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UK to US wall power supply converter question...

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brokenbones:
I'm new and still learning so please bare with me. I just ordered a piece of audio gear from the UK (i'm in the US) that requires:

9–12 V (~), max 400 mA via
supplied (included) plug-in transformer connected to 230 V/50 Hz

Now the US/UK supply voltage shouldn't matter, correct? The internal PS in the device just wants to see 9-12V? Do I have that right or am I missing something? Could I just use a typical US wall wort PS? Or, will I run into polarity or cycle issues?

I do own a US to UK power converter plug which I know would be the safest route but I have some other gear that occasionally requires that converter.

TIA

johnkenyon:
The key things from your post are:
a) "a piece of audio gear"
and
b) "9–12 V (~), max 400 mA"
and probably because of (a)
c) "plug-in transformer"

The original design uses a transformer instead of switched mode PSU for a reason - they may be efficient, but they are electrically noisy.
Your average wallwart these days will be transformerless/switched mode and will spit out DC.

Use an US adaptor which matches the output of the UK one - namely 9-12V AC. The device is probably not going to be that sensitive to running off 60Hz rather than 50Hz.
If you can't find a suitable wart, then find a 0-9 (4VA), 0-12 or 6-0-6 (5VA) transformer, and mount it in a box. Choose an encapsulated transformer, and throw in a 100mA* fuse on the primary and you should be able to get away with an ungrounded plug.

*(Replace the 100mA fuse with a 250/500/630mA fuse if that's what you've got in your spares box)



Brumby:

--- Quote from: brokenbones on December 21, 2019, 08:33:56 am ---Now the US/UK supply voltage shouldn't matter, correct?
--- End quote ---
Correct.


--- Quote ---The internal PS in the device just wants to see 9-12V? Do I have that right or am I missing something?
--- End quote ---
You have that right - but there are 4 factors you need to get right.


--- Quote ---Could I just use a typical US wall wort PS?
--- End quote ---
You have that right - but there are 4 factors you need to get right.


--- Quote ---Or, will I run into polarity or cycle issues?

--- End quote ---
The input frequency (50Hz/60Hz) will not matter at all, but you have identified one of the 4 factors you need to get right.

They are:
 1. Voltage.  There is the obvious need to match a 9V requirement with a 9V supply - but you also need to be a little careful here.  Some supplies are not as well regulated as others and these can have a higher (sometimes significantly higher) voltage when the load current is low.  Such is the case with many (not all) transformer based supplies (these are almost always heavier and/or larger than switchmode supplies).  The danger here is that the voltage presented to the device is too high for it to handle and damage could result.  This problem is minimised when the voltage and current rating of the supply matches that of the device as the device will load down the supply.  This is pretty common for transformer supplies.
As a rule, switchmode supplies do not have this problem.  You can identify them by being lighter and smaller than transformer types - but if you're not sure about this, then check the mains input voltage on the supply.  If it says something like 90V-250V, then it will be a switchmode supply.  As mentioned above, there is a caveat with switchmode supplies, especially used with audio devices, and the name gives you a big hint...  Switchmode supplies work through switching a current on and off at a frequency much higher than the mains.  Switching currents can cause EMI - both radiated and/or conducted - which can sometimes creep into the audio path.  Much gnashing of teeth will ensue if this happens.
 2. Current.  Obviously, if a device needs a particular amount of current, then the supply must be capable of supplying at least this amount.  Aside from the previously stated caveat regarding poorly regulated supplies, there is no problem with it being capable of providing more current than the device requires - the device will just take what it needs.
 3. Connector.  This is a simple mechanical matching of the plug and socket between the supply and the device.  Your typical barrel connector has 3 main dimensions - internal diameter, outside diameter and length.  Get these right and you'll be fine.
 4. Polarity.  Centre positive or centre negative?  Getting that wrong could ruin your day.

johnkenyon:
The OP stated that the power supply was "9–12 V (~)"
That implies an AC output - no polarity issues, and the supply won't be regulated either.

Jwillis:

--- Quote from: brokenbones on December 21, 2019, 08:33:56 am ---Now the US/UK supply voltage shouldn't matter, correct? The internal PS in the device just wants to see 9-12V? Do I have that right or am I missing something? Could I just use a typical US wall wort PS? Or, will I run into polarity or cycle issues?

--- End quote ---

It might matter. It depends on the architecture of the power supply. Most are Switch mode but some are not. Switch mode type will usually say on them Input 100V-240VAC or something similar. Those will work in both the UK and US.
Linear type will not work correctly.And yes they do still exist and are still sold. If it says Just 240VAC then its probably a linear power supply and it will not work properly in the US .Instead of 9VDC It will only deliver around 4.5VDC.
If it says 120VAC and used in the UK it will double the output if it doesn't burn out first.

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