[CButterworth]

In the instructions for the AKSA 55,  hugh mentions that the chassis and / or mains earth can be optionally wired to the star earth.

Are there any advantages in doing this?  Are there any disadvantages?

Thanks,
Charlie

[andyr]

Charlie,

As you've no doubt figured out, the mains earth prong of the IEC socket should be connected to a chassis earth bolt (and scrape away any coating on the metal, so you get a good electrical contact).  This is for safety ... but assumes you have a 3-wire power cord going back to an earthed wall socket.  In Oz/Europe, this is standard but is not always the case in the USA.

In my case, then trying a connection from the AKSA power supply "star earth" to this "safety earth" produced hum, so I removed it.

Regards,

Andy

[CButterworth]

Andyr,

Thank-you for the reply.  I'll connect the mains earth to the chassis using a bolt and ensure that there is good connectivity by scraping away the paint.

Charlie

[blizzard]

Hi Charlie,
  My situation was the opposite.  If my star earth was not connectecd to chassis earth I had hum.  Connecting star earth to the chassis made the AKSA dead quiet.

            Good Luck,
                  Steve

[AKSA]

Charlie,

Both options - to connect or not to connect amp ground (star earth) to chassis/power - are valid and safe.  If the former, you use conventional, 'earth everything' methodology, but even then sometimes it hums, particularly when you use certain sources which are also earthed to the mains.  If the latter, you disconnect star earth from mains/chassis earth, that is, you 'double insulate', a routine approach in medical electronics where shocking the patient, even with a few trifling microvolts, is frowned upon.     Sometimes the 'double insulate' approach is the only way to fully eliminate hum, so you really have to try both approaches to see which is quietest.  Note that in ALL cases, mains earth MUST be connected to chassis, via a bolt on the chassis with all paint scraped off as Andy suggested to ensure good electrical contact.  This is ESSENTIAL, otherwise the amplifier could be quite unsafe and certainly would never pass electrical inspection.

Earthing, ground loops, hum, and other noisesome maladies are a black art.     There is no doubt correctly holding the mouth whilst applying the finishing touches is quite significant in hum management.  Hum is inevitable to some degree;  these are amplifiers, and noise is all around.  It is a matter of reducing it to inaudible levels, and if you have ever built a SET with 100dB/watt/metre speakers and Directly Heated Triodes (2A3, 300B, 211, 845), you will have experienced the worst scenario in the industry.  Books have been written on this topic, with the hapless readers left even more confused after a full and complete reading.    

Cheers,

Hugh