vB Easy Archive - Need help modding 2.5mm headset for SE fast port phone (z520a)

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Need help modding 2.5mm headset for SE fast port phone (z520a)
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Posted by: atreyu

Hi all,

I've spent many hours searching here and elsewhere for help with my mod job and still am not sure how to proceed, so I figured I'd pose the scenario to the experts on this forum.

There are a few threads on modding HBH-60 & HBH-70 fast port headsets (stock with most SE fast port phones) to accept third party headphones, but they all seem to assume you want to use the microphone built into the answer button unit.

In a nutshell, I need to adapt my 2.5mm headset (Etymotic's ETY*com) to my Z520a's fast port, using an HBH-60 I've ordered. We have soldering equipment at work, and a very experienced tech friend of mine has offered to do the work, provided she knows what to solder to where.

Basically, I want to leave the answer button (and profile switch) functionality intact, but want to disable the built-in microphone and remove the stock earbud, instead wiring the ETY*com's microphone and mono earpiece into the signal path.

I'll post what I (think I) understand... would you all please chime in with "that should work" or "no, no, no, you idiot!"?

Here's a diagram of the circuit board (swiped from this post):

The left side of the board is wired to the main lead (i.e. to the fast port adapter), while the rightmost contacts go to the stock earbud. So what I'm planning to do (or have my friend do) is desolder the M+ and G- wires from the board, and splice them directly to the ETY*com's mic line & ground, then desolder the earbud from S- & S+ and connect them to... ah... ground (again?) and the ETY*com earbud?

Cutting off my ETY*com's 2.5mm plug I see three wires... red (wired to tip), green (wired to ring) and bare/ground (wired to sleeve). After a frustrating Google session I'm reasonably sure that tip=earbud and ring=mic... can anyone confirm that?

Anyone have input/dopeslaps to add?

Based on assorted Googleings I'm also reasonably sure that by doing it this way the answer button and profile switching will just work... right?

Thanks to all, and thanks for making HowardForums such a great resource!

Posted by: MR WISKERS

Red is the mic positive and the green goes to the earbud. The earbud also has a black that must be joined up with the gold (ground) someplace.

Posted by: atreyu

Quote:

Originally Posted by MR WISKERS

Red is the mic positive and the green goes to the earbud. The earbud also has a black that must be joined up with the gold (ground) someplace.

Thanks for the help, Mr. Whiskers! Now, when you say the earbud has a black, are you talking about the ETY*COM earbud, or the earbud *feed* on the circuit board? Cuz if it's the former, I'm not actually cracking the ETY*COM's earbud/mic casing open, just swapping its miniplug for the part of the HBH-60 from the circuit board on. So that would explain why I don't see a black wire, right?

So my confusion comes from the only site I found w/ wiring info on miniplugs: http://www.i-hacked.com/content/view/205/47/ -- which had this diagram:

Anyway, yesterday I had my tech friend trace the contacts on my ETY*COM's freshly-severed miniplug, and she came up with tip=red, ring=green and sleeve=ground... which led me to red=tip=earbud, green=ring=mic. I had her re-check today to make sure, and she got the same result.

Is there a chance the wires are swapped on my ETY*COM, or am I missing something more basic here?

Also, is there an easy way to check the earbud functionality without frying my headset? I tried connecting a 3.5mm-to-3.5mm cable to my iPod, playing something at low volume and touching the red & green (both alone and with ground touching sleeve) to the exposed 3.5mm plug, and didn't get any sound.

Thanks again,
Atreyu

Posted by: MR WISKERS

The wire going in to the headset has 4 wires. The green and black go directly to the ear bud. The red and gold go to a board that has resistors on it for tuning the impedance of the mic.

Posted by: atreyu

Ok, so I'm kinda back to square one here, and would sure love some more help.

Basically, when I cracked open the headset, there was no circuit board at all... just a bunch of soldered wires.

Anyway, what I had my tech friend do (with help from your post, Mr. Whiskers) was desolder the lead & ground to the built-in mic and splice them to the ety's red & ground wires, respectively. We then desoldered the L bud from its lead and ground and connected them to the ety's green & ground, respectively. Shielded the solder (unshrunk shrink tube) and connected it to the phone, which detected headset mode as expected.

In this configuration, the mic was working perfectly, but the earbud didn't work (the still-connected stock R bud did work, however). So obviously it is mic=red... I just don't understand why L bud to green isn't doing the trick. We tried swapping the bud & mic connections, then re-swapping them, and got the same results.

I've since severed the stock R bud to see if having it connected was causing the failure, but got the same results. I was thinking we'd next try adding its lead and ground to the solder joint, so both L&R bud leads go to ety's green wire, and both bud grounds join with the mic ground.

Anyone else have any suggestions / help / rebukes?

Thanks!

Posted by: atreyu

Ok, so I went ahead and tried tying the other earbud's lead in to the ety's green (earbud) wire... still the same result. Mic so perfect I could cry, absolutely nothing from the earbud.

HELP!

Posted by: MR WISKERS

Phone must be playing tricks. Ety*com earbud should measure about 32 ohms ( when checked at 2.5 mm plug ). Measure resistance of the working earbuds. This phone might be very picky about it.

Posted by: atreyu

SIGH! Yeah, seems this must be the issue. I don't actually know how to measure the impedance of the stock earbud... I have access to all sorts of equipment, though...

Anyway, seems this is mushrooming well beyond what I was hoping for... I presume the next step (on finding the impedance is mismatched) would be to inline resistors to compensate?