Head cab shielding

[Blooze]

I’ve built a head cab for my Gibson Ga-18T clone. The amp was built in a JTM45 aluminum chassis. I was wondering if I need to put some sort of aluminum shielding between the chassis and the wood cabinet?  I have a piece of aluminum flashing cut where it goes the entire length of the chassis and sits just inside the front/rear panels. If I make it as wide as the chassis you can see the sheeting because the rivnuts keep the chassis slightly up off the cabinet. Not sure if this will work or even how to attach it flat.

[kagliostro]

Usually that is unnecessary

The max thing to which you can think (to me) is to cut the aluminium sheet to be used as a bottom closure of the chassis (it must also be connected electrically to the chassis)

Franco

[Blooze]

I ended up using some Nashua aluminum tape I had instead. Folded the ends over so the aluminum foil actually touched and drove a staple across each piece. Got continuity from the tape to the transformer bell ends so I think I’m good.

[HotBluePlates]

... If I make it as wide as the chassis you can see the sheeting because the rivnuts keep the chassis slightly up off the cabinet. Not sure if this will work or even how to attach it flat.

You could make that sheet wider/larger than the chassis opening, then the rivnuts won't matter.

But since you already tried something, did you hear a noise-difference?  Sometimes we chase this stuff that wasn't needed.

[Blooze]

... If I make it as wide as the chassis you can see the sheeting because the rivnuts keep the chassis slightly up off the cabinet. Not sure if this will work or even how to attach it flat.

You could make that sheet wider/larger than the chassis opening, then the rivnuts won't matter.

But since you already tried something, did you hear a noise-difference?  Sometimes we chase this stuff that wasn't needed.

Nope. No difference, but I figured it couldn't hurt.

The issue with the sheet was that I could get the rivnuts to contact fine on the ends of the chassis, but the rivnuts made the chassis sit slightly up off the cabinet with a small gap at the front and rear panels.  So if I tried to make the sheet as deep as the chassis (front to back) you could see the slightly wavy edge of the sheet. Mainly it just looked terrible and would have looked worse with staples on the edge to try and hold it flat.

[sluckey]

Try countersinking the mounting holes so the rivnuts sit down in the countersinks. This will allow the entire chassis to fit flat on the bottom of the cab and press the shielding sheet between the chassis and bottom of the cab.

Alternately, use aluminum duct tape rather than a sheet of flashing.

[acheld]

Try countersinking the mounting holes so the rivnuts sit down in the countersinks.

Usual countersink bits don't work well for this application.  You need a flat bottomed countersink (eg, something like a Forstner bit, or a flat bottom mill bit).  I have done this, but it's not easy, even with a good drill press and using (expensive) low profile rivnuts.

Alternately, use aluminum duct tape rather than a sheet of flashing.

This works great!  Simple, elegant.

To be honest, I haven't shielded my guitar amp builds in a long time.   I have not seen the benefit -- though I am sure there are situations where it would be.

[sluckey]

You need a flat bottomed countersink (eg, something like a Forstner bit, or a flat bottom mill bit).

15 minutes with a hammer and chisel.   

[AlNewman]

Aluminum duct tape works great, I've used it, and just used the sharp point of my multimeter probe to pock holes into the seams to get continuity.  It also made a big difference on my amp when in relation to wifi routers, etc.  That was the reason I used it, as I was getting direct interference because my amp was sitting by my router.  I never used rivnuts, but speednuts, which slide over the edge of the chassis.  I then sanded the contacting surface, which created good continuity, but there still is a slight gap between the chassis and cabinet.