how to make pnp fuzzes and digitech pedals play nice together?

[pinkjimiphoton]

houston, we gotta problem...

greg and dino worked up the xp ALL, and greg built one up for me on my xp200 modulation pedal.
i was having some glitches happen, that were cured by doing a factory reset.

dino knows i use pnp fuzzes, and said he'd had a problem with them and his xp..  so i set out to check it out.

ok, i have confirmed this...there's a definite issue with PNP fuzzes.. i just tried my umi buzzbox, my fuzzface, my liberal komrade and buzzaround...all pnp's....with the xp all.

every single one caused problems, and made the xp reboot. i think i sussed the problem out.
i haven't tried the solution yet, so first let me describe the problem.

the thing works GREAT when the fuzz is engaged. if bypassed, works, if ya kick the fuzz on, it works.
but...

when ya kick the fuzz off, it makes a weird, very loud noise that sounds like an explosion...then the xp mutes, and goes back to whatever it was set to before the glitch.

all of these boxes  (my fuzzes i mean) are wired so that the input is shorted to ground in bypass, to minimize noise leakage.

what i postulate, is the glitch is caused by the pnp's positive ground being discharged to the shared ground between the two pedals...

the negatively charged caps in the fuzz discharge to a positive ground plane in the fuzz..the ground being positive connects to the case of the effect so you get a faraday cage around the circuit to prevent rfi and noise and stuff.. but the xp has a NEGATIVELY grounded chassis.

so when you stomp the switch to turn it off, it discharges the caps in the fuzz to ground...which is shared between the pedals via the shielding in the patch cords between the input/output jacks,...

and shorts out the xp.

there's two ways i can think of to combat this...

either disconnect the ground option in bypass of the effect, so the board is always "on"...

or completely separate the shield of the box from the cct using isolated jacks, and "floating" the ground of the pnp pedal....but here's the thing...you lose the faraday cage, and you still share the floating ground between the pedals. to me, ya need that shielding in the high gain fuzz anyways,
so the first option....leaving the fuzz board always "on" may be the best option.

anybody got any thoughts, better ideas or maybe a solution? i also built a tb loop pedal with a volume on the output for the xp, but had noticed glitches still the other nite..

how the hell do you isolate two polar opposite "grounds" and make these things play nice?

[pinkjimiphoton]

ok, i went back and tried again, disconnected the ground pad for the circuit board on the fuzz's switch.

makes no difference. as soon as i kick in the pnp fuzz, the xp reboots. and sometimes hangs. pnce it comes back up, it will work...as soon as i bypass, wango...same deal. reboots the xp.

so my suggestion is that we warn peeps that pnp fuzzes and these things may not be able to play nice together..

there has to be a way, short of an iso transformer, to make these things work well together.

now i understand also why my fuzzface and whammy pedal can't be used together... but i think the different grounds are the problem.

the whammy dumps a lot of noise onto it's ground...which is the ff's positive.

the fuzzface picks up a lot of rfi etc...and dumps it on it's positive ground, which of course causes interference with the digitech, cuz obviously, that's the positive of the digi.

so...ya generate a bunch of noise, amplify, and bleed it back in a hellacious feedback loop.

all avoidable completely with npn equivalents of the pnp devices.

oy...

makes my head hurt.

[pinkjimiphoton]

FWIW,

pedals with a combo of pnp and npn seem to be fine. it's only the pnp's that cause the problem.

any ideas? anybody?

[seedlings]

On my pedal board I have a PnP fuzz and a PnP rangemaster in front of a DigiTech Expression Factory EX-7 and a JamMan Delay.  I don't have any problems.

Both PnP pedals I wired the DC jack (no battery) like this:




From http://www.muzique.com/lab/fuzzface.htm

This is not likely, but... you are using the input jack to the pedal?  My pedal has an input jack and right next to that the external footswitch jack.

CHAD

[pinkjimiphoton]

definitely worth looking into, mine is the same but with a much smaller cap ,,, 100u instead of 1000... on my primary face, anyways.

maybe i should just use a charge pump's negative output.

the older xp's  don't have an external input, it's plugged in right.

every pnp pedal i've tried, same thing.

pnp/npn pedals are fine, as are npn's...only the pnp's seem to cause the issue.

[Gus]

Did this happen with a stock XP before the changes.

Do you have a battery filter caps in the PNP  circuits?

[pinkjimiphoton]

hi gus,
i never tried it stock with the pnp's before the mod, gonna try my space station out tho and see if it happens.

i can't use my whammy iv live tho, it doesn't re-boot it, but there's so much background filth that comes in as soon as i hook it up, i can't use any fuzz or even my wah. it has no problem with the other pedals tho...if i take my pnp ff out of my board, the noise goes away.

i'll be gone most of the day, so i don't know if i'll get much of a chance to dicker around with it for a day or two.

some of the fuzzes have battery filter caps, some don't. doesn't seem to really matter.

all of 'em are run on AC generally, usually with a one spot or something equivalent.

[pinkjimiphoton]

ok, i tried it with my stock xp300 space station.

exactly the same symptoms, other than it didn't reboot all the way. i had to factory reset it to clear it, but it survived.

tried it with my modern whammy iv....it popped a bit, but worked...no glitches.

i should note that there is NO audio when this happens...either the fuzz (probably not) or the xp (more likely) seem to mute until either the xp reboots, or a cap charges in the fuzz somewhere.

very, very weird.

any more thoughts guys?

[pinkjimiphoton]

ok, played with it some more, and at dino's suggestion tried a buffer between xp and fuzz.

some success with that.. it doesn't make the xp reboot if the buffer is there, but the switching transient is still pretty explosive.

it may be the buffer i used..not sure, it's just a 3904 and a couple parts i threw together a year or so back. so...some improvement, but still
need to find a solution...figuring if it's happening to me, it may happen to someone else, too.

fwiw, the stock xp(300) didn't have as extreme of a switching glitch as the modded xp, once the buffer was between the fuzz and the xp.

[Gus]

Next thing to try

-9VDC power PNP FF etc with battery power
NOT connected to an external power supply or +9VDC to -9VDC power supply circuit.

Not having a drawing of the effects and how they are connected and powered makes it harder to figure out what is happening.

[R.G.]

Gus is right, as usual. We need to see a drawing of how the power, signals, and grounds are connected in the various effects.

[R.G.]

Oh, and do all of the effects have pull-down resistors that keep input and output caps at 0Vdc when switched in and out?

[Gus]

pinkjimiphoton

Do you have a drawing of the grounding and powering of the PNP and Digitechs?
Did you try battery only for the PNP?