Geofex hum free signal splitter a/b/y box might as well be an antennna

[scookers]

I built the Geofex hum free signal splitter A/B/Y box.  Everything sounds great except for the radio interference.  i would like to get the thing working, but is it worth my time or should I move on to something else?  Are there any other options I should try?  I read something here about peeling onions and I'm crying.  I've made quite a few pedals before, but I knew this was a big undertaking when taking it on.  I'm just sick of screwing with it right now and hope someone here has some insight.  Otherwise this thing is going through a window discount tire style.

[R.G.]

I built the Geofex hum free signal splitter A/B/Y box.  Everything sounds great except for the radio interference.  i would like to get the thing working, but is it worth my time or should I move on to something else?  Are there any other options I should try?  I read something here about peeling onions and I'm crying.  I've made quite a few pedals before, but I knew this was a big undertaking when taking it on.  I'm just sick of screwing with it right now and hope someone here has some insight.  Otherwise this thing is going through a window discount tire style.

I feel your frustration. But you haven't given us much to work with.

Is it worth your time? Maybe - how bad do you need an a/b/y splitter and how little time do you have.

Are there any other options you should try? Sure. There are always options. RF interference is a problem with fairly well known solutions. How many of them have you tried?

If you're tired of it, put it down and come back when you're fresh.

In general, RF problems are cured by putting the thing in a sealed metal box that is grounded to the signal ground at one place only, and by limiting the bandwidth of the circuit.

However, these are all RF reduction measures, not elimination measures. They reduce the RF by some amount, but don't make it zero; just less than you can hear. If you happen to be located right near large radio antennas, the RF power may be larger than you can reduce it.

All these are options and variables. Take a day or two off it. Then come back and think.

[scookers]

Thanks for responding quickly.  I have already put the whole thing in an enclosure.  I isolated the jacks coming out of the enclosure and the input jack is contacting the box.  The sound is great except that dennis miller comes over the speakers along with my guitar.  I've tried the small capacitor to ground trick on the guitar input to the board.  One side seems to get more inteference than the other.  Tried the capacitor trick there too with no help.  What do you need from me to give me a few pointers?  Or maybe this is enough.  I have a few things im going to try.  I also included a bypassable mosfet booster for each amp.  Those have their own separate battery and are isolated from the enclosure as well.  I get the radio interence before those circuits. I may rewire it because the wiring is a little sloppy.  I modified the circuit to your 2012 article after I found it.  I also have a dpdt kill switch that sends the transformer primaries to ground just like you outlined in your switching scheme.  There isn't much hum with the circuit.  Its just that interference.  If you can help me with getting rid of it, it will be much appreciated.  If you need more info, let me know.  I will take pictures of the whole mess and label it if i have to.  But even some rf eliminating tips will help, hopefully.  Thanks a million for helping out!

[R.G.]

I mentioned the external RF issues because there are some locations where the external RF is so strong that it takes extreme measures to cut it down. That's a possibility, depending on where you are doing your experimenting.

But as for some direct measures:
- A cap to ground across an input can work - or it can actually increase the RF by accidentally tuning the input wires to pick up the RF better. What you need is attenuation - converting the RF to heat. You do this with resistors. One very effective way to reduce RF is to put a 1K in series with the input signal(s) and then a small capacitor after this resistor. A 47pF to 100pF cap after this 1K resistor works well. In severe cases, using a series 1K with a small ferrite bead on the wire from the jack works even better, as this adds some series inductance as well.
- Decouple your power supply with good RF measures. Many times if you have a DC adapter, the RF can come riding in on the wires as common mode RF, and this is converted to differential by rectification in the junctions in the circuit. For this, a small resistor, maybe 10 ohms, in series in the power lead, followed by a high-quality RF cap to ground, will eat up the RF. Good RF caps are almost by definition monolithic ceramic caps. Use 0.1uF, and perhaps an additional 0.01uF in parallel for this.
- If it's coming in through an input. put a small (47p to 100p) cap from signal to ground at the input jack(s) to shunt any RF on the input wire to the enclosure/shield.
- Make sure the enclosure is firmly grounded to signal ground. It's best if this is done one place, but in pedals you can usually get away with all the jacks grounding the enclosure. It helps a lot if there is one of the jacks with an external toothed lockwasher on it to bite through any paint or metal oxidation layer to actually ground the jack bushing.
- This isn't much help to you, but I include it for completeness. Limit the RF response of the circuit itself during design so it will not respond at RF. This keeps the circuit from amplifying the RF so a later circuit section can detect it into audio signal.

It's rare that some combination of these don't work, but there are always times when only throwing a salted black cat over your left shoulder while standing at the crossroads at midnight on May Day will work. Being a pen pal with an Icelandic virgin may be needed in extreme cases.

[pinkjimiphoton]

rfi almost always has been a ground issue in my experience. check your soldering for an inadvertant bridge to ground somewhere. also check your caps. bad solder on ONE connection can cause this kinda stuff.

[scookers]

Thanks for the help guys.  I have some stuff to try.  I was thinking about the star washer earlier.  I was also thinking about a bridge to ground since the problem first appeared.  May not have been lucky enough to find the problem yet either.  I will save the dead cat until my last act of desperation before I go discount tire on this thing.  I was a little angry the other night and I took a break from it.  I have 4 guitars to fix and another pedal to finish anyway.  Thanks again for the help guys!