Power amp transformer hum

[2fastgt4]

Forgot to tell that my amplifier is fully balanced and have 4 toroidal trafos. 4 times 500va.
And I suspected first bad quality trafos since they are 20 years old. And in that case the dc blocker as mentioned above will not help.
But all 4 is quiet now.

Tommy

[Mr. C]

I would suggest finding the null point of the transformer first that's always a good place to start, every TX has one you, you just have to find it.

[Jazid]

Not necessarily poor quality, these things can develop with time in EI cores at least. Another problem is manufacturers using 'tightly spec'd' transformers which work harder and more efficiently but are more prone to hum. I've had this with MF kit, annoying it is too.

Sent from my BLA-L09 using Tapatalk

[Barry]

If the transformer noise is due to DC offset on the mains, the 'hum' will be at 50Hz. If due to loose laminations, the 'hum' will be at 100Hz.

[alcarmichael]

So, these are my transformers:

I have no idea how they rank quality wise...?


Sent from my iPhone using Tapatalk

[Bigman80]

I have a Noratel too. Mine is potted. Doesn't hum.

Like I said, in audio application, you really need silence from it.

When I first built the DIY phonostage, I could hear the vibration of the TF through the speakers. It was really bad. It was my experience that having a noisy TF like that definitely affected the sound quality.

Spending the money on the Toriody was worth every penny IMO. Obviously, there are others with other opinions but my mind is set on only buying high quality TFs from now on.

So, these are my transformers:

I have no idea how they rank quality wise...?


Sent from my iPhone using Tapatalk

[Bigman80]

Interesting. How did mechanical buzz manage to create an electrical signal in the speakers?

It was coming through the valves. I put valve dampers on the Telefunkens and it improved. I was able to feel the TF vibrate through the casework with my finger tips when it powered up.

[Bigman80]

Ah, I see. Yes, phonostage valves are sensitive to mechanical vibration. A better solution than valve dampers is to have the valve bases (or the PCB which they're on) soft coupled to the chassis rather than in hard contact.
Soft coupling the transformers is also a possibility, but they have to be secured well enough to be safe, of course.
If the chassis is steel it's possible that magnetic induction is causing the chassis to vibrate. A spacer between the transformer and the chassis would help with that.

The case was Aluminium and it really did vibrate a fair bit.

I didn't know about soft coupling the PCB, how is that done?

[anthonyTD]

Hi Alex,
Another aspect I have found affects Transformer noise to a lesser, or greater degree, is the over voltage aspect, most European designed transformers are wound for 230v these days...Here in the UK, the voltage can vary between 237v to just under 260v in some areas [yes I have confirmation of this] So, this in itself, will have a very noticeable affect on the transformer in some aplications, not to mention the higher secondary voltages, and their affect on the components, and circuitry design!
A...

So, these are my transformers:

I have no idea how they rank quality wise...?


Sent from my iPhone using Tapatalk

[2fastgt4]

Noratel is a good brand.
However also they can have the hum problem.
Special the older ones.
The newer Noratel is made better. Dc on the electricity net is more normal now then 10 years or even 5 years ago.
Now the Noratel take that in the consideration.
The Norwegian high End brand Musical Innovation made by Roar Malmin have always used the Noratel trafo. They are known to be very quiet.
A lot of people here in Norway did change to Noratel trafos because of the quality.

So, these are my transformers:

I have no idea how they rank quality wise...?


Sent from my iPhone using Tapatalk

Tommy