Stepdown transformers without electrical hum

[tanmayj]

Hi,

I'm quite confused!!!

I'm looking to recommend a 1 kVA step down for a friend of mine who's bought a Denon 1913 from the US. (wattage is 460W as per the rear panel)

I need inputs from actual step-down transformer users.

Do you all face electrical hum (from the speakers) (not the mechanical hum) when you use receivers with stepdown transformers?

Of-course I'm not talking about situations where the home earthing has an issue or the winding on the transformer has an issue. I'm talking about an ideal situation. In an ideal situation, can we expect clean sound, or anticipate some hum?

I went through three types of transformers:

1) Auto
Cheapest, simplest

2) Torroidal
Compact, lightweight

3) Isolation
Larger, costlier and safest (short on the input wont blow the amp)

Should I anticipate some hum from the speakers with any of these transformers? Which is the best one to reduce hum (if any)?

Is an Isolation transformer really worth it, or does a torroidal provide sufficient safety and clean sound?

 

[greenhorn]

if reducing hum is all you want, keep the transformer as far away from the equipment (maybe a different room) as possible to reduce EM interference

 

[marsilians]

One common source for hum is ground loops. Have you ensured there are no ground loops. Then irrespective of type of transformer you are not going to remove it.

From step down perspective I have 4 Maxine steps downs in various parts of my house and have no hum

Lastly, 1kVa is overkill for the denon. Depending on the age of the house it may trip the fuse in the mainboard. (I rectified one such case about 2 months ago for hello HFV'er by switching around his equipment and using .5kVa instead of the 1 he was using).

 

[tanmayj]

One common source for hum is ground loops. Have you ensured there are no ground loops. Then irrespective of type of transformer you are not going to remove it.

From step down perspective I have 4 Maxine steps downs in various parts of my house and have no hum

Lastly, 1kVa is overkill for the denon. Depending on the age of the house it may trip the fuse in the mainboard. (I rectified one such case about 2 months ago for hello HFV'er by switching around his equipment and using .5kVa instead of the 1 he was using).

Thanks.

1) Which ones from Maxine? The Torroids? Though they are not Isolation transformers, do they atleast have fuses and stuff which will provide some protection in case of an issue with the input side?

2) I read on the forums that we should at-least go for 1.5-2x the wattage of the Receiver to provide for sudden power-demands. I haven't been able to find out if the 460W printed on the back-side is the max. wattage or typical wattage with surges going above it. If not 1 kVa, what do you suggest? Would a 750VA be fine?

 

[Selvin]

Hi,

I'm quite confused!!!

I'm looking to recommend a 1 kVA step down for a friend of mine who's bought a Denon 1913 from the US. (wattage is 460W as per the rear panel)

Of-course I'm not talking about situations where the home earthing has an issue or the winding on the transformer has an issue. I'm talking about an ideal situation. In an ideal situation, can we expect clean sound, or anticipate some hum?

I went through three types of transformers:

1) Auto
Cheapest, simplest

2) Torroidal
Compact, lightweight

3) Isolation
Larger, costlier and safest (short on the input wont blow the amp)

Hello..

1. Autotransformer is not good for audio - avoid it.

2. Both Torroidal and Normal core transformer are functionaly same. The difference is only construction. Both will offer isolation but again it is depend how it is connected.

Suppose your / Friend house has only Single phase connection then it is a Line - Neutral connection. By default the neutal point is earthed at distribution transformer. Now if you connect your isolation transformer secondary Neutal (0 Terminal) to earth then there will not be electrical isolation. If you not connect then it is electrical floting and it is not recommended due to many reasons.

If you have 3 phase connection You may use a 415/230V single primary & secondary winding transformer and you need to connect primary between two phases and should connect secondary Neutal (0 Terminal) to earth. Which offers real electrical Isolation.

Decide yourself you need voltage reduction or isolation or both and select accordingly.

If you need compact size, Less weight and like to place near to audio gears then go with Torroidal design. Which offers less leakage flux and help to reduce noise/hum but it takes much higher inrush current than normal core trafo while switching on. So consider your input fuse / MCB accordingly.

3. Your transformer power rating should be atleast 3 times higher than the VA requirement of amp for better sounding / attack and control over speaker. In your case you required 1500 or 2000VA transformer.

 

[resthuishi]

Which offers less leakage flux and help to reduce noise/hum but it takes much higher inrush current than normal core trafo while switching on. So consider your input fuse / MCB accordingly.

 

[Selvin]

Which offers less leakage flux and help to reduce noise/hum but it takes much higher inrush current than normal core trafo while switching on. So consider your input fuse / MCB accordingly.

Torroidal design.