Beware the wall rat

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Beware the wall rat

Post by ef37a »

Or in this case the line lump. For many years I have butchered the LT leads on these things when I needed certain volts/amps but the plug was the wrong size or indeed wanted to splice it directly into a circuit.

I always found that the cable was screened, I assumed to contain much of the residual 'hash' that such supplies put out. Today I stripped one back to find a single red and single black wire. No screen.

The supply was a R.S brand (NOT to be confused with RS Components) and rated at 22V 1A. So, if any of you find an odd noise in your systems, especially one that has come about after purchasing a bit of rat powered kit, an unscreened power lead could be the cause?

Dave. (that's R dot S)
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Re: Beware the wall rat

Post by resistorman »

In my repurposing and chopping of rats, lumps and warts I’ve rarely seen one that WAS screened.
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Re: Beware the wall rat

Post by ef37a »

resistorman wrote: Wed Nov 23, 2022 8:47 pm In my repurposing and chopping of rats, lumps and warts I’ve rarely seen one that WAS screened.

I don't mean the cheaper 5V things you get for powering phones and small devices like S/PDIF switches. I mean 12V at an amp and up.

Dave.
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Re: Beware the wall rat

Post by resistorman »

ef37a wrote: Thu Nov 24, 2022 8:26 am
resistorman wrote: Wed Nov 23, 2022 8:47 pm In my repurposing and chopping of rats, lumps and warts I’ve rarely seen one that WAS screened.

I don't mean the cheaper 5V things you get for powering phones and small devices like S/PDIF switches. I mean 12V at an amp and up.

Dave.

Me too :D And since almost none of them are actually grounded, I don’t know what a shield would do? :think:
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Re: Beware the wall rat

Post by ef37a »

resistorman wrote: Thu Nov 24, 2022 3:03 pm
ef37a wrote: Thu Nov 24, 2022 8:26 am
resistorman wrote: Wed Nov 23, 2022 8:47 pm In my repurposing and chopping of rats, lumps and warts I’ve rarely seen one that WAS screened.

I don't mean the cheaper 5V things you get for powering phones and small devices like S/PDIF switches. I mean 12V at an amp and up.

Dave.

Me too :D And since almost none of them are actually grounded, I don’t know what a shield would do? :think:

Thought of that too, they would find earth at their destination much of the time e.g. an AI via either USB or audio connections.

Of course, gear is increasingly becoming earth free...

Dave
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Re: Beware the wall rat

Post by Hugh Robjohns »

The screening suggestion doesn't hold much water for the reasons above. I suspect they use coax cable just because it's easier to terminate with a coaxial DC plug.
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Re: Beware the wall rat

Post by ef37a »

Hugh Robjohns wrote: Thu Nov 24, 2022 9:42 pm The screening suggestion doesn't hold much water for the reasons above. I suspect they use coax cable just because it's easier to terminate with a coaxial DC plug.

This two wire PSU HAD a co ax plug! Jeez! I can do without all this negativity...Jus' sayin!

Dave.
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Re: Beware the wall rat

Post by Folderol »

ef37a wrote: Thu Nov 24, 2022 9:46 pm
Hugh Robjohns wrote: Thu Nov 24, 2022 9:42 pm The screening suggestion doesn't hold much water for the reasons above. I suspect they use coax cable just because it's easier to terminate with a coaxial DC plug.

This two wire PSU HAD a co ax plug! Jeez! I can do without all this negativity...Jus' sayin!

Dave.

Exactly. I remember those coax DC leads - much easier to secure with a simple gland. Oh, and (of course) the figure of eight cables STILL feed a coax plug.

And another thing. I'm pretty sure that in their original transformer and fat caps form, in the UK at least, they were not floating, but earthed.
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Re: Beware the wall rat

Post by ef37a »

Folderol wrote: Thu Nov 24, 2022 10:13 pm
ef37a wrote: Thu Nov 24, 2022 9:46 pm
Hugh Robjohns wrote: Thu Nov 24, 2022 9:42 pm The screening suggestion doesn't hold much water for the reasons above. I suspect they use coax cable just because it's easier to terminate with a coaxial DC plug.

This two wire PSU HAD a co ax plug! Jeez! I can do without all this negativity...Jus' sayin!

Dave.

Exactly. I remember those coax DC leads - much easier to secure with a simple gland. Oh, and (of course) the figure of eight cables STILL feed a coax plug.

And another thing. I'm pretty sure that in their original transformer and fat caps form, in the UK at least, they were not floating, but earthed.

THANK you Will! I don't even mean the fig 8 jobs. The one I stripped had a round, quite stiff cable...THAT is why I was surprised at the lack of a screen.
(I know I am getting on but I'm not quite THAT daft...yet.)

Dave.
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