UK to USA step down transformer buzz

[Giubanix]

Looking for some advice from someone who knows a bit about electrical stuff. I bought a 110v Little Dot headphone amp, thinking that if I used a 110v model with a step down transformer, it might live longer than a 220v version that's being fed too much voltage.

Anyway, I've only had time to listen for 2 or 3 hours last night, but it works fine and sounds pretty good even with the bog standard tubes it's supplied with. The only problem is the noise from the voltage converter. It goes from almost completely silent (just a quiet hum that you can hear from about a foot away, if you turn your ear towards it), to a loud, totally unacceptable buzz, that you can hear as soon as you walk into the room.

If I press on the casing while it's buzzing loudly, it'll stop making a noise, so I thought it must just be the plastic case vibrating, but now I'm wondering if it's the transformer itself that's making the noise, and if so, is it a sign that it's faulty and liable to go pop at any moment?

It's one of these from Maplins:

http://www.maplin.co.uk/100w-uk-to-usa-voltage-convertor-31899

If it's clearly faulty, I'll take it back, but it's a bit of an inconvenience to go back with it only to get another that's exactly the same. The alternative, if it's not faulty, just noisy, is to get a 5m kettle extension lead and put the thing outside the room in the hallway, where it can buzz away as much as it likes without me being able to hear it. :rolleyes:

Any advice appreciated.

[daytona600]

assume 110/120v 60hz us voltage we work on 50hz 230/240v

[Giubanix]

assume 110/120v 60hz us voltage we work on 50hz 230/240v

I'm not sure if you're saying that could be the reason for the noise? It randomly goes loud / quiet while it's switched on, even if the headphone amp isn't plugged into it - no mains cable inserted into the usa output socket, just the transformer plugged in and switched on on it's own.

It might be quiet for a while, then start buzzing. I go over, press on the casing or just move the unit a little, and the noise will stop.

[daytona600]

uk 50hz main frequency usa 60hz number of cycles per second
usa 60hz different frequency some items are dual voltage & frequency for worldwide use 110-240v 50/60hz
uk 230/240volts usa is 110/120volts
was this item bought from the states for use in the uk or 220v version for use in the uk @ 240volts

[StanleyB]

50Hz is within the human hearing ability. A linear transformer will be audible when being press ganged into operation. The more current it passes the louder the hum is going to be.

[Giubanix]

uk 50hz main frequency usa 60hz number of cycles per second
usa 60hz different frequency some items are dual voltage & frequency for worldwide use 110-240v 50/60hz
uk 230/240volts usa is 110/120volts
was this item bought from the states for use in the uk or 220v version for use in the uk @ 240volts

The step down transformer states: input voltage - AC 230V, 50Hz.

There's no problem with the actual amp. It works fine with no hum or anything on the headphones. Like I said, the buzzing is just from the Maplins voltage converter itself, even with nothing plugged into it.

What I want to know is, is the step down transformer likely to be faulty if it sounds like there's a giant bee in the room, or should I just accept that it makes that noise and put it somewhere I can't hear it.

[Reid Malenfant]

should I just accept that it makes that noise and put it somewhere I can't hear it.
That is the answer :cool: Just make sure it still has ventilation ;)

[Giubanix]

That is the answer :cool: Just make sure it still has ventilation ;)

Actually, I've had it switched on for a few hours so far today and the buzz doesn't seem to be getting as loud as it did yesterday. If it stays like this it'll be fine. If it decides to draw attention to itself again I'll stick it under a little telephone table in the hall on the end of an IEC extension where I won't be able to hear it.

[jaym481]

As I came from the other side of the pond, I brought quite a bit of 110/120v gear. I'll have to have a look at the step downs I use, but I swapped three, all the same value and brand, before I found one that doesn't buzz/hum. The first one was silent until I put a load on it. The second was better, but seemed to output a little high (I was getting 125+ on my Panamax), and the third has no noise, and puts out a steady 123-125v, which is a bit high, but better than the second one.

I have no idea why. The ones I use are high power (2000W), as I run my amp off it.

[sq225917]

The buzzing is likely exacerbated by other items on your mains, like the fridge pump or the washing machine. Try adding a DC blocker.

[jaym481]

Just looked again at the step-down you're using. If you are still in the Maplin return period, take it back and splash out the extra £5 for a proper step-down with about 300W output. You may even want to take the amp with you and try it out to make sure you don't get one that hums (at minimum plug the transformer in at the store - if it hums with no load, don't bother).

Those wall-wart style converters are really strained by pretty much any load, let alone 1/3 of their rated capability.

The issue may be exacerbated by noise on your mains, but the step-down itself is really the culprit - it's just not up to the task.

[Giubanix]

Actually, I changed the buzzy one for one of these Tacima ones:

http://www.amazon.co.uk/Tacima-Stepdown-Transformer-100VA-SC5328/dp/B0001NQ07I

This one is completely silent and doesn't even get warm. The first time I switched it on, I had to press my ear against it to make sure it was actually working. The Little Dot amp only uses 15w and less than 0.2 amps, so the 100w transformer should have enough to spare.

The reason I didn't go for a 200 or 300w unit, was because I read somewhere that it's drawing the full 300w or whatever, as soon as it's switched on. I'm not sure if that's true or not, but if it is, I didn't want to be burning that much electricity just to use a little headphone amp. Anyway, there seems to be no problem with the Tacima one.

[Reid Malenfant]

While a bigger transformer may have a higher inrush current when switched on, you'll only be drawing 300W from the mains with something like a 280W load.

Admittedly though, a larger transformer will have a higher magnetising current all things being equal, so no point in going too big as you will use more electricity.

[nat8808]

Looking for some advice from someone who knows a bit about electrical stuff. I bought a 110v Little Dot headphone amp, thinking that if I used a 110v model with a step down transformer, it might live longer than a 220v version that's being fed too much voltage.

I can see the logic a little bit here but I wonder if it's false economy.. Maybe you'd have a higher voltage across the smoothing caps so they have less 'headroom' to max rating and so last a little less long. Then the rectifiers might have a higher voltage to them, within their capabilites but still needing to disipate more energy than if the transformer was 230v.

Still, the amount it might shorten its lifetime and saved costs of repair might be being completely offset by the possible failure and upfront costs of the step-down transformers themselves..

I guess though it depends on whether you would get the little Dot repaired if it failed v being able to easily change the step-down without having to find a repair man. IMHO I think your costs could be higher this way overall.

And I bet you sell it on and upgrade LONG before it would fail...