A question for someone with electrical knowledge.

[Richardl]

I've got one of these that I got from the US. http://www.abt.com/product/23885/Sonance-AL1.html

Problem is the transformer seems to make electrical noise on my hifi.

I was wondering if it was possible to change the 12v transformer for a UK one, I'm having trouble finding one, as the cable to it has positive, negative and something called 'com' (which I assume is an earth). The transformer looks this.....

[StanleyB]

Can you post a picture of the power supply DC plug?

[goraman]

Com is for common ground, it sounds like what you have is a ground loop.
try plugging that switch box into an out let on another circuit.
If it still hums it's because the transformer was made to run at 60hz. and UK uses 50 hz sign wave.

Can you just eliminate the switch box all together?

[Richardl]

Can you post a picture of the power supply DC plug?

I have, that's a photo of the back of it.

[Richardl]

Com is for common ground, it sounds like what you have is a ground loop.
try plugging that switch box into an out let on another circuit.
If it still hums it's because the transformer was made to run at 60hz. and UK uses 50 hz sign wave.

Can you just eliminate the switch box all together?

The device lets me plug my dac and my processor straight into the power amp, it automatically switches inputs when my dac is switched on. All the plugs around my hifi are on the same circuit.

[StanleyB]

I have, that's a photo of the back of it.
What you posted is the label on the back of the power supply. Is there a DC plug or not?

[Richardl]

What you posted is the label on the back of the power supply. Is there a DC plug or not?

Sorry I misunderstood, it's hard wired into the device, halfway along the cable is one of these connections.

[StanleyB]

A 12V dual polarity PSU is not particularly easy to find. I paid quite a bit for a 15V one from Rapid Electronics.
You might have to look at building one from a kit.

But getting back to the hum: Connect the bare ends of a piece of insulated wire between a screw on the case of your new gadget and the case of your amp. If you are lucky it is just an earth loop problem that you have, and the piece of wire I suggested will in most cases solve the earth loop.

[Richardl]

A 12V dual polarity PSU is not particularly easy to find. I paid quite a bit for a 15V one from Rapid Electronics.
You might have to look at building one from a kit.

But getting back to the hum: Connect the bare ends of a piece of insulated wire between a screw on the case of your new gadget and the case of your amp. If you are lucky it is just an earth loop problem that you have, and the piece of wire I suggested will in most cases solve the earth loop.

I've had a quick look for one of those transformers with no luck yet.
I'll try the other method, when I get a bit more time.....off to work now :(

Thanks for the help.

[Dingdong]

I've got one of these that I got from the US. http://www.abt.com/product/23885/Sonance-AL1.html

Problem is the transformer seems to make electrical noise on my hifi.

I was wondering if it was possible to change the 12v transformer for a UK one, I'm having trouble finding one, as the cable to it has positive, negative and something called 'com' (which I assume is an earth). The transformer looks this.....

Where did you plug this transformer in to?

[Reid Malenfant]

Where did you plug this transformer in to?
That's what i'm wondering having had a look at it :stalks:

There is no mention of the fact that it may well be willing to work with 230V AC, in fact i reckon it's not even an SMPS & therefore in no way "universal voltage" capable.

I wouldn't try using it any more for safetys sake unless you happen to be powering it from a 230 - 120V transformer to lower the voltage before applying it to the unit in question ;)

If you are already doing that please ignore what i typed previously :)

[Dingdong]

The first thing I thought was that it might have been plugged into UK mains. That would definitely get it to make a noise.
Hope I'm wrong.

[Richardl]

That's what i'm wondering having had a look at it :stalks:

There is no mention of the fact that it may well be willing to work with 230V AC, in fact i reckon it's not even an SMPS & therefore in no way "universal voltage" capable.

I wouldn't try using it any more for safetys sake unless you happen to be powering it from a 230 - 120V transformer to lower the voltage before applying it to the unit in question ;)

If you are already doing that please ignore what i typed previously :)

Sorry i should have mentioned that, it was one of the small stepdown transformers that you plug into the wall.
It did work well with my big stepdown (2000w) i used for my US amp, but I've sold that amp now.



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[Dingdong]

Does the small step-down transformer have a power rating?

[Richardl]

Yes, I'll double check tomorrow but i'm sure it was enough.

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[Reid Malenfant]

Anything more than 10W will be more than adequate, so i think that might well be irrelevant Mark.

But you never know :eyebrows:

It might be a tad noisy being fed 50Hz as it used to 60Hz, there will be a much higher magnetising current in the units transformer due to this.

[Richardl]

A

It might be a tad noisy being fed 50Hz as it used to 60Hz, there will be a much higher magnetising current in the units transformer due to this.

That sounds like the problem, even when the cables weren't plugged into the device.......but it was still plugged into the wall behind the hifi, i could still hear it buzzing away through my amps.

[Dingdong]

Did it make a noise using the bigger step down transformer?

[Reid Malenfant]

If the PSU wasn't plugged into the device then there is no way it could be from your system or amplifiers, it must be from the PSU itself & probably is due to the mains frequency.

Think about it, if it's not plugged into the device it can't power it up & can't induce any hum into the system ;)

Sounds like you need a different PSU. While +/- 12V PSUs are kind of thin on the ground (i looked earlier on fleabay) there is nothing stopping you using two 12V PSUs to get that +/- 12V DC ;)

[Richardl]

Did it make a noise using the bigger step down transformer?

No it didn't .........please don't say get another one of those transformers :-)

I might try experimenting with different positions with the box, when i get a bit of time.
I've got a very strange setup here.......its all in-wall and all the stuff is quite close together.

[Reid Malenfant]

No it didn't
:lol: Are you sure it's not the smaller step down transformer that is making the noise?

[Richardl]

If the PSU wasn't plugged into the device then there is no way it could be from your system or amplifiers, it must be from the PSU itself & probably is due to the mains frequency.

Think about it, if it's not plugged into the device it can't power it up & can't induce any hum into the system ;)

Sounds like you need a different PSU. While +/- 12V PSUs are kind of thin on the ground (i looked earlier on fleabay) there is nothing stopping you using two 12V PSUs to get that +/- 12V DC ;)

Sorry. What i should have said is ......the audio cables weren't going through the device. It was still powered up using the transformer.
If just the psu was plugged in(without the switch box), there was no noise.

Im not sure how you'd get it to use 2 transformers?

[Dingdong]

That's what I was thinking. Would it be a massive pain in the arse to use the larger transformer?

[Richardl]

That's what I was thinking. Would it be a massive pain in the arse to use the larger transformer?

I don't have the larger transformer anymore .....it was 2000 watts, so wasn't too good for the electricity bill.
Plus it cost about £50 .........slight overkill i think.

[Dingdong]

The thing is that if it didn't make a noise with the larger transformer and it made a noise with the smaller one then the transformer seems to be the problem.
Is the smaller transformer new?

[Richardl]

The thing is that if it didn't make a noise with the larger transformer and it made a noise with the smaller one then the transformer seems to be the problem.
Is the smaller transformer new?

I had 2 new ones......i think they were both 50 watt.
The bigger transformer had a 50/60Hz output ......maybe its possibly that

[Dingdong]

Do you get the same noise with both of the new ones?

[Richardl]

Yes I did, it seems the device itself isn't making the noise, it's the devices PSU.

[Richardl]

Also what puzzles me, it's only a 2 pin US plug, where does the earth go, maybe it just is wired into the positive or negative?

[Reid Malenfant]

It doesn't need an Earth on the manis side as the whole thing will be what is known as "double insulated". You only need a safety earth if the thing itself has a metal chassis. If it's plastic then it won't need an earth as long as it's double insulated ;)