Shielded Wire for Outboard Inputs?

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OK Gents. I'm scratch building and a bit green at layout and theory.

Working on a Marshall 18 watt clone using a radio chassis. The input jacks (4) will be mounted to the wooden radio cabinet, and so I'll have to run a harness from the jacks to the chassis.

I'm planning to use a 5-pin DIN plug on the chassis for easy removal if/when needed. To that end, I was planning to use a 4-conductor shielded cable for the harness run, with shared ground for all 4 plugs earthed via the shield to my bus bar through the DIN ground.

What am I missing? I know there are lots of different theories on input/output jack ground isolation. This doesn't need to be a zero-hum jobber.

Mike
 
I am not a fan of adding more connectors in series with sensitive inputs. If I had to pull the chassis, I would just take the nuts off the jacks and let them dangle on their wires.

I see no reason why the four input jacks cannot share a ground. trouble arises when input jacks share a ground with something else, like a filter cap.
 
IMO a guitar signal isn't particularly sensitive, since it may be a hundred to a thousand times bigger than, say, a typical 1 mV signal from a cassette tape head (remember those?). Even though the guitar signal is from a high impedance source, I would say it's big enough that a DIN plug in series is very unlikely to cause any audible degradation.

I agree with Enzo about the shared ground (for multiple inputs) not being an issue.

The question in my mind is: how likely is it that three of those four inputs will ever actually be used? I think this input design dates from the days when there was no sound reinforcement system, and everybody plugged into the one guitar amp that was all the entire band could afford.

Today, I can see one high-sensitivity and one lower-sensitivity input, maybe, in case someone uses a guitar with active pickups or other extremely high output. But four inputs? If it were me, I would be tempted to turn one of them into a channel-select footswitch jack, and a second into an LED channel-select indicator light. Then mod your 18-watter a bit to have two "channels", for example, lotsa gain and even more gain, or clean and crunch, etc.

Good luck with the project!

-Gnobuddy
 
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