Isolating input jacks

[dude]

When isolating Switchcraft input jacks, I find the isolating fiber washers sold are not the correct size.

Don't want to enlarge the input holes, but are these washers meant to have a bigger hole?

Never could figure out the correct way to use them, I figure you use two fiber washers with the chassis between but the holes are too small.

Am I missing something here...?

al

[Willabe]

Yes, you have to make the chassis hole bigger.

They work like the insulation over a piece of wire, ie, a sleeve. The sleeve, isolation shoulder washer x2 or a isolation shoulder washer and a flat isolation washer, goes inbetween the jack's bushing and the chassis/face plate.

With a Marshall type jack (Cliff jack) the jacks bushing is plastic so no need for isolating shoulder washers.

(I'm not sour about the Cliff jacks bushing size, I don't think their drop in replacement's for switchcraft jacks.)   

[sluckey]

They are the correct size. The hole in the chassis must be 1/2" diameter. Use 2 shoulder washers per jack. You cannot isolate the typical switchcraft jack if you don't make the chassis hole 1/2" diameter.

[dude]

Thanks, kind of a dumb question as the answer is so obvious that the hole has to be enlarged. Guess I was hoping for a miracle answer  and not to have to enlarge a 3/8 inch hole, especially in a Vintage amp. Guess in that case "use a Cliff jack".

I put a lot of jacks in for the speaker of amps that are hardwired outputs, nice to able to change speakers easily. I have been using cliff jacks in this case but have a ton of those fiber washers.

Since I'm asking this question, the inputs with Switchcraft's are grounded right at the nut but to help with hum, is there any benefit of using fiber washers and grounding the input to the same place as the preamp filters...?

al

[Willabe]

the inputs with Switchcraft's are grounded right at the nut but to help with hum,

Different guys have different grounding schemes that work for them. I would say that most don't isolate the input and speaker jacks from the chassis. (I do on my few builds.)

Our host Doug and Sluckey have a lot of builds that they both have posted wonderful documentation and pictures with wonderful layouts and lead dress, study/copy them as they are proven builds. Also Tubenit has posted many proven builds with great documentation too.   

Look in here for some info on grounding;
 
http://www.valvewizard.co.uk/Grounding.html

[AZJimC]

It's my thought that isolation of inputs is almost never needed. Fender, and nearly every other mfg have had many, many years of amps that run quiet, with their jacks installed in 3/8" holes, in normal contact with the chassis. some have a second ground contact via the sleeve lug, some not. All are very quiet. As an example, I have a 70's super reverb, that had a bad hum when I got it. One of the 100ohm filament circuit balance resistors had burned open. Replacing that with a pair of new ones stopped the hum, and I've never heard a whisper of hum from it since. (The hissy Carbon comp resistors are another story)

I see guys with concern about "ground loops". I believe ground loops are a concern when they are large, like a common ground on inputs of two amps that also are grounded via power cords. That could create quite a huge antenna that picks up 60hz in walls around it. A loop of a few inches inside a chassis has never been an issue for me. Several feet of cords are a large antenna, and a low value resistance as well.

I have had to isolate a few jacks, where I've replaced marshall type jacks with switchcraft. Possibly, it was not needed in most of those cases, but I was attempting to copy the original hookup. I have amps that are point to point, with each terminal strip providing it's own lug for grounding of that stage, or using a center post of the sockets as a grounding point, with a wire running from there to any convenient chassis solder point, or a screw. These amps are also very quiet unless something else is wrong. Fenders very likely didn't have a hum from the factory, and I've never seen factory isolated jacks in one.

Just my two cents,
Jim

[Willabe]

I copied and moved moved AZJimc's post to the link below;

http://el34world.com/Forum/index.php?topic=18828.0

Please continue this threads topic there, thank you.


                             Brad