Power amp transformer hum

[2fastgt4]

Hi there. There are ways to measure the electricity in the wall socket for how much dc you have. Then there is a formula to calculate how you need too build the dc blocker. I did read a lot about the problem in Norwegian forums. But as mentioned before, this is way over my head.
So for people that just buy a accidentally dc blocker it might be to small and not remove enough dc.

But you are also right about the audiphile trafos. But maybe people here reacts to word as "audiophile" or "high end" trafoes .

The truth is that it is difficult to make perfect trafoes. But when the quality is good the trafo will not "hum"
So if you change to quality trafos, the hum will be gone.
Of course the dc is still in your electricity net. So some high end people still believe that the best is to have dc blocker even if it is quiet.

Cheers Tommy, the design of the PCB is one I bought online. There may be capped for more blockage.

How can I test what it's blocking?

Tommy

[blackmetalboon]

As AnthonyTD said, if the buzzing was caused by DC offset, I would expect the buzzing to vary during the day.

[2fastgt4]

As AnthonyTD said, if the buzzing was caused by DC offset, I would expect the buzzing to vary during the day.

Yes, this is correct.


Tommy

[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...?


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[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...?


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[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...?


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[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?

[alcarmichael]

OK, so after a bit of trial and error tightening down the transformers really quite firmly and then loosening them; I’ve made an improvement and reduced the hum. I’ve done so rather crudely with a couple of pieces of speaker wire between the chassis and the transformers, the nuts aren’t really providing any clamping pressure on to the transformers now:



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