Strange Phase90 experience

[SocraticTelecaster]

I received my very first phase pedal last week – an MXR Phase 90 block. I've never really used a phase pedal before, but I've wanted one for a long time. To tell you the truth, I thought I'd only use it occasionally, so it wasn't high on my list of pedals to acquire. But I managed to get one on a trade for a Sparkle Drive I wasn't using anymore (I have an Ethos TLC on the way). Anyway, this little pedal has made a HUGE difference in my sound. Like I said, I thought I'd only be using it every now and then – maybe for spacey Floyd-esque type sounds, which I love, but don't really use very often in a performance environment. However, I'm using it a lot, and I love what it adds to my sound, both for rhythm and lead. I play in a funk/fusion/r&b band, and the Phase90 kicks out the rhythm parts from them mix and adds the perfect, subtle texture. Add a bit of overdrive, and the leads sounds amazing too. I have it set at about 10 o'clock most of the time.

So, I have a weird story about doing the R28 mod. that I thought I'd share. I had read up a lot about this mod before the pedal had arrived, and it had received high recommendations, so I decided to do it. Now, I'm by no means an electrical engineer, but I have built a number of BYOC pedals, and I make most of my own cabling, so I know how to use a soldering iron. The resistor was, as expected, difficult to get at just with snips, so I turned the board over, carefully marked where the appropriate solder point was, and unsoldered one of the resistor legs enough to pull it most of the way out of its hole. At that point it was easy to snip off both legs of the resistor from the top. Great, I thought – that seemed easy. But when I put the pedal together – disaster: the LED would come on when the pedal was engaged, but the pedal wouldn't phase the signal. It would only pass a clean sound whether the pedal was off or on. So I took the Phase90 apart once again and closely looked it over to see if I had done something wrong. Did I pull the wrong resistor? Did I drop solder anywhere? Did I loosen something? Everything looked good, so that was weird. I next plugged the guitar into the board and then into the amp, just to see if maybe adjusting the trim pot would make a difference (you can only adjust the trim pot while playing if the pedal is out of its housing). Adjusting the trim pot made no difference at all, however. Still just an unphased, clean signal. I was just about to give up when I noticed something: when I picked the board up off of my knee to put it on my workbench, it suddenly started phasing for a second. I put the board back down on my knee, and the phasing stopped. I picked it up again, and once again got phasing though somewhat intermittently. I soon realized that I was getting the phasing whenever one of my fingers was making contact with a few of the solder points near the output jack. I would place the pad of my index finger on that group of solder points and would get phasing; I'd lift my finger, and the phasing would stop. I decided that I would get a small piece of wire and see if I could recreate the effect by locating the two pads that needed to be connected – perhaps they needed a jumper, I reasoned. So I put the board down to get the wire, but then I noticed something strange – now, even though I was no longer holding my finger against the solder side of the board, I could still hear the pedal phasing my 60 cycle hum from the guitar (I hadn't turned down the volume on my Strat, serendipitously). The pedal was working again. I picked it up, touched my finger to the solder points, and it still worked. I removed my finger, and again it still worked. I shook it a little bit, and it still worked. So I shrugged my shoulders, put it back in its case, and put it on my board, where it has been residing, trouble-free, ever since. Go figure.

[Joe Hart]

Gremlins LOVE orange pedals. You should spray paint it yellow (this repels gremlins).
-Joe Hart

[Mugshot]

hah! so this exact post in HCFX cool story bro 

maybe some cold solder joints. reheat joints you suspect arent well soldered into place. maybe taht'll do the trick.

[Fender3D]

Why the hell everybody talks about R28?
How could you state MXR called R28 the resistor allowing the feedback signal?
There are so many release of P90 from MXR and I guess when they revised the schematic they revised the BOM too.
Find yourself a copy of the schematic (or trace it down) and look for a (usually) 24K resistor feeding signal from the last OPamp to the 2nd filter stage.

[SocraticTelecaster]

I checked, and I definitely removed the correct resistor- I even looked at the band under a magnifying glass to check the colors and confirm that it was a 24k resistor before I even began the mod. Plus, as I understand it, it is only the latest revision of the pedal (the one released in the last year or so) where the r28 mod doesn't work. The earlier block scripts are all the same vis-a-vis the location of the 24k resistor.