Voodoo Vibe clone (Pangea vibe) - radio interference

[Bret608]

Hi everyone,

I was unhappy with the boxing I originally did on my build of Brejna's Pangea vibe, and had also been getting some radio noise (what I believe is an FM station, 102.5--I live near a huge radio tower!). So I re-boxed it in a roomier enclosure and used enclosed jacks and shielded wire. I've confirmed with my DMM that the jack shields have continuity to the enclosure. Could someone take a look at this gut shot and let me know if there is anything about my wiring that could turn this thing into an antenna? The wiring scheme I used here was essentially the same minus the shielded wire, i.e. one ground point from the circuit board going to the dc jack, and one going to one of the jack shields, that is then connected to the other jack shield with a wire. Ground loop? And if so, can those pick up the radio given the right conditions?

[Bret608]

A bump and an update...I dug into this a bit and have progress to report plus a question or two.

So, I tried disconnecting the in/out jacks from each other to check for a ground loop. No change, but...for some reason I randomly plugged a plain ol' TS patch cable into the expression pedal jack and the radio interference disappeared, more or less completely! I just lost the speed control, with the speed defaulting to the slowest speed for whichever range you're dialed into on the rotary (I think because lug 2 of the speed pot is basically grounded if you do that).

I then dived into the schematic and layout diagram to try and figure out what's going on. It basically seems like this circuit either wants something plugged into the expression jack if you're wired for one, or for those two pads for the non-expression pedal version to be jumpered. I tried jumping the two pads manually yesterday by touching the ends of some alligators clips to them. It was hard to make contact and play guitar at the same time, but I think the radio noise dropped off when I did that but allowed me to still have the use of the speed (fine) pot.

Could someone else who has built this confirm I'm on the right track before I seal the deal with one solution or another? The easiest would be to just buy an expression pedal (suggestion for brands, etc. welcome!), or I could just solder those two pads together until I finally do buy one. Any insight into what is going on electronically speaking would be welcome too--looks like it has to do with lug 2 of the speed pot and how it connects to pin 3 of IC1.

[bsoncini]

You could try to just wire a pot to a stereo cable and plug it in to test.

http://www.strymon.net/strymon-tech-corner-1-anatomy-of-an-expression-pedal/

[thesmokingman]

just looking at the picture, it looks like you have two conductor shielded wire with the two conductors hooked up more than it does that you have the shielding grounded at the jacks

[Bret608]

Thanks for taking a look! I've only got the shielding on that two-conductor wire grounded at the jack ends. On the ends going into the PCB, I snipped off the shielding braid and capped it off with heat shrink. Is that what you mean?

[brejna]

Did you try to use another powersupply?

[Bret608]

I did not try that yet--at the moment I only have an Ibanez wall-wart on hand (sad, I know!). Would it be possible to connect a battery to try without desoldering anything?

I have wondered if I get RFI through the AC mains in my house, because sometimes I get the radio through my amp when using no pedals at all.

One more strange thing I noticed in my troubleshooting--if I insert a patch cable just barely into the expression pedal jack (only about 1/4 inserted), the RFI stops! Maybe it's a combination of that jack being open, plus the less-than-ideal radio situation in my neighborhood? If I decide to just try it without the EP jack for the moment and jumper the pads, do I need to remove all wires for the jack?

Thanks for you help! 

[thesmokingman]

here's what I mean:
it looks like you have two conductor wire, unless you put heat shrink on your shielding braid and that heat shrink is why it looks like two conductor wire.

regarding your expression jack ... how well is it grounded?

[Bret608]

Ah, I see what you mean! I did put some heat shrink on the twisted and tinned shielding, so I can see why it looks that way.

Good question on my expression jack grounding--it is a plastic Neutrik stereo jack (NYS212) with all three lugs switched. That third pair of lugs, the ones closest to the enclosure wall, is connected to the board ground via a wire. I thought I checked continuity in that area but will look again. I could try connecting the empty lug on that band to the input jack ground with an alligator clip and see what happens. Did I use the wrong type of jack here?

[reddesert]

I did not try that yet--at the moment I only have an Ibanez wall-wart on hand (sad, I know!). Would it be possible to connect a battery to try without desoldering anything?

Get a battery snap and solder a DC power connector plug (2.1mm inner, 5.5mm outer diameter) onto it. I have one of these that I use for testing every build, on the theory that the battery is quieter than the wall wart and may deliver less current, so it's less likely to fry things if I made a bad connection.