Ge Diodes not clipping? Zvek Machine

[guidoilieff]

Hi. I made this pedal https://3.bp.blogspot.com/-rFeRWtUpgk4/XG8jjtIvRVI/AAAAAAAAGdc/THqe1ISNrbwlZ1u7A8eCvKwvlpTIPbUpwCK4BGAYYCw/s1600/Zvex%2BMachine.png

I hear no difference with or without diodes (I tried a bunch). Is this normal?

Thanks

[garcho]

The "limit" pot is a variable resistance to ground for the pair of diodes that should be doing the clipping. if no clipping is happening, make sure that you've wired the "limit" pot correctly. The choice of diode (within reason) will not matter.

Is your signal loud? if it's loud yet there's no clipping, then most likely the "limit" pot isn't wired to ground, or there's some other wiring problem there. double, triple check.

Is your signal weak and muffled? Maybe something else is wrong and there isn't enough signal to clip. This is most likely not the reason.

It's good to post the layouts you use, but it's also good to include pics of your build, and a schematic.

[guidoilieff]

The "limit" pot is a variable resistance to ground for the pair of diodes that should be doing the clipping. if no clipping is happening, make sure that you've wired the "limit" pot correctly. The choice of diode (within reason) will not matter.

Is your signal loud? if it's loud yet there's no clipping, then most likely the "limit" pot isn't wired to ground, or there's some other wiring problem there. double, triple check.

Is your signal weak and muffled? Maybe something else is wrong and there isn't enough signal to clip. This is most likely not the reason.

It's good to post the layouts you use, but it's also good to include pics of your build, and a schematic.

I hope you can see the video https://www.flickr.com/photos/nathanwind/33541207948 Its with and without diodes.

I've checked for continuity and everything seems fine. It distorts but I guess thats the other transistors. I flipped the diodes just in case but is the same deal.


Heres the schematic http://3.bp.blogspot.com/_y4AYtND8Hz8/SGjaGMocQ0I/AAAAAAAAAL4/bh9-1etRUrg/s1600/zvexmachine.jpg

[antonis]

First of all, verify that your diodes are indeed Ge.. 

Then verify for their firm socketing.. 

(you can work for above both issues simply by measuring forward voltage drop on socket legs pads - you must read about 300mV on both directions..)

[Mark Hammer]

The Machine creates crossover distortion.  Crossover distortion does not clip the peaks of waves, but rather the sides.  That is, the positive and negative half-waves do not swing above/below the midpoint until they exceed the forward voltage of whatever is in their path.  One of the attributes of that is that signal dynamics are largely preserved, as opposed to the way in which normal peak-clipping creates a form of compression.  The diode pair near the output is intended to retain the tonal attributes of crossover distortion, but impose varying degrees of compression to increase the "familiarity" of the effect for typical fuzz users.

[guidoilieff]

First of all, verify that your diodes are indeed Ge.. 

Then verify for their firm socketing.. 

(you can work for above both issues simply by measuring forward voltage drop on socket legs pads - you must read about 300mV on both directions..)

I rewired everything and now is working. Now when I move the pcb sometimes the audio cut off so I don't know what to think anymore. Maybe the cables are internally broken? Ofcourse when I use the dmm to test for continuity everything is fine.

[antonis]

Now when I move the pcb sometimes the audio cut off so I don't know what to think anymore. Maybe the cables are internally broken? Ofcourse when I use the dmm to test for continuity everything is fine.

Welcome to the real world..
(where everything works fine under laboratory test conditions..)

First suspect should be cables, especially on soldered edges (e.g. IN/OUT jacks, PCB pads, footswitch & Pots lugs)
Right after the above come any socketed item..
(is your circuit kept powered when audio cut-off..??)

[garcho]

one of the problems with panel mount controls is that the solder can be something like a bird beak biting down on the stranded wire. check around the 3PDT, sounds like either a short or a broken wire/cold joint, do you get hum or buzzing when the audio cuts out?

[guidoilieff]

one of the problems with panel mount controls is that the solder can be something like a bird beak biting down on the stranded wire. check around the 3PDT, sounds like either a short or a broken wire/cold joint, do you get hum or buzzing when the audio cuts out?

Just dead quiet. I think its a broken wire. Power is fine, no shorts. I resoldered all the pads so I'm discarding cold joints.


Have you ever had potentiometers fail because the rivet on the legs comes loose or something like that?