Re: [AH] Troubleshooting slight buzz/hum in System-103 spring reverb

From Oakley Sound via analogue
Sent Fri, May 3rd 2019, 08:24

The copper flux band was quite common on high quality mains EI 
transformers designed for audio applications. It reduces the magnetic 
flux leakage developed by the windings. It's not a shield as such since 
it acts as a single turn outside the core to create a inverse magnetic 
field that counteracts the one developed by the core at that point.

It is sometimes connected to 0V or earth as this can help in reducing 
electric field emissions from the transformer. The laminated steel core 
is usually connected to earth and the copper band may already be earthed 
by being wrapped around it.

What you are probably hearing is magnetic coupling so I don't think any 
additional earthing will help unless the metal tank itself isn't already 
connected to 0V.

Tony

www.oakleysound.com