220->12 AC voltage transformer into 120 -> 12-20 AC

Question

I bought a budget headphone amplifier Objective 2 (Mayflower manufactured), yet just realized that even power supply has a North American plug, it expects 220 V 50Hz (european voltage). I cannot return due Massdrop sales policy. Apparently compatible/recommended power supply ( 120 to 13-20 AC with 2.1 barrel plug) are not so expensive per se (<15$), yet rare and expensive to deliver (about 30 CAN). The amplifier also supposed to work from two 9V rechargeable batteries (I guess about $20), though I do not see where to insert them, probably need disassembly the device. I also have a 220 -> 110 V converter but not wise versa. So is there reasonable way to make it work besides ordering new power supply from Mayflower? For some reason unit is not expected to work with normal AC/DC converter, and requires AC-AC power supply.

The amp designer stresses out "The transformer output can be anywhere from 14 VAC to 20 VAC and at least 200 mA. Don’t use more than 20 VAC or less than 14 VAC (except for the 12 VAC transformers listed in the parts list).Do not try to use a DC adapter. "

Schematics is on: https://drive.google.com/file/d/0B52Awjeyc5zKMjRlYjlhNGItNGJlNC00ODlmLWIwM2MtNDI4ZWU4YWRjY2Y4/view

2.5 x 5.5 output plugs seems to be more easily available yet I guess it would need some plug adapter or find soldering iron.

Answer 1

Based on the information you have supplied, we can conclude that the amplifier has an internal bridge rectifier. The reason you are directed not to use a DC source is because that would concentrate all the current in only half of the rectifier, potentially overloading it.

You could try supplying DC to the battery terminals, but that might introduce noise from the power supply/line that the battery side lacks as much filtering for, resulting in more audible noise.

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Your best choice is to get an AC adapter with the right voltages. This doesn't mean that you have to buy from the manufacturer of the amplifier, though. This type of adapter is literally just a transformer in a nice case, and given that you have the specs (14 VAC, 200 mA) that is all you need to match.

• If you have a local electronic parts store (new or used/surplus) it is worth checking with them, and if they don't have it they might know where else to look.
• It is also possible that you could find a local seller of similar equipment that could supply the power adapter. For example, I'm in the US and I could get a matching adapter (except for the plug which is 2.5 mm I.D.) from Schiit Audio, for (currency converted for comparison purposes) 22 CAD.
• Other usual sources for generic cheap stuff including the direct-from-China ones.
• It looks like 16 VAC transformers meant to be hardwired are a fairly common item you might be able to find at hardware stores. I would recommend this budget option only if you are confident in doing line voltage wiring and could build the transformer into a suitable case to protect the splices that would be required — and it probably adds up to more in total than getting the proper transformer shipped given the transformer, case, AC plug, and DC plug, unless you have access to an extensive junk-box.

Answer 2

Try and get an adaptor with the right voltage and a slightly higher current if possible . The current can be upscaled higher it wont disturb the device and if all fails you can simply recoil the transformer . In recoiling the transformer you remove the iron core carefully and the simply calculate the no of turns that will perfectly step down the input voltage while retainig the output parameters . All you need do is dont tamper the output secondary windings which supplies 12v but you should un boil the primary which is set to take 240v european voltage . After un boiling it you should fold it exactly into two thereby half ing the lenght but doubling the thickness and then you recoil again and put back the iron core carefully back and connect up your new transformer will be able to use 120v american supply and give the exact specification of output the only con this has is that the method is tedious but it works perfectly well when done correctly

Answer 3

Solved my problem. According to O2 Power Supply Wiki, as "last resort" one may use a "travel" voltage transformer in conjunction with an O2 power supply, even though wiki addresses US power supply use in Europe. I checked local Chinese dollar shop and bought the cheapest $6Can 50w "travel" transformer 120->220V. It looks extremely ugly, yet apparently does the job. The headphones sound almost as good as directly from the sources: Spotify on my cell phone, Sansa Clip or Walkman mp3 players. I'd say sound from amp is more resolving/detail rich yet less pleasant, it feels like minor distortions creep in - could be cheep cable fault as well)