Polk SDA-2 and Nakamichi 620 power amp ground

ronlevandoski

I am new to this group and I have a question about a Polk product. I have a set of Polk SDA-2 speakers and a Nakamichi System One with the 620 amplifier. I need to speak to somebody who has installed one of these systems. I can't seem to find any information concerning the common ground issue that is a clear warning with the SDA-2s. Can anyone out there help me with some information?

george daniel

if you have vom you can check it by measuring between the negative binding posts,,if they are CG your reading should be zero
or close
http://www.polkaudio.com/forums/showthread.php?t=80063&highlight=common+ground+test

Tower Boss

Hello Ron,

You are good to go, and as George stated, that is the catchall way to check for a Common Ground Amp.

I happen to have a Nakamichi System-One myself that I ran a pair of Polk SDA-1A's on for awhile. Below is a Schematic of your amp.



Regards,
Mike

ben62670

Welcome to Club Polk.
Ben

PoweredByDodge

The fellow who made the "Dreadnaught", as he calls it, is on the right track. Simply 'bonding negative terminals' is not the same as 'bonding chassis ground' -- these are two completely different exercises. The negative terminal of an amplifier is a 'signal ground' or 'analog ground', as opposed to a current sinking earth ground. They are intentionally represented differently in drawings... one with the typical horizontal hash marks, the other with an inverted triangle. Depending on the design, signal ground may be bonded to earth ground, or it may not. If it is, then you can usually get away with also bonding it to another signal ground (assuming the 2nd one is also bonded to earth ground on its unit as well)... oh wait... (yes, I'm being sardonic)... if signal ground and earth ground are bonded on amplifier #1, and they're also bonded on amplifier #2, and you plug both amplifiers into the same power source, then they're now bonded via the ground plane, as they should be. Adding a jumper simply creates the ability to generate a ground loop (noise). On the other hand, if signal ground and earth ground are not bonded, then it is not kosher to bond two signal grounds together (even between channels on the same amplifier) if the channels or amplifiers were not designed to be strapped ('strap-able')

An isolation transformer is the solution.