've heard the same thing from a guy here in my hometown. He says that the sound isn't so harsh with the 741 chip compered with a TL071 etc.I haven't tried it myself though.  
quote:
"Guess what, even the diode bypass position distorts! It's not a real pretty distortion, but it's not real ugly either."
 
 
I have also noticed this with some other diode clipper designs!  
Im wondering if the main part of the distortion sometimes is from the OP-amp and the diodes just compress and smoothes out the sound a little bit?  
 
 
Tobias Karlsson in Sweden  
 
10/27/1999 12:36 PM
A.S
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I tried a DOD 250 once. Its designed pretty much the same as the MXR but the 250 sounded much, much better.  
Ive never cared too much for the Distorsion+, I like my  
-77 Boss OD-1 better for that kind of sound.  
 
A.S (also from Sweden)
 
10/28/1999 10:27 AM
Dai Hirokawa
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Hi JD, I built one also (out of the schematic plus pic of the innards in a mag), and I too think there is more to this unit than previous postings suggest. Mine was built around a 741, some carbon comps(the two 10ks and 4.7k), carbon film(the 1Ms), Ge diodes, ceramics, and less harsh sounding tants w/what sounded like poorer high freq. response. I also "massaged" it some slightly different values(2.2uF to 4.7uF for the coupling cap, 1500pF to 2200pF at the output). It's a pretty simple circuit, so the sonics of the parts used should affect it a lot, I'd think.  
 
>>Guess what, even the diode bypass position distorts!  
 
I would think that removing clipping diodes would make it louder but less sonically dynamic(I usually favor keeping the diodes when they are clippers).  
 
Anyway, JD, you're not alone...  
 
Happy tweaking!  
 
Dai Hirokawa
 
10/28/1999 1:10 PM
JD Sleep
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Dai,  
 
>>I would think that removing clipping diodes would make it louder but less sonically dynamic(I usually favor keeping the diodes when they are clippers).  
 
I wired a diode bypass thinking it might make a good booster with no clippers...I was wrong. Next time I open it up, I'm adding another diode variation to replace the bypass switch setting ;>)  
 
Thanks for your input, I might try some of your tweaks if I get a chance.  
 
JD
 
10/28/1999 1:38 PM
GFR
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The 741 has several flaws. It has poor frequency response, very limited slew rate, and has a class B output stage that will add lots of crossover distortion. It is also noisy and has a low input impedance when compared to a Fet input opamp. It also has a limited output current capabillity that can distort when feeding a low impedance load (like a diode conducting?). I don't think anyone can find the noise and crossover distortion good no matter how subjective tone is. Slew rate distortion is also normally agreed to sound bad. The frequency response limit can be a good thing in a distortion pedal but you can do it by adding a small cap on the feedback loop of a better opamp. Maybe the output current limit into the diode clippers may affect the sound in a good way (but I doubt it).
 
10/28/1999 3:30 PM
JD Sleep
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GFR,  
 
>>Maybe the output current limit into the diode clippers may affect the sound in a good way (but I doubt it).  
 
You won't get any arguments from me about the lousy spec of the 741 IC. However I do think there is something about the IC that "works" with the design of THIS effect. The 741 IC may be the best choice in THIS design. Substituting an IC with better specs may make a somewhat workable sounding effect completely horrible. This is really the question that induced me to start this thread. I guess your point may be that the design of THIS effect is as lousy as the IC it uses!  
 
>>I don't think anyone can find the noise and crossover distortion good no matter how subjective tone is.  
 
The noise level of this unit may be realitively high compared to a FET input opamp, however it is VERY low compared to my "descrete component" Fuzz Face. The Dist+ doesn't have a loud buzz or hum during silent on-time, like a Fuzz Face does, yet the Fuzz Face is very popular and workable for some guitar players. This Dist+ sounds good to my ears using my guitar and amp setup despite the crossover distortion.  
 
Would you make somewhat similar comments about the Fuzz Face since the specs on germanium transistors are so much worse than modern transistors?  
 
JD
 
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