Dedicated 20 amp lines/should i use a sub panel

noromance
906 posts 01-04-2018 11:20pm

Looks like I should expedite my plan to rewire the power cords on the power amps with new OFC cables including connecting the safety ground. I’ve been meaning to do it after changing the power cord on the preamp with very positive results. Thank you.

@ noromance,

Is this the schematic wiring diagram for your amps?
http://www.freeinfosociety.com/electronics/schematics/audio/pictures/eicohf22.gif

If so, see that C13 (.03 600V) cap connected to the AC line that is connected to the chassis? (Just to the right of the AC line fuse). That would have to be removed before connecting an equipment ground wire to the chassis.

That’s the cap I was attempting to ask Al about in my previous post. I forgot it was/is referred to as a "death cap". (Thanks imhififan for the 2 Links above.)
I always wondered why the cap was installed on the fuse AC line and not on the non fused line. With the old original non polarized plug the user had a 50/50 chance of plugging the plug into the wall outlet and getting the neutral, (The Grounded Conductor), the line the cap is connected to. Again note the fuse would be connected to the neutral line.
I guess back in those days electrical safety was seen different than it was in later years.
One example, old Knob and Tube wiring the HOT was ran directly to the ceiling light and the neutral ran through the switch on the wall.


The amps, at the time they were designed and built, were not designed to be directly connected to an equipment ground. You will be connecting the amplifier’s circuit ground/signal ground directly to the mains safety equipment ground. I am not sure if that will improve the SQ of the amps or harm it. Someone like Al or Ralph would need to chime in with their thoughts.

Jim

Thanks for your thoughts and questions, Jim.  Generally speaking a direct connection between AC safety ground and signal/circuit ground is an invitation to ground loop issues (both hum and high frequency buzz).  In good modern designs the two grounds are often connected to each other through a resistor having a resistance in the area of 10 to 100 ohms, which would probably be impractical to do in this case since chassis is used as signal/circuit ground in many places.  It would also stand a good chance of being sonically undesirable, due to the small impedances it might create between grounds at different circuit points within the amp.  So I would recommend that Noromance leave well enough alone, and if he chooses to upgrade the power cords on the amps that he **not** connect AC safety ground within them.

Also, regarding the "death cap" (and thanks to Imhififan for providing the good reference), it's worth noting in the photo of the underside of Nomance's amp that the cap has been replaced with a modern one.  So presumably leakage within that cap is not an issue.

But it doesn’t [hum] when I add my REL sub.

Noromance, what model is the sub, and if you are using the high-level Speakon connection what is the black wire connected to?

Also, if you want to pursue the hum issue further what you might try would be connecting each amp to its own dedicated line, with the two lines on the same AC leg, and then trying all four combinations of the orientations of their AC plugs. If the plugs are polarized or are 3-prong types, even though the safety ground is not used within the amps, for experimental purposes you could try that using cheater plugs.

Regards,
-- Al

@noromance

If you can’t solve your problems with breaker assignments, etc., for whatever reason, consider an isolation transformer. The added benefit is over-voltage protection from an electrical disturbance such as a lightening strike or a transformer event.

Of course, this comes at a cost. First, they hum while they work, so they must be sited outside a music room. Second, some electrical inspectors don’t understand, and get tense or weird. Third, they aren’t cheap. But they do work. I have one in front of everything which produces signal: ESL power, amplifier power. I also isolate motor controllers, but that’s just silly old me.

A separate ground was mentioned above, but I would be wary of that option unless you have a dedicated subpanel to which ALL the audio is connected, and it will always be that way. Otherwise you invite a ground loop of heroic proportions. Typically the ground plate is supported by fresh water copper pipe, which does a great job (assuming a moist environment around the pipe, and of course, unless you have plastic!!!).

Plitron sells good transformers, bare and boxed, and they sell directly to the public.

Al (almarg),

Thanks for responding to my above post. I was thinking the same things as you stated in your last post. And no doubt circuit grounds/signal grounds are more than likely connected to the chassis at various places.

Would you leave the cap where it is now located on the same AC line as the fuse? For proper operation the cap should be connected to the neutral conductor. Problem with the way it is now the neutral is fused. (I remember reading somewhere the user should reverse the 2 wire plug in the wall outlet for what sounded the best with the least, buzz/hum/noise.)

I think for a test I would first lift the cap from the chassis and then check for the proper, correct, AC polarity orientation for the primary winding of the power transformer. That will determine which lead of the primary winding should be connected to the Hot conductor and which lead of the winding should be connected to the neutral conductor. Hopefully the AC line that is fused will be the Hot. There’s 50/50 chance. I doubt back when the amps were built anybody back then checked.
At any rate if possible I would want the fuse on the Hot mains conductor and the cap connected to the mains neutral conductor to chassis ground. I would check and wire both amps the same. (Of course for many years the plug for the amps were a 2 wire non polarized plug that had a 50/50 chance of the fuse being fed from the mains Hot conductor.)

Al, what do you think?

Jim

Thanks @almarg. Yeah, I'll try it with and without the safety ground and see what sounds better. Thanks for your vote of confidence in the amps' wiring! The Speakon black goes to the right speaker ground IIRC. Not sure I'll bother with the second run. It's fine and juicy as it is and I've other fish to fry (like a new idler wheel from AF for my 401!)