[sdiy] Weird Phaser issue

[Sam Ecoff]

Hi Guys (I mean that in the gender-inclusive way),

First, a warning and a disclaimer: I'm asking for help regarding a module that I built and sold to someone. So yes, I am about to materially benefit from your assistance. I understand and respect that some of the members of the list would prefer to know this up front.

So.... I have a customer in Japan who bought an MFOS phaser from me last year. He encountered some difficulties with it after removing it and reinserting it from a frac rack while it was on, accidentally shorting the PCB against the front panel of an adjacent module in the process. He sent it back to me, I swapped out two of the 13700's and two of the TL072's, and better matched the levels of the two outputs (with some kind help from Ray Wilson) and then put it through some rigorous testing. I spent about four hours testing it, making sure it was perfect. All of the issues it displayed when it came to me were resolved. Those issues were: louder output from one audio out than the other and a moment of silence when the internal LFO's waveform was switched.

Upon getting the module back, the customer told me that the problem had not been resolved. The amount of modulation seems to "jump" at various points. This is the case both when using the internal LFO and when using an external CV source. The module doesn't exhibit these issues while in my possession, which makes it an exceptionally difficult problem to diagnose and troubleshoot. I've uploaded a .wav file sent by the customer of the module's behavior:

http://www.samecoff.com/mp3s/PhaserInternalTri.wav

The test conditions were as follows: the module was powered by its own Blacet PS500 (i.e. nothing else on that supply) with a saw wave as the input.

There are two possibilities which occur to me. First, it's possible that there's something happening to the module in shipment which is changing its functionality when it arrives. Has anyone here heard of such a thing? The module was shipped back in an anti-static bag, but is there any possibility that some of the security scanners may have damaged one or more of the components? I dunno... perhaps a shot in the dark. Second, I know he's using a Blacet PS500, but I seem to recall that the mains voltage in Japan is only 100v as opposed to our 120v. I don't know what the customer is using as a step-up transformer or if that would make any difference. 

Thanks in advance for any light any of you brilliant people can shed!

:-)

Sam E.