Mxr Distortion +

[unclej]

i've been building this effects box and have run into a problem..it doesn't work.

i'm 99% sure that the board and all of the components are ok. soldering is clean and not flowing over to where it shouldn't so i've got a couple of questions about this schematic. (no big surprise there, eh?)

i've eliminated the ac adaptor so follow the + line up and over to the right of where it drops down into the op amp. what does the wire connect to at the point where the arrow and the V+ sign is?

ok, regarding the potentiometers...if i'm reading this right the output pot has a wire going to the left lug, the right lug goes to ground and the center lug goes to the on/off switch. that one makes sense. but the distortion control pot looks like the wire coming from the 4.7k resistor goes to the left lug and the right lug goes to ground. but it also appears to me that the center lug goes to ground also. when i set it up that way the whole unit is dead. it's not working properly anyway but when i disconnect the center lug the guitar plays through in the off position and also in the on position but with a change in output strength.

so i'm hoping with those two bits of info this rascal will work. i'm fairly certain that everything else is ok.

[url=http://www.harpamps.com/schematics/mxrdistp.pdf]

edited to say: sorry about that..i thought that would come up as a link but it didn't . if you wouldn't mind the old copy/paste routine i'd appreciate it.

[Saber]

If you're referring to the clockwise lug as the left lug, then you're correct for both pots. But it doesn't make sense that connecting the middle lug to ground kills the sound, and it's not immediately obvious why.

And the arrow with the V+ at the top simply connects to the other arrow with the V+ at the bottom if you want the LED to light when the effect is turned on.

Edited December 20, 2004 by Saber

[lovekraft]

Here's a couple of layouts for that circuit - they may give you a better idea of what you've got hooked up wrong.

From General Guitar Gadgets

From Tonepad

Maybe that'll help - I always have trouble remembering the pinout on single opamps, so I wire 'em wrong about 1 out of 3 times.

[unclej]

well i guess i'll have to go back in and check that i've got all the components wired up properly. the op amp is the one thing that i'm sure i've got right. it's more likely that i did something wrong with the input or maybe the on/off switch.

i guess if it was easy it wouldn't be fun...yeah, right.

thanks to both of you.

edited to say: DOH! i take it back about being sure of the op amp. i reversed pos and neg. works a lot better now.

[lovekraft]

Been there, done that!!

Glad you got it working - now you can mod it into an OD-250 or a YJM308 if you want to.

[LukeR]

I dont know how, but I am willing to bet that the Zakk Wlyde overdrive is a modded Distortion+. (Well, I mean the same base circuit as the Dist+, OD-250 and th YJM).

I havent seen the schem for the Zakk myself, but I am sure it is around.

Just another (possible) option,

Luke

[lovekraft]

You'd lose - the ZW44 is basically a modded Boss SD-1, with clipping diodes in an opamp feedback loop, like a Tube Screamer.