Grounding in amplifier internal wiring

[sdk]

Hi,

I've now reached assembly stage in my project

In the process of soldering and connecting various parts like the input RCA sockets to the input selector switch, I'm getting conflicting advice.

Some articles suggest that the ground wire should loop from the ground pin of the RCA sockets to the input side of the preamp, then from the output side of preamp to input side of power amp

My friend who is helping me with advice is suggesting that the ground wire from the RCA sockets, for which I'm using the shield of the cable, should be connected only at the RCA sockets and left hanging free at the other end at the selector switch. This way only the signal wires will be connected from selector to the preamp input and no ground.

How is one actually supposed to wire an amp?

Regards

 

[keith_correa]

Excellent information here:

Ground Loops

<p>Updated with new material 7th January 2019 This set of c. 70 slides is the culmination of my experience over a period of about 25 years building numerous power amplifiers and preamplifiers. I first started out in audio around 1975 or 76 as a teenager. Some of my creations were reasonably...

hifisonix.com

 

[saikatbiswas82]

One of the best article for grounding (or avoiding ground loops) -

Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

Earthing (Grounding) Your Hi-Fi. Detailed explanations of the safety and sonic aspects of proper earthing (grounding) techniques

sound-au.com

For directional RCA (like audioquest), you need to use multistranded dual core (twisted preferred) shielded mic cable.

At source - Red core connected to center pin. Cable's outer shield and black core connected to outer ring of rca.

At destination - Red core connected to center pin. Black core connected to outer ring of rca. Cable shield is not connected at destination.

 

[keith_correa]

Some articles suggest that the ground wire should loop from the ground pin of the RCA sockets to the input side of the preamp, then from the output side of preamp to input side of power amp

My friend who is helping me with advice is suggesting that the ground wire from the RCA sockets, for which I'm using the shield of the cable, should be connected only at the RCA sockets and left hanging free at the other end at the selector switch. This way only the signal wires will be connected from selector to the preamp input and no ground.

I’m assuming that your question is specifically pertaining to RCA->selector->Pre in.
You say you are using a single cored shielded cable and you’re using the single core as the signal and shield as the return/ground.

option 1 - you loop the single signal core(s) [from multiple RCA’s] to the selector and connect the grounds straight to pre in. After the switching, a single signal core loops back to the pre in. If this were done, you’d be stripping off the shield partway to connect straight to the pre in, right? Why use a shielded cable then? You’re losing benefit.

option 2 - you loop the whole cable(s) to the selector and after the selector, one cable back to pre in. Here the multiple input grounds will connect to the ground wire cable post the selector.

I don’t understand what your friend says about leaving the ground open at the selector end. How will the loop be complete? You need to speak to him again to understand clearly what he’s suggesting.

 

[sdk]

I'm using 2 core shielded cable per RCA pair input socket for left and right channels

I've tied the shields together of both the wires and soldered it to the ground pins as common ground

At the other end I've connected the cores to the respective selector switches. The common tied together grounded shield at the selector end was my query.

Since he is traveling, I'm unable to contact him till he reaches back home, so I put up my query here

In the meantime, An article on Rod Elliott's site, I think but may be somewhere else, mentions something similar. Where you use 3 core wire and not 2 core. On the rca side 2 cores connect to left and right. The third core and Sheild is connected to the ground

On the selector side or preamp side only the 3 cores go into input as LGR and the Sheild is not connected. Hence it is connected only at one end.

So I my case this may not work as I have only two cores for L and R and I will have to connect the Sheild ground to preamp to complete the loop

 

[sdk]

One of the best article for grounding (or avoiding ground loops) -

Earthing (Grounding) Your Hi-Fi - Tricks and Techniques

Earthing (Grounding) Your Hi-Fi. Detailed explanations of the safety and sonic aspects of proper earthing (grounding) techniques

sound-au.com

For directional RCA (like audioquest), you need to use multistranded dual core (twisted preferred) shielded mic cable.

At source - Red core connected to center pin. Cable's outer shield and black core connected to outer ring of rca.

At destination - Red core connected to center pin. Black core connected to outer ring of rca. Cable shield is not connected at destination.

Oopsies!

Should have read my own thread in full before replying to Keith!

So Rod Elliot it is where I read it

 

[superczar]

Hi,

I've now reached assembly stage in my project

In the process of soldering and connecting various parts like the input RCA sockets to the input selector switch, I'm getting conflicting advice.

Some articles suggest that the ground wire should loop from the ground pin of the RCA sockets to the input side of the preamp, then from the output side of preamp to input side of power amp

My friend who is helping me with advice is suggesting that the ground wire from the RCA sockets, for which I'm using the shield of the cable, should be connected only at the RCA sockets and left hanging free at the other end at the selector switch. This way only the signal wires will be connected from selector to the preamp input and no ground.

How is one actually supposed to wire an amp?

Regards

The ground wire from the RCA socket most certainly needs to go to the ground of the amp - I am not sure if I am missing something here

Your question if i understand correctly pertains to the line level input RCA. Your L/R signal is at a differential to the ground on the source side say +/- 1V against the source ground
Your amp input needs the same differential which it won’t get if you leave the RCA input ground open.

Avoiding ground loops is a different issue and something you need to worry about after at the minimum completing the circuit.
If you leave your RCA ground open, your circuit isn’t even complete

On a side note, The link above is for avoiding ground loops on the mains side

 

[kaushik]

Along with grounding u can decouple the pre with 820e resistor in positive in case the v+ is coming from power amp side .


V+Capacitor to ground ->>820E-->Pre amp Positive(add 330uf) grounding capacitor

Decoupling helps reduce hum in a big way