MXR distortion+ issues

[Frances Rhodes]

hi everyone.
i built my first IC circuit, an MXR distortion+ on which i added a mod (asymmetrical clipping) and once i wired everything up and housed it, no sound would come out when engaged, not even a really faint/dull sound, just nothing at all.
the bypass signal goes through, no problem.

here is the schematics i used which i drew myself using the eagle cadsoft 5.11 version from the original schematics i found.
i used this to draw my own veroboard layout.

i use a DC plug instead of a battery.
i used a dpdt switch for true bypass.
the 10k resistor on the original schematic is missing between the coupling tantalum cap and the diodes (i forgot to include it in my vero layout, but i thought it wouldn't be a problem, since it appears to make a voltage divider with the output pot)
the output volume pot is a 10k linear (i got confused with the A and B notations for lin/log, but that shouldn't be that much of a problem either... will be replaced by a 50k log pot as soon as i have one)
distortion pot is a 1M linear
all resistor are metal film, 1%
i used an electrolytic cap instead of a tantalum cap for voltage divider (as indicated on my schematics) and film caps instead of ceramic (except for the feedback cap, which value was too small)
the diodes i used are AA 118 germanium diodes (which appear to be the cross reference match for 1N 270s)
the IC is a UA 741 CN

my voltmeter says 9.3V across the DC plug
the voltages on the IC pins are:
pin 1: 0V (not connected)
pin 2: 0.1V
pin 3: less than 0.1V (the pointer on my voltmeter hardly even moves, but still a little)
pin 4: 0V (grounded)
pin 5: 0V (not connected)
pin 6: 4.6V
pin 7: 9.3V
pin 8: 0V (not connected)

DC in on the circuit board reads 9.3V
ground reads 0V

i connected all grounds to the input plug except the distortion pot ground which is connected to the volume pot ground (both pin 3)

if you want pictures of the guts and the circuit let me know, i'll upload some in a reply.
thanks

ps: i apologize for any mistake i may write, i'm french and my english is not perfect, even after spell-checking!

[MikeH]

This looks like a job for (Da-dada-daaaaa!) - the AUDIO PROBE!

My guess would be that your signal is either getting shorted to ground at some point, or that there is a bad joint or component that is not allowing signal through.  Doing a search here, or even on google will show you how to build an audio probe, which you can use to trace the signal path and find out where you're losing signal.

[Mark Hammer]

Pin 3 should be at half the supply voltage, and pin 6 should NOT be at 4.6v (half the supply voltage).

[Frances Rhodes]

@Mike
i was afraid i may have to use a probe...
i ordered some components to make myself one, i'll try that!

@Mark
yeah, that's what i thought (at least about pin 3) but i measured the voltage between the two 1M resistors (R2 and R3 on the schematics) and the voltage is also 0.1 ish volts. i checked the resistors, they are all the same ones so i don't understand how the voltage can drop like that only across 1 resistor only

edit: i'll try to draw the vero layout i have to post it here, there certainly are some mistakes i didn't notice

[Meanderthal]

 Did you check the bypass switch wiring? It's easy to wire a 3pdt sideways if you're not careful. Got me a couple times...

[Frances Rhodes]

yep, i double-checked!

here is how it's wired:

[Frances Rhodes]

and here are the vero layout i used.
i'll check once again tomorrow to be sure that's how my circuit board is set up, but that should be it.

all resistors are 1M except for those labelled otherwise. the ceramic and tantalum capacitors are mentioned above the circuit (my software is missing a few symbols)
there are 2 jumpers under the 741 IC and one at the right end, connecting the 1n capacitor to ground (parallel to the diodes)
also there is a spst toggle switch across 1 diode (as seen on the schematics above)

[Fender3D]

Whether you have 0.1V at R2/R3/C3 node, you likely have R3 and/or C3 shorted somehow.
unless your ic is faulty of course

PS
tantalums and electros are polarized, any symbol with 2 pins and a "+" will work (better if with a capacitor shape.... )

[Frances Rhodes]

let's say the IC is dead, how can i be sure of that? i don't have my breadboard yet, will come in my next order alone with the supplies to make my probe, so it's not easy to test anything right now!

and about the caps, i just mentioned it because before i made the distortion+ i read a great deal about it and several times they said "tantalum caps are terrible for audio, but if the schem says tantalum, you have to use one!"
and the debug topic says we have to tell every substitution... so, as a newbie, i followed the rules!

i'll try to clean the space between the tracks to see if i still have 0.1V at that node
thank you all for the advice

[Fender3D]

let's say the IC is dead, how can i be sure of that? i don't have my breadboard yet, will come in my next order alone with the supplies to make my probe, so it's not easy to test anything right now!

Then checking R3 and C3 is faster, if it doesn't work then it's the IC

and about the caps, i just mentioned it because before i made the distortion+ i read a great deal about it and several times they said "tantalum caps are terrible for audio, but if the schem says tantalum, you have to use one!"
and the debug topic says we have to tell every substitution... so, as a newbie, i followed the rules!

i'll try to clean the space between the tracks to see if i still have 0.1V at that node
thank you all for the advice

My refer to capacitors came after this  

the ceramic and tantalum capacitors are mentioned above the circuit (my software is missing a few symbols)

[Frances Rhodes]

oh yes ok, i see, sorry! english gets confusing at night
i meant my software isn't made to draw vero layouts, so i cannot choose any leg-spacing i want (or if i can, i don't know how to!!), that's why i used false symbols to draw.

i measured the voltages again after cleaning between the tracks to be sure there isn't any solder "bleed" shorting 2 of them, i still have 0.1V at that node and also at the pin 3 of the IC.
just to be sure, i checked a hundred times but, the stripe on a electrolytic capacitor indicates the negative lead, right? but in the case i soldered it backwards, capacitors block DC currents so it cannot the short we're looking for...

i'm colourblind so i cannot verify the resistors values, but i'm sure all supposed to be 1M have the same colour-stripes, i just an't figure what colour they are. so R1, R2 and R3 are the same value.

i could try to desolder the IC (i didn't use sockets... now i realizing how big a mistake it is) and measure the voltages again, would this be a good idea? or i could try to desolder just R1 to break the link to the IC.

thanks again for the help

[Fender3D]

no problem mate,
desoldering R3 AND C3 and checking them should be faster.
Watch out, ICs are temperature sensitive, if you overheat them, they may act strangely or burn out...

[Frances Rhodes]

ok, i'll try that. i don't have a good solder iron yet, so maybe i over-heated the IC when soldering it in the first place