Busker's Disease

[Phil Allison]

Hi,

came up against this strange affliction some time back so maybe now is a good time to report it. Busker's Disease affects guitar leads, making them behave intermittently.

You will not find any fault with a continuity tester or visual inspection of the wiring at each end - but the damn lead is unusable cos the signal keeps cutting out when plugged into an amp and guitar.

So what is the cause ?

Unlike other musicians, buskers perform on footpaths and other open spaces with concrete or tarred gravel surfaces. So, their jack plug leads get dragged across those same surfaces, wearing off all the plating on the edge of the tips - exactly where signal contact is made when inserted into a jack socket.

Under magnification, tip edges look heavily cratered - like the moon. The previous nickel or gold plating is all gone and bare brass showing through, with tiny bits of gravel and dirt embedded in it.

A good rub with a kitchen scouring pad, followed by some WD40 on a cloth will usually get them working - but this is only a temporary fix. The plugs are ruined and must be replaced.

Of course, you may not be given the diseased lead to check, but an amp or guitar that is mistakenly being blamed for an intermittent fault.

Impossible for a tech to figure it out, if nobody tells them the owner is a busker or does not bring the leads along too.



... Phil

[jurb...@gmail.com]

We the unwilling,
Led by the unknowing,
Have been doing so much,
With so little,
For so long,
We are now qualified to do anything with nothing

[Trevor Wilson]

**Had a similar experience a few weeks back. Customer said "smoke came
out of the tweeter". A little bit of questioning and I requested that he
bring the speaker, both (mono) amplifiers, preamp and the pre - power
cable.

"Hopefully, it's just a resistor in the crossover. I read it on the 'net."

Yeah, right.

This is the speaker:

http://elac.ro/FS_607_rev-hifiworld.html

Look at the close-up photo of the tweeter. The ring around the edge is
the midrange driver. The yellowish thinkg in the centre is the ribbon
tweeter (looks more like Heil driver to me). It was smoked. Easy enough
to pull apart (those whacky Krauts make it pretty easy to strip down).
Beauty, I thought. I'll order a new diaphragm, replace it and everyone
will be happy. Cost of diaphragm? I figure $3 Bucks to manufacture.
$50.00, by the time it reaches me.

Nup. I had to buy the whole fucking midrange/tweeter. $746.00 delivered.
The importer claims to have done me a huge favour on the cost. I could
not, in all conscience make a profit on the driver, so I passed it to
the client at cost.

I checked the preamp and power amps. No problems. The interconnects,
OTOH, were some wanky audiophile bullshit. I was able to simulate an O/C
on either earth or active at various times. I presume it was causing
some instability in one of the power amps.

THEN, the customer told me that he had been running the system for many
months with no problems. The fault occurred after he had purchased some
new cables...........

Anyway, I fitted some Polyswitches to both tweeters. Just in case.

Oh yeah, I told him to send the cables back for a refund.

FWIW: The speakers sound fabulous.



--
Trevor Wilson
www.rageaudio.com.au

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[Phil Allison]

Trevor Wilson wrote:


> Anyway, I fitted some Polyswitches to both tweeters. Just in case.

** I hope you know to fit those Polyswitches in series with the high pass filter and not the coils of the tweeters.

OTHERWISE, if the device ever trips, the HPF becomes a series tuned circuit and shorts the amplifier at or near the x-over frequency.



.... Phil

[Trevor Wilson]

**Thanks for the tip. And yes, I always fit them ahead of the HPF.

[Phil Allison]

Trevor Wilson wrote:

> Phil Allison wrote:
> >
> >> Anyway, I fitted some Polyswitches to both tweeters. Just in case.
> >
> >
> > ** I hope you know to fit those Polyswitches in series with the high
> > pass filter and not the coils of the tweeters.
> >
> > OTHERWISE, if the device ever trips, the HPF becomes a series tuned
> > circuit and shorts the amplifier at or near the x-over frequency.
> >
>
> **Thanks for the tip. And yes, I always fit them ahead of the HPF.

** So you saw my letter on the topic in Silicon Chip, back in the 1980s ??

BTW One tiny Polyswitch sure is *cheap insurance* for such an expensive driver.


... Phil

[Trevor Wilson]

On 27/02/2015 5:09 PM, Phil Allison wrote:
> Trevor Wilson wrote:
>> Phil Allison wrote:
>>>
>>>> Anyway, I fitted some Polyswitches to both tweeters. Just in case.
>>>
>>>
>>> ** I hope you know to fit those Polyswitches in series with the high
>>> pass filter and not the coils of the tweeters.
>>>
>>> OTHERWISE, if the device ever trips, the HPF becomes a series tuned
>>> circuit and shorts the amplifier at or near the x-over frequency.
>>>
>>
>> **Thanks for the tip. And yes, I always fit them ahead of the HPF.
>
>
> ** So you saw my letter on the topic in Silicon Chip, back in the 1980s ??

**Very possibly.

>
> BTW One tiny Polyswitch sure is *cheap insurance* for such an expensive driver.
>

**Shit yeah. The distributor reckons that the real price was more than a
grand. Still, the thing sounds remarkably good for a moving coil speaker
system. The cabinet is very well damped, with lots of bracing and driver
integration is very well implemented.

[John Robertson]

Check the 'time to open' for your Polyswitch - some values are in the
seconds, plenty of time to blow a voice coil...surface mount ones are
pretty fast, but the leaded ones are not so fast.

John :-#)#

--
(Please post followups or tech inquiries to the newsgroup)
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(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

[Trevor Wilson]

**The particular model Polyswitch is one I've used for about three
decades with Infinity EMIT drivers. These are close to the same
impedance (resistance, actually), similar construction and similar
thermal properties. I don't expect any problems, apart from the fact
that the Polyswitch may be a little aggressive. I explained all this to
the client. He and I are happy with a conservative rating on the device.

[Phil Allison]

John Robertson wrote:


> Check the 'time to open' for your Polyswitch

** There is no set time - it is a function of the degree of overcurrent.

> some values are in the
> seconds, plenty of time to blow a voice coil..

** To burn a voice coil in a few seconds implies an extreme event - not just playing music too loudly.

Small Polyswitches, with ratings of say 1 amp, trip very quickly if overloaded by a few times - as they would be with an oscillating amplifier.


.... Phil