Insolated input jack?

[Madison]

I just found that the Plexi type build I am working on is requiring me to have an isolated input jack (grrrrrrr, me dislike cliff jack and have no washer for switchcraft....grrrr)

Anyway,anybody know when and why this happens?
First time for everything.

[phsyconoodler]

You can use switchcraft for your plexi build.Not a problem.You don't need cliff jacks if they confuse you.

[stingray_65]

It is my understanding that the logic behind cliff jacks is that a chassis is not a reliable enough connecton for the input ground.

using any lead off the ground lug of a switchcraft style jack will imediatly cause a ground loop even if it is un-noticable. that lug can however be a good place to ground a component, but it will have the same potential for spotty  grounding.

That said, I prefer the switchcraft style myself. I've found guitarist like to trip on thier cords and break cliff style jacks.

The switch craft jacks can be assembled to the chassis to provide an improved grounding, the use of serrated washers is a must IMHO along with a fresh scratch of steel wool on the mounting surfaces.

Put the serrated washer on the backside where it wont be seen. a TINY drop of removable loctite on the nut will also keep things tite for a while.

[HotBluePlates]

Well, I don't know what specifically is causing you to need an isolated jack.

With amps, there's "theoretically correct" and "good in practice". Sometimes things that are technically wrong work just fine. Sometimes what is technically wrong is halfway between 2 approaches that would each be technically right, but is missing some minor detail.

I think jacks are one of those things where you can get away with less than perfect in 98% of cases, but those other 2% will simply not settle for less than perfect. Usually there is some additional factor at play.

It is my understanding that the logic behind cliff jacks is that a chassis is not a reliable enough connecton for the input ground.

I think the chassis is plenty reliable for a ground connection, unless there is oxidation between the chassis and the ground connection.

The real problem is that ground is not a magic place where signal disappears, but is simply a common point for various circuits. If you mix a small, clean return current for your input signal with a large, noisy power supply return current, then you hear hum/buzz along with your intended signal. The end goal of every grounding scheme, whether simple or rediculous, is to create a solid return path for various currents without unwanted mixing.

[Madison]

It's weird, I have no idea what is making it like this either.
I have been following Hoffman's ground scheme.
When I use a cliff jack, I ground the jack plus the preamp ground to the back of the pot ground bus and everything is happy.
As soon as I use a s-craft all hell break loose; it's like the shielded wire from the s-craft jack to the input grid isn't shielded at all.
I usually just ground the preamp and shielded wire ground to the back of the s-craft jack ground lug, bolt to chassis and be done.
I will check over my ground points again.

[sluckey]

Can you post a hi rez pic?

[Madison]

A mess as of now.This is the prototype.
Lot of spare parts being used up.(hence the pots with resistors strapped on.....no crude jokes please)
Preamp ground and jack disconnected in the pic.
Yes, it is the circuit you think it is.Board layout to be posted as soon as it is tested.
OT-Edcor CXPP50-MS-6.6K
Choke-from a 36 watt that never came to be.
Bright switch not bolted in.
BTW, it has some crazy over the top ......I'd say "modern" OD when pushed.

http://www.funkydolphins.com/HTW

[sluckey]

Can you post a pic that shows the offending switchcraft jack wiring?

[Madison]

I'd have to reinstall it.
I hooked the preamp ground and the shield ground to where the 1M terminates on the 12A pic here.(not the 68K and 1M joint)
http://www.el34world.com/charts/CommonHookups.htm