[JohnR]

Hugh or anyone else, any thoughts on whether an electrostatic shield on the power transformer would be of benefit? I just called Harbuch and it's only 15-20% more to get the shield.

[AKSA]

John,

On balance, it's probably worth the money.  There is a very small improvement in hum levels, all other things being equal (which they never are, dammit....)

Cheers,

Hugh

[andyr]

Hugh,

If I hear no - or, at least, miniscule - hum (with my ears right up to the speaker and the vol turned up at normal listening levels) am I right in thinking that an electrostatic shield on the toroids - which I presume I don't have - would not have given me any advantage?

Or does the electrostatic shield help to stop "powerline gremlins" from getting through into the PS?

Regards,

Andy

[AKSA]

Yes, Andy,

That sounds right.

However, an electrostatic shield around the toroids will make it much easier to build, since the routing of all the signal wires will be far less critical.  As some have found, particularly those building with timber cases, this can be a problem since hum intrusion is a real problem in some setups, chiefly influenced by layout.

Since you have steel boxes, and the power supplies are in a separate enclosure again, your layout is particularly resistant to hum intrusion, ergo, no real point in ES shields.  If the toroids are in the same box as the amp modules, very different story and good advantage in ES shields.

Cheers,

Hugh

[Carlman]

I installed a piece of mu-metal between the torroids and the rest of the amp inside the case and it seemed to make a small difference.  

The amp reproduced sound that was slightly cleaner sounding.. as in the quiet pauses were quieter.  I've never had a hum or other noise from the amp.  But, that little bit made for a little quieter background to the music.  It may have improved the actual music as well but, it was so minor I can't remember.  I would imagine shields around the torroids would have the same effect.  

-C

[Tinker]

I installed a piece of mu-metal between the torroids and the rest of the amp inside the case and it seemed to make a small difference.  

-C

Do you have a source of mu-metal sheets? It's pretty hard to come by in Oz. I had to get my hands on some about 3 years ago and it was a lot of hoop-jumping to send small sheets from scientific supply companies. Fiddly stuff to work with too! Musn't bend it...

T.

[Larry]

Magnetic shield is as important as electrostatic shield. Any signals travelling in electrical or/and magnetic fields will be distorted, in this case, the signal travelling through wires present in elctrical and magnetic fields will be distorted. Transformers emitt (produce) these two types of fields at the same time.

The interferences of transformers, (electromagnetic interference, EMI) can affect the sonic in two ways: one is to generate hum; the other is to distort the music and in most cases, to deteriorate the sonic. The hum is obvious to identify while the distortion is not so easy and most of the time the deteriorated sonic tends to be attributed to other factors.

Electrostatic interference can be tackled by earthed shield while magnetic one needs different considerations, like flux orientation.  Magnetic shield is different from electrostatic shield and more difficult to implement. What hobbists can easily do in this respect are the tranformer orientation and distance.

Mu-metal is meant for magnetic shield (most conductive metals can be used as electrostatic shield when earthed). To shield magnetism, the metal is not necessarily earthed but has to short the magnetic flux. To do this, you need first figure out the direction of the flux in question and shape the mu-metal to form a continous (closed) flux circuit to short it. Otherwise, the shield will not work as a shield and may in fact relay the radiation.

Magnetic shield is better left to the manufacturers to handle if they are willing. If you like a really clean enviroment in your enclosure, the transformer shield is best achieved through double shields with air in between. So, getting a transformer with built-in shield by manufacturers and install it in a shield chamber will do the trick, and bring the peace of mind away from EMI, if you are an extremist, as I am. (EMI is one of major concerns of system design and affects performance more significantly than people normally believe. Some special instruments can tell the presence of EMI but are not quite accessable to hobbists.)