[Jaypee]

Hey guys, it's been a qhile since I posted here - been busy building a motorcycle for the past year.
 
A friend dropped his vintage Harman Kardon 330c stereo solid state reciever and asked me if I could modernize the thing a bit. What he was most concerned about was that the powercord does not have a groundpole (he thinks that in case of a shortcut, the ground will go through the chassis and anyone who's touching it). He also told me there was a lot of humming/static noise coming from the reciever during listening and he thought that adding a proper ground might aid.
 
What do you guys think?
- Is there a point in taking the old 2-wire powercord out and replacing it with a 3-wire one?
- Can I reduce the static noise somehow?
 
EDIT: here's a service manual for the thing:
http://akdatabase.org/AKview/albums/userpics/10004/Harman%20Kardon%20330c%20Service.pdf

 

[HiGHFLYiN9]

Most older equipment came with non-polarized power cords, which isn't quite as safe as three prong plug with ground connection for the reason your friend mentioned. That being said, most older equipment makes use of the chassis as the circuit ground. If you are dumping the circuit ground into the safety ground and have another piece of equipment that's doing the same thing, you can end up with a lot more noise. 
 
I think it's unlikely that adding a 3 prong power cord would solve your noise issues, there's likely something going wrong within the receiver that needs to be remedied with a bit of troubleshooting, which really should be turned over to an expert due to the voltages within the unit. 

 

[Uncle Erik]

A 3-prong plug is a good upgrade.  I don't know if the chassis is hot (being used as ground) in that unit, but I think the ground should be connected to the cabinet.  That way, if something shorted between the chassis and cabinet, it'd go to ground instead of through a person touching it and to ground.  (If I'm wrong, someone please correct me.  This stuff is important.)
 
The humming and static are likely due to old electrolytic filter capacitors in the power supply.  I'd put new ones in.  Not terribly hard or expensive, but be sure to discharge the old ones before touching them.  You might also want to shoot some ProGold or other cleaner into the pots.  They get dry and scratchy after awhile.
 
 

 

[Jaypee]

Okay, if you'll look at the service manual link I posted before, on page 11 it shows the wiring diagram for the power cord. There's a resistor R8, which connects the power cord to the chassis. There's also a metal screwable stud on the rear panel of the reciever with the text GND above it.
 
Should I just attatch the third prong straight to the chassis and leave the R8 in place? What is the function of the R8 anyway?

 

[jamesbobo007]

Yep, attach the ground line to the chassis, if there is a stud there already I'd use it.
Leave R8 alone. unless your going to swap out the accessory receptacle for a 3 prong or remove it entirely.
But, with out being insulting, that diagram is pretty clear and if your questioning things, you probably should leave it alone.
If your in doubt; dont do it. Ask more questions