Not "aerials", not "transmitting", as no radiation takes place. We are talking about local induction fields. Given the described symptoms, most likely to be magnetic induction from the power transformer. A well-constructed belly band should help: thick, low impedance joint (minimum solder, as that has much higher resistance than copper).
Fields might be local and decrease as the -3rd power of the distance (ie. quickly), but they can nevertheless affect other loops, otherwise no transformer could exist.
Waves are a different breed, less "local" as they decrease as -(square) of the distance, but not only: they need fields to exist, but have different properties: they can transport energy without requiring any receptor at the other end, and their magnitude heavily depends on the frequency of the signal.
At 50Hz, the effective wave power radiated by any structure, be it a HV line or a huge electromagnet is absolutely ridiculous, at the µW level at best: the so-called local effects (quasi-static) dominate completely.
Elvee,
is your reply confirming that you agree with DF96 and that transformers do not transmit interference?
or
is your reply confirming that you agree with me and that we should be looking at minimising interference?
is your reply confirming that you agree with DF96 and that transformers do not transmit interference?
or
is your reply confirming that you agree with me and that we should be looking at minimising interference?
Read what I actually said in post 21: (emphasis now added)AndrewT said:
It was your misuse of terms with precise meanings in electromagnetism which I was objecting to. Audio frequency problems (apart, perhaps, from some 50/60Hz radiation from long-distance transmission lines) are about local induction, not radiation. This might seem pedantic, but lots of newbies get confused on this very point - and snake oil merchants can exploit this confusion.DF96 said:
EMI
Does that stand for ElectroMagnetic Interference?
Sometimes referred to as Electromagnetic radiation.
The E and the M cover both electric fields and magnetic fields and both cause interference and both are made worse by having aerial loop areas.
Technically they are be defined differently, but BOTH are fields and both give interference that we don't want.
Does that stand for ElectroMagnetic Interference?
Sometimes referred to as Electromagnetic radiation.
The E and the M cover both electric fields and magnetic fields and both cause interference and both are made worse by having aerial loop areas.
Technically they are be defined differently, but BOTH are fields and both give interference that we don't want.
That point was not conveyed to me.
I understood you to be saying that there were no aerials and thus no transmission and therefore no interference.
whatever....it had been a long standing practice by Japanese
manufacturers to cover their traffos with metallic shields around the cores,
at least twice around the cores,
copper banding across the windings outside the cores and end-bells...
they understood a lot and made measures to address issues....
sometimes, coming up with layouts that are pleasing to eyes conflict
with hum issues and many times the solution that really worked
for me were those that are never good to look at...
i learned this the hard way from building tube amps....
manufacturers to cover their traffos with metallic shields around the cores,
at least twice around the cores,
copper banding across the windings outside the cores and end-bells...
they understood a lot and made measures to address issues....
sometimes, coming up with layouts that are pleasing to eyes conflict
with hum issues and many times the solution that really worked
for me were those that are never good to look at...
i learned this the hard way from building tube amps....
Just have a look at the internals of a typical Japanese cassette recorder. The transfomer has steel end caps, copper belly band, and it is mounted rotated so that it causes the least magnetic stray field to the hyper sensitive playback head. High current AC wires (from transformer to rectifier diodes) could also generate stray field.
No, I made it quite clear that local magnetic induction was the most likely cause of the problem. By the way, "interference" is a term best reserved for incoming (or outgoing) RF radiation, not local induction. In a forum such as this we only have words and pictures to convey meaning, so it is best if we use words with their usual meaning.AndrewT said:
So, no aerials, no radiation, no interference (or, strictly, negligibly small amounts of each - audio wavelengths are huge* compared with audio circuit size). But lots of unwanted local magnetic induction which is affected by circuit loop area and orientation, together with separation.
* 10kHz has a wavelength of 30km, while typical audio circuits have sizes in the cm region.
I didn't see/read that as being made clear.
It still looked (to me) like you were alleging "no aerials"
I was, and am still. No aerials. No radiation. No transmission. Lots of local induction.
I guess the distinction between local near-field induction and distant far-field radiation might not be familiar to those who have never studied RF or high frequency electromagnetics. Sadly, I have even come across antenna engineers who didn't understand the difference!
I guess the distinction between local near-field induction and distant far-field radiation might not be familiar to those who have never studied RF or high frequency electromagnetics. Sadly, I have even come across antenna engineers who didn't understand the difference!
I cannot believe this was never mentioned ...guys talk to any good transformer company and they will tell you that the only thing that will block/absorb radiated hum will be MuMetal!!
I have fond memories with talking with Jack from electraprint about this problem many years ago...he told me this then and it still will work today..
good luck
Lawrence
I have fond memories with talking with Jack from electraprint about this problem many years ago...he told me this then and it still will work today..
good luck
Lawrence
Concocting your own DIY µmetal box is not really an option: each time you shear, drill or bend it, it has to be thermally treated to recover its properties.
Galvanized iron is much worst to begin with, but at least it doesn't degrade to such an extent....
Yes, but when you talk of "EM", this normally means that E and M are not separable parts, but have to be taken as a whole, as DF96 implied.
Of course, nitpickers will say that they are never separable, but in practice quasistatic approximations of pure E and pure H are perfectly operative to the sixth decimal (and well beyond for 50Hz) for most situations in an audio context.
If you really believe that aerials and things of the sort are at work here, ask yourself: what would be the effect of placing an aerial in the offending equipment, connected to a coaxial cable and another aerial 10 meters away, near the victim equipment?
If actual EM is the problem, the interference is not going to disappear: it will be attenuated by factors depending on the air to cable transitions, etc, but it will still be present. Do you actually believe that if the OP splits its equipment in parts and puts an "aerial system" between them, it will be as bad?
For shield use iron no steel.The proportion of carbon must be minimal.And the vulgar iron is also unexpensive.You can try galvanized iron.
However the best solution is up the distance, but sometimes is imposible.
However the best solution is up the distance, but sometimes is imposible.