Print Page - MXR Distortion+ Problem

Title: MXR Distortion+ Problem
Post by: Hydesg on July 07, 2004, 10:25:31 AM

hi guys
im facing a big problem now
just completed soldering the schem on a perfboard
problem is that it doesnt produces any output

checked the voltage at the ic chip

it shows

1)0
2)0
3)2.9
4)0

5)0
6)8.8
7)8.8
8)0

any idea where is the problem?

ive checked for short circuit
but there seem to be none

i omitted the 10pf
and used a lin1M pot

used all ceramic caps
and a ua741cn chip
please help me
thank you

Title: MXR Distortion+ Problem
Post by: jimmy on July 07, 2004, 10:34:53 AM

hmmmm

check pins 2 and 6, they look pretty off...

http://www.generalguitargadgets.com/v2/diagrams/dist_ic.gif

have a look at that if you need more help

good luck
Jim

Title: MXR Distortion+ Problem
Post by: Hydesg on July 07, 2004, 10:47:23 AM

ive seen the page

the voltages are off
but i dont know what went wrong?

Title: MXR Distortion+ Problem
Post by: jimmy on July 07, 2004, 11:14:54 AM

build an audio probe. that should narrow it down a fair bit.

good luck
Jim

Title: MXR Distortion+ Problem
Post by: Hydesg on July 07, 2004, 11:23:18 AM

hi
the
there should be 4.5v in between the 2 , 1m resis
as its a voltage divder i guess?

i treat probing
theres only 2.95v
could tht be the prob?

Title: MXR Distortion+ Problem
Post by: jimmy on July 07, 2004, 11:34:10 AM

yes yes i imagine that is the problem.

is your battery flat? if not check the connections:
v+ to the 1M, then the other two 1Ms come off that, one to ground, one to pin 3.

good luck
Jim

Title: MXR Distortion+ Problem
Post by: Fret Wire on July 07, 2004, 01:34:10 PM

Since you used all ceramic caps, your only orientation worries are that the diodes, and op amp are orientated correctly. Double check your resistor & cap values, always a good idea to use a DMM to check every component before you install it. Check your soldering again with a magnifying glass to make sure none of the non-connected solder pads have been accidently bridged. Check your off board wiring also. Did you perf this one also?

Title: .
Post by: petemoore on July 07, 2004, 01:52:30 PM

I use my thumb as an input source, then work from the output side toward input, to find where the signal is getting lost, but you should get the voltages close on the OA before you try that, it's possible that's the only problem in this case.
I also just go from Pin 1 & 2, [after removing the OA] and check for continuity with the DMM, if it beeps, there's a problem with the IC socket wiring. Then pins 3&4, 5&6, etc. checking all the IC pins for shorts, as the pin/pad soldering under the board can get tight.

Title: MXR Distortion+ Problem
Post by: Hydesg on July 07, 2004, 09:46:23 PM

seems like 3v comes out from the 1M resistors

could that be a problem?

meansured 1uF+ side i got 3v
the 3 1Ms got 3v
and the one connected to batt has got 9v

Title: MXR Distortion+ Problem
Post by: Fret Wire on July 07, 2004, 10:40:25 PM

What schematic are you going off? Did the schematic use a single or dual op amp? Did you double check your soldering around the IC?

Title: MXR Distortion+ Problem
Post by: Hydesg on July 07, 2004, 11:14:38 PM

im using the distortion+ schematic at general guitar gadgets

ive checked for short circuit in the ic

its a single op amp design

could it be the chip or anything?

ua741cn

i rewired another 4.5V bias circuit inside(which made it look messy)
and its still the same
checked all connections and they were right
i wonder what went wrong inside

Title: .
Post by: petemoore on July 08, 2004, 09:47:50 AM

Sure it could be the chip, %ages aside...worth a check.
Are you getting ~1/2 v at the divider?

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DIY Stompboxes => Building your own stompbox => Topic started by: Hydesg on July 07, 2004, 10:25:31 AM