To ground or not to ground..that is the question! Newb has a Mac MX110 question!

TerrapinFlyr

TerrapinFlyr

Member
Hi All,
I am a complete new comer to 'getting under the hood' of vintage electronics and have a (most likely) very easy question on a preamp on which I am replacing the RCA jacks. I thank you for helping me out in this endeavor!

The unit I am working on is a Mac MX110. The RCA jacks are pretty worn and I am replacing them. If you are familiar with this unit, the original RCA jacks are kind of 'riveted' in and flared on the inside of the metal chassis wall.
I've drilled those out cleanly (Mac purists spare me please, lol) and am going to use new gold plated jacks that feature grounding rings.

The question:
I know that the 'input' jacks will need grounds added.
Do the output jacks ('MAIN') on the MX110 to the power amp also need grounding added or is this unnecessary?
I've actually wired the MAIN output jacks with and without grounding and they perform the fine either way, no buzzing. Although, I don't want to pass anything to my amp that should have been grounded at the preamp. I also don't want to crowd the preamp with unnecessary ground wires (it's tight in the mx110 chassis already)

Perhaps someone could shed light on the proper grounding needed (or not) on the MX110 outputs?

Thanks!
 
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You should be good to go. The only other grounding issue maybe from TT to amp and amp to preamp grounds. (If necessary at all).

(hate you tube guys with green envy when I see that class of gear)
 
If the originals were grounded to the chassis at the jack, then the replacements should be as well. If the originals were isolated with a ground lead going back to a central ground point or a floating ground on a preamp board (some signal grounds will be isolated from actual ground with something like a 3 ohm resistor), then the replacements should be wired the same. Changing the ground connections can lead to serious hum problems that can be very difficult to solve.
 
fred soop said:
If the originals were grounded to the chassis at the jack, then the replacements should be as well.
Click to expand...
The original jacks were all metal directly into the metal wall of the chassis. No grounding wires on the original jacks. The non-original replacement jacks have a grounding tab, unlike the originals.

So, I cannot visually detect the original grounding that may (or may not) have been occurring..

I've added ground wires to all of the 'input' jacks.
I did not add a ground wire to the 'output' jack and it is working clearly. Just want to know if that is 'okay'.
 
Best thing to do at this point is test it. If there is no hum, great. Otherwise, you may need to change the grounding architecture.
 
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