Crunchbox - unusual 1N4001 problem!

[Cortex]

Hello good people!

I built the Crunchbox using this layout => http://1.bp.blogspot.com/_XBLxtjUxez0/SZeFbE1n3MI/AAAAAAAAAAM/BLgvif_C5k0/s1600-h/crunchbox.bmp [but chose not to include the jack orman anti-pop circuit on the down right]
Actually I built a dual pedal, CB + SHO, decoupled the power supply like this => http://i11.photobucket.com/albums/a158/malexc/PowerDecoupling.jpg
And for a while everything was working GREAT, I was amazed by the quality of the distortion, this time I used premium parts, Panasonic electros, Xicon and Wima caps, genuine LM833 op-amp, and others...but then all of a sudden it started to fuzz! I quickly discovered it is because of the sudden voltage drop I've been experiencing. I was no longer getting Vcc on the 8-pin of the opamp, but less! Ok so I checked EVERYTHING a million times, checked the resistance of every resistor, everything is fine.

Last thing I checked was the diode. All of a sudden, I was getting aproximately 0.6V less over the 1n4001 diode. I tried 3 other diodes, the problem persists. I tried 1n4148 as a polarity protection, the same thing happened. It reduces my Vcc voltage for aproximately 0.6V just like a voltage drop. I checked every part that could be near the diode or in any way connected to it, I changed the two 100uF electros, nothing works. I just can't get the uninterrupted voltage across the diode.

Any thoughts? I just can't believe it.
It could suggest that something else is wrong with the circuit but that's almost impossible to me, cause it was working for a couple of days SO WELL.

Hm, one thing also comes to mind...I was testing the pedal while it was working so epicly well with my stable and filtrated power supply, and the friend I gave it to for a day played it using a BOSS Dc power supply. I saw that adaptor and it has no polarity switch, so that's not the possible cause.

The IC voltages are something like this

pin 1 - 4.5
pin 2 - 4.5
pin 3 - 4.2
pin 4 - 0V
pin 5 - 4.5
pin 6 - 4.5
pin 7 - 4.2
pin 8 - Vcc

those pins 3 and 7 do stand out a bit, but I don't know how relevant that is. My major problem is that something is influencing the polarity protection diode to reduce my supply voltage and I cannot for the love of god find out what!

[birt]

http://www.kpsec.freeuk.com/components/diode.htm

see forward voltage drop.



so if the diode was already there and the circuit suddenly started acting strange it doesn't have anything to do with the diode.

[Earthscum]

Does the pedal do it when it is all alone in the chain and it's the only one using the power? Not too clear on that part.

Typically, you will get .6V less (read birt's link) than PS. If you isolate the pedal and it does it on it's own, recheck all your solder joints, and of course make sure the electros are rated above your power supply.

I wasn't paying attention and used a 3.3V electro (recycle from a board) for a supply filter cap on my bread board. It started boiling inside (actually sizzling sound, but it's boiling, lol). It started getting a bit bulged by the time my tank caps finally discharged. I generally won't use anything less than a 16V rating for my caps. anyways...

solder joints, make sure nothing is shorting out inside the case (I fought my KMD Phaser on this for almost a year until I realized a pot was touching a leg through chipped paint). Solder bridges can do the same thing. If you have some close traces, the flux can contain enough residue (dirt, copper, tin, etc) to make connections you don't want, or create capacitive connections between parallel traces. Clean board is happy board, lol.

If you play with the back open and get it to start acting up, grab your DMM, flip it over, and check for voltages right then and there. You already know what they SHOULD be, so you can make a quick mental note if something seems off by a significant amount (half volt difference or so, I don't think, would be something significant, unless it's the ONLY odd value you come across).

Good luck, and if you don't track it down, maybe post a picture or two and someone here might see something you missed, or spot something we all miss (happens all the time!)