Question for rewiring the C20's power cable

[grantray]

A previous owner replaced the original Belden with a Taiwanese cable that needs to go, too. I've got a 16g Qualtek prepped and ready to go, but the schematic doesn't list which terminal should get the live wire. Is there a preference for which terminals should get the hot and neutral lines? Looking at the schematic and the preamp's layout, my gut tells me the live gets soldered to the top terminal. Is that right?

 

[c_dk]

The hot should precede to the power switch and fuse. You will need to trace as your posted picture does not include them.

 

[grantray]

The hot should precede to the power switch and fuse. You will need to trace as your posted picture does not include them.

Thanks for the help, c_dk. That'd be the top, then. Those two brown wires on the first two ac receptacles are out to switch, followed on the third receptacle's black/white to fuse.

 

[damacman]

Keep in mind that this unit would’ve originally included a non-polarized cord.

 

[grantray]

Keep in mind that this unit would’ve originally included a non-polarized cord.

Yep! However, all the plugs in my house are polarized.

 

[MACKIE1975]

The original cable (plug) can use either way. Is it really matter?

 

[damacman]

The original cable (plug) can use either way. Is it really matter?

My point exactly. The design of the C20 was done 20yrs before polarized plugs were used for CE.

 

[clinic-audio]

Hello

What is the problem with a non polarized plug to be connected to polarized socket ??
If you don't know if you power cord is correctly connected , you can make easy check :
1) do not connect anything to your C20 (output and input)
2) plug the C20 power cord to the mains
3) switch the power on with C20
4) make a AC V measurement between the ground of the chassis with any of your AC input cable . Take note of the value (ACV)
5) make the same measurement between the chassis but with the other wire of your AC input cable . Take note of this value too (ACV)
6) one value should be much more high than the other one and then, you know which one should be polarized

with this method you don't need to touch anything (no solder )

 

[grantray]

My point exactly. The design of the C20 was done 20yrs before polarized plugs were used for CE.

And that difference in eras for power delivery in the home is why I'm asking/verifying if one terminal is better than another when moving to a polarized plug. Because if the older circuits designed for non-polar AC flowing into both terminals (like all older power supplies) have shown over time to like polarized AC delivered a certain way, I'd want to make sure I solder up the new cable accordingly.

It may seem silly, but I've learned weirdo stuff like this is common in old cars, motorcycles, and cameras as the specified lubricants, batteries, etc., were phased out and replaced over the decades.

 

[whoaru99]

Just to be clear, the AC itself isn't any different coming from polarized or non-polarized receptacle. The difference is that the polarized receptacle drives a common relationship of connection to hot and "neutral" whereas, with non-polarized, that relationship was arbitrary depending on which way you plugged in the cord.

Anyway, what I think clinic-audio describes is basically the direction to follow. Connect the wires one way, measure the C20 chassis to ground (or neutral if there is no safety ground) then connect the wires the other way and remeasure. Connect which way gives the lowest voltage reading chassis to ground.

I have a couple older pieces with non-polarized cords. I made this type of measurement then marked the side of the plug to indicate which side goes to hot terminal (the narrow slot of the receptacle. I remember by "short slot hot").

 

[c_dk]

I would think that the fuse would precede the power switch and the transformer primary winding......especially the transformer if the enamel insulation would break down but according to the schematic the fuse is between the two but with switched convience outlets that is not possible.

 

[grantray]

I would think that the fuse would precede the power switch...

That's what I thought as well. I get the placement of the hot outlet before the fuse and switch, but the rest of the layout is all kinds of wonky with the fuse being connected to a middle outlet. However, I know the circuit works properly because I popped the fuse when swapping in the LED replacement bulbs last month. Ha. My guess is that placement of the fuse is less critical due to the alternating current, but that's just wild speculation, at best.

FYI, I've now got the C20 hooked up with the new power cable and currently playing via the MR67. Low level hum through the Valencias when powering on the Asano 2A3 amp (which is powered through the C20) went down a good notch or two, and overall clarity during playback is definitely up a tick. Pretty darn good for non-"audiophile" Qualtek 16 AWG cable using an industrial Hubbel AC plug.

I also just secured a MR-55A locally with a very clean chassis to go along with the C20, (I love the MR67, but I also miss the weird stuff that pops up on AM) and will probably have all kinds of new silly electronics questions within the next week or so about McIntosh's early FM/AM tuner