Insulation between case and RCA jacks

[deniss77]

I'm going to customize my Onkyo A-RV401 integrated amp to include pre-outs and main-ins, so that I could use it as a stand-alone amp.

My question is - is there any reason for insulating RCA jacks from the chassis? The factory jacks (all analog signal) have a plastic buffer between RCA jacks and case, but I was going to buy standard RCA jacks with an all-metal jacket (like PartsExpress sells), so they would bolt to the chassis sheet metal.

Since the ground for RCA jacks should be same as common ground, I figured there's probably no need for insulating the jacks from chassis, but I wanted to ask just so make absolutely certain.

[jcx]

if the manufacturer insulated I expect there were ground loop noise/hum issues and would expect you should use insulated jacks as well

[stoc005]

Parts Express has some reasonably priced insulated RCA chassis mount jacks. Around 6.50 USD per pair.

[deniss77]

Originally Posted by jcx

if the manufacturer insulated I expect there were ground loop noise/hum issues and would expect you should use insulated jacks as well

I betcha they insulated for ease/cost of manufacture. The jacks look like they are molded to a large plastic plate as a large cluster, which was probably easier for assembly purposes, and then the plastic plate is mounted to chassis instead of each jack individually. So it's difficult to say whether they insulated because it's better for sound or because it's better for cost.

I'll go ahead and use insulated jacks then, just to be on the safe side.

Can anyone suggest a good way to connect pre-outs to main-ins if they need to be shorted for default operation? I've seen "linking plugs" used in amps that come with built-in pre-outs and main-ins - are those available commercially, or would I just use extra-short RCA cables?

[fastbike1]

You can just use a short piece of #8 solid copper wire. Fits the RCA just about perfectly.

[jaycee]

They are insulated from the chassis to avoid ground loop problems. If you dont do this with your replacement jacks, then it is highly likely that your amp will have hum.

[jean-paul]

Originally Posted by jaycee

They are insulated from the chassis to avoid ground loop problems. If you dont do this with your replacement jacks, then it is highly likely that your amp will have hum.

Exactly. It is better to have case ground and audio ground separated but for only one point in the case.


A little OT: despite being done less optimal than possible in a lot of gear by connecting them simply directly together there is a better old fashioned method when one cares for audio quality:

If you connect audio ground to case/safety ground ( the one where the wall outlet "earth" is connected to the casing of the amp ) with a 100 Ohm 1 W resistor paralleled with 22 nF 250 V ceramic cap you will have "isolated" and at the same time "connected" the audio ground that you want to keep clean with the safety ground that you need for safety... No injection of rubbish into audio circuits possible from safety earth/ground....No hum....Still RF protected.....Still safe....No ground loop....

[deniss77]

Originally Posted by jean-paul

Exactly. It is better to have case ground and audio ground separated but for only one point in the case.


A little OT: despite being done less optimal than possible in a lot of gear by connecting them simply directly together there is a better old fashioned method when one cares for audio quality:

If you connect audio ground to case/safety ground ( the one where the wall outlet "earth" is connected to the casing of the amp ) with a 100 Ohm 1 W resistor paralleled with 22 nF 250 V ceramic cap you will have "isolated" and at the same time "connected" the audio ground that you want to keep clean with the safety ground that you need for safety... No injection of rubbish into audio circuits possible from safety earth/ground....No hum....Still RF protected.....Still safe....No ground loop....

This is very useful info - thank you for posting this. Now it makes sense why in my vintage Kenwood amp all RCA-jack grounds have those ceramic caps on them before going to case ground.

I purchased insulated RCA jacks based on all the input here.

Somewhat OT... For connecting wire inside the amp where I need to make splices and runs to the RCA jacks and back, I am going to use solid-core wire... Should it be something like 18 or 20 AWG?

[kevvywevvywoo]

I agree, you may get an annoying ground-loop hum as you will be grounding the rca inputs at the pcb and also at the chassis. Insulated RCA inlets are cheap enough.

[nigelwright7557]

It depends on your source.
If it is not connected to earth then you really need the amp input earthing.

If the source is earthed then you dont need the input to the power earthed as it iwill likely cause hum.

As I connect all sorts to my amps I have a switched earth on the input to my amplifiers.