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My old Sky+ box had a 9V RF output that powered my 2 way satellite distribution amplifier directly in the loft. It allowed me to watch TV in two more bedrooms upstairs.

Recently I had the Sky+ box upgraded and the 9V output is now too weak to provide the same service.

The 2 way amp (http://www.philex.com/catalogue/product/?id=901&cat=1069) has an external DC port so I can power it from the mains, but of course the adapter did not come with it in the first place. Here's a pic:

Back of device

I rang them this afternoon and they informed me they don't even sell the adapter anymore! Anyway I thought it shouldn't be too difficult in sourcing a 12V DC adapter for this device until I saw the connection on it.

It looks (and I'm 99.9% sure I've seen this written somewhere else online) that the device takes a 3.5mm audio plug! Not a normal power barrel.

Connector Close Up of Connector

I'm handy enough with soldering but I'm just not sure if what I think I can do is acceptable...

Can I take an old 12V DC adapter I have lying around here, and snip off the power tip at the end, strip back the wire and solder it to one of the many many 3.5 audio jacks I have here currently connected to various cables?

How do I check I get the polarity correct? Is there an easier way? Am I missing anything?

Thank you.

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closed as off-topic by placeholder, JYelton, Nick Alexeev, Chetan Bhargava, Matt Young Nov 4 '13 at 20:06

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on appliance repair are off-topic unless they involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. See: Is asking on how to fix a faulty circuit on topic?" – placeholder, JYelton, Chetan Bhargava, Matt Young
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Apologies if it is determined that this question was off topic. It was my intention to see HOW to connect an audio jack to a power cable, and not how to fix my device (it's not broken). The fact that an audio jack plug on a DC power cable would power this thing is just a nice by-product ;) \$\endgroup\$ – PilotSnipes Nov 6 '13 at 15:52
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http://en.wikipedia.org/wiki/Polarity_symbols - your polarity symbol shows that the center pin (or the tip/end of the 3.5mm audio plug) holds the positive charge. This means that the ring and/or sleeve (http://en.wikipedia.org/wiki/File:Jack_plug.png) will be the ground of the DC power supply.

Mono jacks will only have 2 "sections" (bottom plug in the Jack_plug.png), and stereo jacks will have 3 sections. The DC power supplies that use 3.5mm jacks for power (that I have seen) often use the mono-style jack, but a stereo jack will work fine too!

Grab a multimeter, strip the wires off the end of your 3.5mm jack - you might have 2, 3 or even 4 conductors. Use the conductivity or diode check setting on the meter (the one that beeps when you touch the meter leads together) and figure out which wire is the tip and which is the sleeve. Sleeve is ground, so you can connect that to the negative power supply lead, then connect the positive lead.

Tip for wire splicing: use offset cuts to avoid shorting! http://www.youtube.com/watch?v=9QZ3z5s9RnY

After you've got your DC power supply connected to the 3.5mm jack, use your multimeter to check that you have 12V by plugging the supply in and touching the meter leads to the sleeve and tip of your jack. If you've got 12V, you're set!

Something to watch out for is the amperage of your 12VDC supply. The amp doesn't mention how much current it consumes, only that it requires 12V... however since the output states 15mA, you could guess that the 12VDC input doesn't require much more than that. To be safe, make sure your DC supply has 100mA or 200mA current supply, and be sure to unplug it if it gets hot or starts smoking.

Good luck!

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    \$\begingroup\$ Wonderful info. I shall be attempting this tomorrow when back from work. Many thanks \$\endgroup\$ – PilotSnipes Nov 4 '13 at 19:59
  • \$\begingroup\$ Sigh.So things never go as planned. Having read your post I doubled checked my adapter to find out that it was a 2A version. Far too strong (it seems) to attach to this distribution amp. Having compared the price of getting a new adapter with postage, then snipping and messing about with the connector, I discovered it was only about 4 euros cheaper than to buy a new proper powered distribution amp and bypass all the hassle in one go. So in the end I have a new powered amp and never got to test this out. Thank you though for the answer. \$\endgroup\$ – PilotSnipes Nov 6 '13 at 15:45
  • \$\begingroup\$ Haha no worries. Keep in mind that amperage output is relative to load - even if you had a 2A AC adapter, the amp will only draw what it needs and it will work fine. Voltage requirements should match... current supply should be equal to or greater than the load. \$\endgroup\$ – emc Nov 6 '13 at 17:49
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What you want to do should work, just as you mentioned, you need to make sure the polarity is correct. Looking at the device, your center conductor should be +. So, just get your 12V power supply, cut the connector off, strip the wires and check the voltage with a multimeter. If you read positive +12V, you have the same polarity as the multimeter (common to common).

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