building a sort-of DI box, need assistance

[spadz93]

Let me start by saying this is my first post to the forum, so if i'm breaking any rules (and i dont think i am) then please excuse me. that being said, i'll start this off by saying yes, this is a rather ghetto-rigged project, but time is short and so are budgets (me and the band are getting a mixer to handle this soon).

My band plays to a live click track that's synced up to samples that are sent to a PA. right now, we have one long MP3 file played from an iphone thats going from a regular aux cable to a box. this box will have an input for the aux cable (1/8 female), and then that signal splits into three pins, left right and ground. the idea behind this box is to split the signal so that the side all the effects are panned to (left in this case) will be sent to a mono 1/4" female jack, so an instrument cable may pass the signal along to the PA. the side that has the click track is panned hard right is supposed to be sent to two different stereo female 1/4" jacks that have the tips bridges so the signal comes out of both sides on both my drummer's in-ears and the output to my wireless.

here is a diagram of the connections.



when just the iphone and the PA system are plugged into this box, the click doesnt bleed through to the PA output, and all is well. however, the second i put headphones in, the click (very softly, but noticeably) bleeds into the PA output. what am i doing wrong here? bear in mind i have no resistors or anything in line here, just wiring. not sure if i would need any of those somewhere in here

[PRR]

Two channels "should" use TWO ground returns.

But for simple headphones, it is sooo much cheaper to use a 3-contact plug and share the ground. If there is a little leakage, that's fine (may improve the headphone sound, since stereo is mixed for speakers and there's always crosstalk across the room).

OK, now you have two very different signals which should NOT cross-talk.

AND you are plugging in a *heavy* load, headphones, on ONE side.

While there is some crosstalk in the plug, jack, and wire resistances in your splitter, there's also common-ground resistance in the iPhone. (And it may not be simple resistance.)

My first fix-attempt would be that "bad path" where PA Out gets ground "from" the headphone jacks. Also this splitter should be *AT* the iPhone, not some feet down a wire. You have big clicks on that side, your "nice" sound should not get its ground from the clickity side.

However unless that's long thin wire, I doubt it makes much difference.

My next fix-try would be to NOT feed the headphones (and their high current) from iFone and spliter. Split, then "load gently". The PA is probably fine. The headphone side, use a headphone amp. Instead of 16 or 8 ohm load you have 10,000 ohm load on the split and the common ground. Could be 1,000 times less crosstalk.

A headphone amp can be an old Sansui hi-fi from a yard-sale (split its headphone jack for multiple ears), or a Ruby-like small speaker-amp based on LM386, LM380, etc.

[spadz93]

Two channels "should" use TWO ground returns.

But for simple headphones, it is sooo much cheaper to use a 3-contact plug and share the ground. If there is a little leakage, that's fine (may improve the headphone sound, since stereo is mixed for speakers and there's always crosstalk across the room).

OK, now you have two very different signals which should NOT cross-talk.

AND you are plugging in a *heavy* load, headphones, on ONE side.

While there is some crosstalk in the plug, jack, and wire resistances in your splitter, there's also common-ground resistance in the iPhone. (And it may not be simple resistance.)

My first fix-attempt would be that "bad path" where PA Out gets ground "from" the headphone jacks. Also this splitter should be *AT* the iPhone, not some feet down a wire. You have big clicks on that side, your "nice" sound should not get its ground from the clickity side.

However unless that's long thin wire, I doubt it makes much difference.

My next fix-try would be to NOT feed the headphones (and their high current) from iFone and spliter. Split, then "load gently". The PA is probably fine. The headphone side, use a headphone amp. Instead of 16 or 8 ohm load you have 10,000 ohm load on the split and the common ground. Could be 1,000 times less crosstalk.

A headphone amp can be an old Sansui hi-fi from a yard-sale (split its headphone jack for multiple ears), or a Ruby-like small speaker-amp based on LM386, LM380, etc.

so your saying if i take the signal thats supposed to be headphone only, throw it into a headphone amp, that it should help? just making sure i'm reading this correctly. also, should the signal being patched to the headphone amp be mono or stereo? one of the outputs to one of the headphones needs to be stereo for my drummer to hear the click in both of his ears. the output to my wireless transmitter (for arguments sake, headphone #2) can be mono, my transmitter doesnt broadcast in stereo, only mono, so it only needs a mono input.

if headphone amp is the situation, my friend has a behringer HA400 that i may be able to borrow, and if it works ill buy my own. or is there a specific feature i need to look for?

[Seljer]

Your current scheme would be actually be fine for splitting it, just put the headphone amp in between the headphone outputs and the headphones. The amp will supply the extra current recquired to power the headphones and that'll free up Iphone's relatively weak output stage

[spadz93]

my new schematic eliminates one of the headphone outputs, so its one mono out to the PA and one stereo out to what will now be the headphone amp, and then the sends from the headphone amp will go to me and my drummer. hopefully this solves the bleeding issue.


EDIT: logically thinking, i won't need a second headphone amp involved here for the PA signal since the load will be taken off the headphone side, right? makes sense since the iphone is really only designed to play music through one set of headphones, that "one set" being the PA in this case, and the other split will be amplified on its own.