need help with opamp big muff pi!

[cooldude666]

Hi, i'm trying to breadboard out an opamp big muff from gaussmarkov's schematic, but im hitting a wall. for some reason I can't deduce I'm not getting sound output from the 2nd IC. I've ran my signal tester everywhere up to there and a nice clear sound comes through- but after that IC, nadda. Ive checked my connections, so i don't think it's a "lead in the wrong hole" issue. anyone have an idea of what i should be seeing for voltages here? my DMM on AC definitely shows a rise and fall on pin 6 (output) when i strum, but like I said- no sound from the guitar. banging my head on the desk here! thank you kindly for any and all help.

Here's what I'm getting at each IC pin, and at the diodes
IC1A
pin 1: 4.50 vdc
pin 2: 4.50 vdc
pin 3: 4.45 vdc
pin 4: 0.7 mvdc

IC1B
pin 5: 4.47 vdc
pin 6: 4.50 vdc
pin 7: 4.49 vdc
pin 8: 9.01 vdc

IC2
pin 1: 7.10 vdc
pin 2: 7.91 vdc
pin 3: 6.55 vdc
pin 4: 7.11 vdc
pin 5: 7.11 vdc
pin 6: 8.30 vdc
pin 7: 9.00 vdc
pin 8: 0.00 vdc

D1
A: 7.90 vdc
K: 7.64 vdc

D2
A: 7.64 vdc
K: 7.37 vdc

D3
A: 7.37 vdc
K: 8.30 vdc

D4
K: 7.98 vdc
A: 7.74 vdc

D5
K: 7.74 vdc
A: 8.04 vdc

D6
K: 8.04 vdc
A: 8.30 vdc

[Govmnt_Lacky]

IC2 shorted Pins 4 & 5  

Pin 4 should read 0V

-OR-

Is IC2 backwards??

[cooldude666]

i'm about 99% sure it's not backwards, unless they notched it wrong?? can that happen? i suppose anything is possible. i tried swapping in another 741, and have the same problem so i /really/ don't think that's it. wish it were though..

i thought it was weird to be seeing that voltage on pin 4, but i'm not reading continuity between pins 4 and 5 so i don't think their shorted. could they be shorted internally and still not read continuity? im reading 1.2kohm resistance between them.

there's no connection leading to pin 5, and the only thing pin 4 goes to is the ground connection. where could that voltage be coming from??

[Govmnt_Lacky]

The fact that you are seeing about 0V on Pin 4 of IC1 tells me that there IS a good ground on the board. You need to trace back from Pin 4 of IC2 and keep going until you see either a break OR a connection to some form of V+.

With power off, use your DMM to read continuity between your circuit's input ground and Pin 4 of IC2. If it is not directly shorted, there is a problem somewhere between the circuit ground input and Pin 4 of IC2

[cooldude666]

huzzah!
there actually wasn't a path to ground. for some reason my breadboard's + and - rails are split into 2 segments rather than just being continuous.  i jumpered them together and NOW it works great. wonder why they decided to do it this way. seems dumb.

[R O Tiree]

Most breadboards I've come across have the rails split this way. I suspect it's so you can have more than one pair of supply voltages (+9/-9 and +5/-5, for example) and GNDs on the same unit.