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O2 Headphone Amplifier GB

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#711
@MisterRogers: Please read the last couple of posts...
The GB won't stay open until christmas, just as long as necessary.
I want to get my soldering iron out of my holster as much as the other couple hundred guys.
But theres no use in rushing towards a flawed product if you can do it properly.
 
#712
Jokener has kindly obtained a 230 VAC to 12 VAC transformer and discovered it only measures 11.5 VAC with no load. That won't work for the O2.

The Mouser WAU12-200 transformer in the parts list (120 VAC input) measures 13.5 VAC on my line voltage and works fine. Most transformers achieve their rated voltage at full load with the specified line voltage. So when lightly loaded they put out higher than their rated voltage. I was expecting European transformers to do the same, but apparently they only achieve their rated output at 240 VAC input which is higher than at least Jokener has in Germany.

So it will be necessary to use a 14 - 18 VAC transformer with the O2 in countries with 220 - 240 VAC power such as:

Maplin N57AT and N58AT

MP3059 from Jaycar.

Stontronics AC-1550BS (UK), AC-1550EU (EU), AC-1850ST, AC-1850EU
 
#716
MrSlim said:
Hmm.. I just bought 15 adapters from an Ebay vendor. Would plugging it into a 110-230v transformer and measuring the voltage be a valid test? I'll also check with them to determine if they have a 15Volt version ..
Click to expand...
As long as you measure the input voltage as well as the output voltage, that should be a valid test. I don't know what "typical" line voltages are around the world. The transformer needs to produce 12 VAC at 200 mA (loaded with roughly a 60 ohm 5+ watt resistor) at the lowest line voltage users are likely to encounter. That last bit is the tricky part.

It's also worth pointing out, the higher the current capability of a transformer the lower the no-load voltage will usually be. Bigger transformers have lower winding resistance and lower losses so the manufacture doesn't need to raise the voltage as much to meet the fully loaded spec. The Mouser WAU12-200 works, in part, because it's only 200 mA (2.4 VA) and has a higher unloaded voltage.
 
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