TS Son of Screamer build issue ?

[HOTTUBES]

I built another SOS vero build , i have it all boxed up , but the drive pot does nothing , every thing else works fine .
I have checked all the board layout to make sure it's correct first off ...
All components were checked with a DMM before installation on the board ...
All semiconductors , Pots , and op amp are new product .
I know its hard to help diagnose stuff like this on a Forum , but i just thought that maybe i have overlooked something simple .
My Diode setup : 1N34a + 1N4001
                        1N34A + 4148


here's the vero diagram for reference :







Actual build below :

[slacker]

If you get large amounts of distortion and the pot does nothing, then probably either the pot is damaged or not connected properly.
If you get no distortion and the pot does nothing then it's probably a short somewhere between pins 1 and 2 of the opamp or a bad connection around C2 and R4. Either of those things basically make the opamp just act like a buffer with no gain.
The other thing it could be is the layout is missing a cap in parallel with R2, there should be something like a 47uF or 100uF cap there. Without this I don't think it will work properly.

[HOTTUBES]

The drive pot was replaced late last night , and still does nothing , there is no drive at all...zero !
I'm going to recheck the wiring to the pot , & reflow all the solder's on the backside of the board .

To the best of my knowledge , there is nothing missing on this layout , it has been verified .

Would a bad op amp give you this condition ? I may swap it with another just to see ....

[HOTTUBES]

Replaced op amp with new 4558D - no change .
Reflowed all solder's on clipping diodes , op amp socket , R6 ,C3 , C2 , R4 ... - no change
Removed R4 to verify 4.7k - checks out good .
Removed R5 to verify 47k - checks out good .
Removed C3 to verify 47pf - checks out good.
As stated above , i replaced the drive pot late last night as well . - No change
No solder bridges , visually checked , as well as with a DMM set on continuity .
All cuts to board layout verified with DMM set to continuity .

[slacker]

Try temporarily sticking a big cap in parallel with R2 and see what happens.

[HOTTUBES]

What does a big cap do in this situation ?

I'll give it a  shot  & report back .....

[HOTTUBES]

Ok , so i installed a 47uf cap across the R2 resistor , and now i have some drive control , but not much .....
Wonder what a 100 uf would do etc etc .... maybe my next move ...




Thanks SLACKER !!

[HOTTUBES]

Nope , the 100 uf cap did nothing more .... very strange !

[HOTTUBES]

I noticed that this build calls for a 100K " B " taper pot , but most other Tube Screamer schematics i see call for a " A " taper pot . 

[RandomGlitch]

No one's mentioned checking the track cuts. I can see some dull pink markings on the photo, but maybe you missed one?

I always seem to miss one cut when I build on vero!

The fact that your work is very neat and nice-looking makes me think it's some "silly" mistake like that.

Pot taper won't make any difference to it working on not, just the taper between minimum and maximum.

[HOTTUBES]

Each of the red dots you see on top of my build , are the cuts underneath etc etc .
( This is how i start my builds on vero , i mark the cuts , then jumpers , then op amp placement .)
All cuts have been accounted for and checked .( but good idea , never hurts to check !)

Yes , i did just for experiment sake install a 100K A pot and it made no real difference .


It's strange though , Slacker had mentioned to install a cap in around the R2 resistor , and it did help , but still nowhere near the drive this layout should have ....

[HOTTUBES]

FYI ....

I checked my records , and i have built this layout once before ( as i thought i did ??) and i had no issues like this with that build , it went smooth with no troubles , that's what i find so weird in this case .


What the hell a'm i missing ??  Sorry . i'm starting to get a bit frustrated ...




Thanks for any help !! 

[RandomGlitch]

I know you changed the IC.. but maybe you have 2 that are bad. Can you try them in another working circuit to check?

I'm sure it's not, but could the board be shorting against the enclosure or a jack socket or something? Try moving it about to see. 

I'm sure that you know all this anyway, but perhaps we can spark of a working idea!

[HOTTUBES]

just grasping here ... but , could the diode arrangement i picked cause a problem like this ?
The build only shows a couple of clipper's etc etc , i have done this set up in my mods , and a few other overdrive builds , so i know it sounds good in those builds ...  but i'm not sure .

The last build i did like this i used 4148 / 914's IIRC  !!



1N34A + 1N4001
1N34A + 4148

Proper polarity was observed on these before installation .



Op amp Question ??

Nope , i removed the Jrc4558D that was in this build and installed it into my Modded SD1 , sounds fine there !!
So i left that well alone , and installed a fresh one in this build , no change with new 4558D ..


Shorting ?

Most likely not , see the black Velcro that lines the box around the board .  That's in there for that reason ...



Thanks for your help !!

[HOTTUBES]

I'm thinking of just rebuilding another board all together ... and keep this one for further post mortem !!
In the time i have spent back tracking & fooling around i could have easily rebuilt another one ....

[RandomGlitch]

Yeah think you're right.  Sometimes one just has to make a tactical retreat!    Maybe breadboard it first next time?

Anyway, when you DO figure it out, be sure to post just what it was!

[HOTTUBES]

Well , i was thinking that i'm going to tough it out , and continue to try and fix this one .
I hate to admit defeat !! ha !!!!
Starting over would just be quitting anyway , and that's not in my Vocabulary !!!

[HOTTUBES]

Any other thoughts on what would cause my drive pot to do nothing ??  ( See above for details ...)




Thanks for any help

[J0K3RX]

Did you try checking it against a schematic? Are you sure you built one from this same diagram? I am wondering if it may be a shotty diagram as in not verified...? Did you try it without the diodes?

[HOTTUBES]

I have used this layout once before and it worked fine from what i remember .
Try it with out the diodes you say ?   hmmmm ... I had not thought of that !!!
I just may have to give that a whirl , thanks for the tip Jim !!!!

I will report back ...