Pitctorial about using shielded wire

[cab42]

John,

Thanks for all your work.

A very useful article.

I have a JFet Vulcan that needs shielding very badly.

Regards

Carsten

[John Lyons]

The box material whether steel of Aluminum isn't much of a concern for low voltage pedals. With amps it plays a part sometimes...
Shielding is not always about keeping things outside the box out of your ciruit. Sometimes you need to keep things inside the box separate and from others and sometimes shielded. The input and output wires should always be separated by the most distance you have to work with. ANd short as possible.
95% of the time if you shield the input lead from the jack to the switch and then to the board you will be fine. Then possibly the output jack leads if you want to go further.
John

[idlechatterbox]

Shouldn't it be irrelevant how long the leads are IF they are shielded properly? Or am I missing something? 

[John Lyons]

Well it depends how you look at it. If you have short leads you may not benefit form shielding. But if you have long shielded leads it shouldn't make too much difference how long they are within reason. Shielding anything less than a couple inches long (assuming it's not too close to anything which will make it osciallate is not going to do too much.

It's better to solve the problems before putting on "band-aids". There a many high gain builds with no shielded wire. But the layout of the board and the pots has to be very strictly followed. With a small box often times this is hard to do, although short wires are good!

Some things to watch out for:
Keeping the input jack lead away from the output jack leads. They get close at the switch of course but as much as you can sepatarte them elsewhere the better. What is happening is that with enough gain you will create a feedback loop and you will get some squeal (or possibly even worse as you can't  completely hear it) it will effect the frequency responce and you may not notice that it's happening. The higher the gain the more this become crucial.
Wires from gain controls, volume and to a smaller extent tone controls should be laid out so wires are short and not parallel and running along  high gain wires such as volume and gain controls. It's a bit confusing but basically keeping things neat will go a long way.

Laying out the circuit so the input  is on on side and the board lays out from on side to the other is a good way to go. This way the controls are in order somewhat and don't cross over each other. Wiring straight  from the pad to the pot neatly.
When wires leave the board they become antennas for noise and oscialtion.

John