[OT]? Replacing 1/4" jack on amplified acoustic guitar.

[Tobiah]

I have a Takamini Classical with a preamp/effects unit
built in. I plugged in a cheap cord, and the tip came
of into the jack, which is a metal completely enclosed
unit. I don't see much hope of retrieving the offending
piece of metal, so the amp has remained unused for quite
a while.

I ordered a replacement jack that was supposed to be
a direct replacement, and indeed, it looks just the same.
I soldered the new jack on with care. I made nice clean
joints and everything looked great.

Now, the effects unit is supposed to power on when you
insert something into the phone jack. This fails to
happen now. I tried fresh batteries, but no luck.

The audio jack is wired to a stereo 1/8" phone plug
that plugs into the effects unit. I unplugged that
phone plug and tested tip/ring/sleeve, which all
tested good going out the the 1/4" jack which I stuck
a TRS cable into for testing. There are no shorts, and
the tip and ring connect distinctly to their counterparts
at the 1/4" end.

But the effects unit will not turn on. What does it expect
to see? Normally, I can plug anything into the 1/4" jack,
and its presence turns on the unit. Now, no dice. I'm
wondering what to try now. What is it that normally turns
the effects on? I wonder whether I shorted the wrong pair
in the jack by having that rogue tip stuck in there for so
long.

Thanks,

Toby

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[None]

"Tobiah" > wrote in message
...
> I have a Takamini Classical with a preamp/effects unit
> built in. I plugged in a cheap cord, and the tip came
> of into the jack, which is a metal completely enclosed
> unit. I don't see much hope of retrieving the offending
> piece of metal, so the amp has remained unused for quite
> a while.
>
> I ordered a replacement jack that was supposed to be
> a direct replacement, and indeed, it looks just the same.
> I soldered the new jack on with care. I made nice clean
> joints and everything looked great.
>
> Now, the effects unit is supposed to power on when you
> insert something into the phone jack. This fails to
> happen now. I tried fresh batteries, but no luck.
>
> The audio jack is wired to a stereo 1/8" phone plug
> that plugs into the effects unit. I unplugged that
> phone plug and tested tip/ring/sleeve, which all
> tested good going out the the 1/4" jack which I stuck
> a TRS cable into for testing. There are no shorts, and
> the tip and ring connect distinctly to their counterparts
> at the 1/4" end.
>
> But the effects unit will not turn on. What does it expect
> to see? Normally, I can plug anything into the 1/4" jack,
> and its presence turns on the unit. Now, no dice. I'm
> wondering what to try now. What is it that normally turns
> the effects on? I wonder whether I shorted the wrong pair
> in the jack by having that rogue tip stuck in there for so
> long.
>
> Thanks,
>
> Toby

I know of two ways that 1/4" jacks are used to switch power. The most
common is to have the battery (or other) power negative side wired to
the ring or a T/R/S jack, and the return/ground/chassis wired to the
sleeve. The battery's negative terminal sees an open circuit with no
plug in place. When a T/S plug is inserted, the ring and sleeve of the
jack are are connected by the sleeve of the plug, completing the power
circuit. Much more rarely (I've only seen it once), there are switch
contacts that are closed (or opened) when the plug is inserted. These
jacks are normal [sic] in patch bays, but rare in guitars.




> This email is free from viruses and malware because avast! Antivirus
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>

[Tobiah]

I found out more. I examined the old jack, and found that I
did not get an exact replacement. Here is a photo of the
old jack:

http://tobiah.org/jack.html

There are three tabs coming out of the center, one of which
is connected to the tongue coming off the barrel. The new
jack has only the the top two connectors coming out of the
barrel, along with the tongue. I soldered the shield of
the cable to the big strain-relief tongue, and the R/L to
the other pins from the center.

I still can't figure out what the inside wiring is like. I tried
connecting a stereo plug to the jack and shorting pins here and there,
but nothing will turn on the amp.

Thanks for any help.

Toby

> I know of two ways that 1/4" jacks are used to switch power. The most
> common is to have the battery (or other) power negative side wired to
> the ring or a T/R/S jack, and the return/ground/chassis wired to the
> sleeve. The battery's negative terminal sees an open circuit with no
> plug in place. When a T/S plug is inserted, the ring and sleeve of the
> jack are are connected by the sleeve of the plug, completing the power
> circuit. Much more rarely (I've only seen it once), there are switch
> contacts that are closed (or opened) when the plug is inserted. These
> jacks are normal [sic] in patch bays, but rare in guitars.
>
>
>
>
>> This email is free from viruses and malware because avast! Antivirus
>> protection is active.
>> http://www.avast.com
> It's not an email. Clueless advertising for Avast doesn't instill
> confidence in their protection.
>
>>


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[Tobiah]

I got the offending plug tip out of the jack by
slamming it on the desk many times. Put that jack
back into the guitar, and I'm all working again.



On 6/7/2014 11:32 AM, Tobiah wrote:
> I have a Takamini Classical with a preamp/effects unit
> built in. I plugged in a cheap cord, and the tip came
> of into the jack, which is a metal completely enclosed
> unit. I don't see much hope of retrieving the offending
> piece of metal, so the amp has remained unused for quite
> a while.
>
> I ordered a replacement jack that was supposed to be
> a direct replacement, and indeed, it looks just the same.
> I soldered the new jack on with care. I made nice clean
> joints and everything looked great.
>
> Now, the effects unit is supposed to power on when you
> insert something into the phone jack. This fails to
> happen now. I tried fresh batteries, but no luck.
>
> The audio jack is wired to a stereo 1/8" phone plug
> that plugs into the effects unit. I unplugged that
> phone plug and tested tip/ring/sleeve, which all
> tested good going out the the 1/4" jack which I stuck
> a TRS cable into for testing. There are no shorts, and
> the tip and ring connect distinctly to their counterparts
> at the 1/4" end.
>
> But the effects unit will not turn on. What does it expect
> to see? Normally, I can plug anything into the 1/4" jack,
> and its presence turns on the unit. Now, no dice. I'm
> wondering what to try now. What is it that normally turns
> the effects on? I wonder whether I shorted the wrong pair
> in the jack by having that rogue tip stuck in there for so
> long.
>
> Thanks,
>
> Toby
>
> ---
> This email is free from viruses and malware because avast! Antivirus
> protection is active.
> http://www.avast.com
>


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[John Williamson]

On 08/06/2014 20:15, Tobiah wrote:
>> But the effects unit will not turn on. What does it expect
>> to see? Normally, I can plug anything into the 1/4" jack,
>> and its presence turns on the unit. Now, no dice. I'm
>> wondering what to try now. What is it that normally turns
>> the effects on? I wonder whether I shorted the wrong pair
>> in the jack by having that rogue tip stuck in there for so
>> long.
>>
The unit will probably be looking for a short circuit between two
normally open internal contacts caused by inserting the jack into the
socket to turn on. One simple way to do this has one side of the power
supply connected to one of the contacts, with the supply current passing
when they are closed by the plug being inserted. If these contacts have
been bent out of shape or otherwise damaged, they will not short
together, so the unit won't power up.

You need to open the case and check these contacts, which (and it's a
slim chance) may be in the form of a microswitch which is operated by
inserting the jack.

The *really* cheap and nasty way has a contact on each side of the
sleeve connection, and the operating current passes through the sleeve
from side to side.

Not hard to fix once you get in. You might even find it preferable and
possible to install a proper switch if there's room, or if you run it
off a wall wart, just wire it to be always on when the power's connected.
--
Tciao for Now!

John.