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dmg

Sat Jan 23 2010, 05:56AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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How to I connect an audio source (MP3 player etc.) so that I can hook it up from a distance to an audio modulator? (requires a - and + input for the modulator, I never worked with audio jacks before, but what I want to do is to have a wire to give me about 7 feet distance between the modulator and the audio source, so what parts do I need and how do I set up this connection?
(further information: on the audio modulator, the raw input first goes through an Opperation amplifier IC and this requires pos and neg input from an audio source, so I assume 2 wires in the cable between the jack in the audio source and the jack on the modulator PCB.)
thanks in advance.

radiotech

Sat Jan 23 2010, 12:58PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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What is the usual input of the modulator now? is it stereo? Your approach would be to make up a patch cord with a plug on either end and some parts between to match the range of the signal voltage levels of the mp3 player and the modulator and mix from mono to stereo if necessary. Do you also want to use the earphone
of the player at the same time as it is connected to the modulator?

dmg

Sat Jan 23 2010, 05:35PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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the modulator is for an SSTC, and it is not connected to a stereo, the audio source is a cheap little MP3 player thats expendable.
if I caused some confusion, I ment that the jack on the modulator can be connected to the MP3 player in a simular fasion the you connect the plug of a headphone to an MP3 player, but instead of headphones, that audio signal goes to the modulator.

so my idea is 2 male plugs for the MP3 player and the modulator, one each end of the wire, the one thing that confused me though, is when I tried to modifiy an earphone wire, I found 3 wires inside, and I only need 2, (pos and neg).

radiotech

Sat Jan 23 2010, 05:55PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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The earphone has a ground (sleeve), right (ring),left(sleeve). choose right or left for the SSTC modulator, or mix left & right with
2 100 ohm resistors, Y fashion between the two unit signal wires.

dmg

Sat Jan 23 2010, 07:07PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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here's the type of connector I am talking about (picture), so if I understood you correctly, I dont use the ground wire, just the right and left?
inside the cable, I found 3 multistrand wires, green, red, and yellow, I assume that green is ground, and red and yellow is left and right, (I can figure out polarity later) will it work if I leave the green alone and only use the red and yellow for the op amp?

Hon1nbo

Sat Jan 23 2010, 07:55PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040

no, use the ground - the difference between right and left is that there are two earbuds on a set of headphones, and audio recordings make use of this for stereo sound - for example, some musicians like to put one set of instruments on a single channel rather than both, so for example the guitar might be on your left ear while the drums and vocals will be on your right. What he is suggesting is that you merge the two channels together using a resistor arrangement to create a single channel, as your MP3s might make use of separate channels and if they do and you use only one channel without merging them, you only get that channel and you won't transfer all of the music

the ground between the two channels is common, and also there is a typo in his description of the TRS (tip-ring-sleeve) connector... he said sleeve twice, the second one should be, if I am not mistaken, the "tip" but do look up the connection online just to be safe, wikipedia's page on the connector has explanations and pinouts for the common varieties of TRS connections

-your modulator is a "mono" connections meaning it only listens to one channel for audio, and if you don't care if some of the music is missing or if your music doesn't make use of both channels, just use it as is as the mono and stereo versions of the TRS connector are compatible if they are the same size, but the mono won't listen to one of the channels and if vice versa a mono source will only go to one of the two earbuds.

BTW - it is the same principal as surround sound, but only two speakers.

hope this all helps out

-Jimmy

dmg

Sat Jan 23 2010, 11:56PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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okay thanks, so I will try it with either left and ground input or right to ground input, then ill try to merge the inputs to hopefully play the entire audio file.

radiotech

Sun Jan 24 2010, 12:50AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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DajjHman is correct; twas a typo.

I assume the MP player is 7 feet away from the TC. If were in someone's hand, the TC field might find its way back
to the coil through the case, cable and modulator. The person
holding it, the cable and the modulator should be fine . Perhaps the mp3 player might be affected. They aren't too expensive these days.

dmg

Sun Jan 24 2010, 01:14AM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
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yes, but thats the reason I am using a piece of shit mp3 player that I can buy for a few bucks at a thrift store, or I can use something like a childrens keyboard or an old walkman to test the system,
as for the RF, I intend on putting the "extension" audio wire through a metal mesh hose (the interweaved kind used for industrial wires and other junk) and grounding the protective hose to protect the audio from interference from the TC.
I will not run this thing on an audio source from a computer or an expensive MP3 player, the risk is too high to fry it.
personally I preffer to run this off an MP3, as I can play actual music, rather then tones, and In childrens keyboard, the output isn't exacly of the highest quality, I can count on a bunch of distortions from the keyboard.

eniyuki

Sun Jan 24 2010, 08:05AM

Registered Member #2148 Joined: Tue Jun 02 2009, 02:22AM
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Posts: 62

any updates? i have the same problem. i dont know how to hook audio source to the modulator (schematic from reaching1. his 4mhz audiodoulated sstc) i tried yellow and red, but nothing happened. tried to swap but nothing happened. audio source is n95 8 gig.

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