Why the isolation transformer will getting hum sometime

Hi there,

Thank you to who reply my question.

My question is why the line ac isolation transform will getting hum sometime.

Most of time it's would not hum at all

It's due to ???

1. phase shift of the ac supply ?
2. voltage vary ?
3. voltage drop below or above 20% of the design operating voltage ?

4. mechanically induced ? EMF ? high level ac noise ?

More info about my isolation transformer

Single 4000VA transformer
input is 0V 240V
outout is 240V 0V 240V
load about 500VA

Thank you

Han

 

Han, is your iso tranny Torroidal or E frame?, torriodal is far better at 'coupling with the mains' than multi cored units (e-frames) sometimes this causes the humm, also where it's mounted, e frames also generate 40 times the rfi than torroidals, the T's also can 'exchange hum' from other transformers with in the isolated group, IE they couple wit the tranny in the amp/cdp or what ever, rare but it does happens, have you checked the Phase when the hum happens?.
Voltage vary, I have personal seen a low in the UK of 218.7 v to a high of 253.3, never had a hum through the isolation transformers we use.
Also check the isolation ground in the transformer too. not much, but it might help. Wm

 

Hi wadia-miester

Thank you for reply.

The transformer build as EI form factor, around 40kg with the casing.


The T's ground is okay.
what will happen if the T's not ground properly ?

the phase is not check yet. needed scope to check coz I do not have a line voltage monitor.

anythings else I can check for ?

and here hard to get a ring (torriodal) isolation for 4000VA.
Han

 

The main purpose of an isolation transformer Hans is to 'electrical isolate you from the possiblity of electrical shocks by isolating a channel so if you accidently come in to contact with it, youshould be realitively safe, we've had some here that we 'earthed through one of the a/c lines interesting feeling through the equipment .
You would need to see if the phase inverts when the tranny hums. also try placing it on concrete slab or similar, slip under some 19mm mdf and an inner tube instant cheapo seimic sink Wm

 

A none technical response......

I've heard Iso T's hum when things like dimmer switches are used within the listening environment. Also when external interference on the mains, exceptional industrial processes.

I've never had mine hum audibly but it does vibrate [probably 50hz] to a small degree.

Oh yes mine's a Lynwood Advanced.

 

Thank you,

Now I am add in a 30A balance torriodal coil before the isolation transfer to suppress those unknown 'noise' since yesterday.

Somehow I still waiting the T's to hum again, usually it's happen 12 am or 6 am. (time duration ~ 30 mins)

But after added the balance torriodal coil, I lose some bass and realization of the sound stage. May be the system need to run in again.

I thank you for all idea and experience you're shared.

I will let's you know the result later.

Hello there and Happy New Year,

Hi wadia-miester, the record show the voltage vary not causing the T to hum after 15 day voltage measured.

So, any idea guys.

Hi Guys,

Happy New Year, I am back.

May you can came out some help about this after the you view the power supply from the scope :JOEL:

 

The Condition of the power supply from the main supply
time duration 15 ~ 30 mins

 

The condition of the power supply after Isolation Transformer.

But the down egde have a small cut.

 

Hans, good stuff mate, now you've done this, what effect has it had on the sound, cleaner upper frequencies, more detail, but has it lost any drive?, are the dynamics ok? whats your verdict sir.Wm

 

Hi wadia-miester,

As you wish, most of the things are improved.
Yes, cleaner upper frequencies, more detail and realization at sound stage, bass became lower and deep.

Yes, the dynamics of the system are okay (with or w/o T may be T is 4KVA)

But I had try on two T one 4000VA for amp and 2000VA for CD player, whats you're find out - more bass, dynamics and open sound stage.

Any one try with on-line UPS (greater than 4KVA) with your system ?