Toroidal transformer bolt question & mobile phone interference

[markiemrboo]

I have nearly finished putting my amp in a case now. I didn't know how to mount the LED on the front panel really, so I just cut that off for now. I can hear the soft start relay click on and off anyway.

I also have no stand off feet for the bottom yet, and I was just wondering if it is safe to let the bottom transformer bolt touch anything metal?

I know you can't let the top *and* bottom of the bolt touch the case at the same time, but is there anything wrong with letting just the bottom touch another piece of metal e.g sitting on top of my current amplifier?

EDIT: Also, I seem to get mobile phone interference coming out of the speakers connected to the GC. Could this just be the lack of ~100nf? capacitor on the disconnecting network?

[v-bro]

I don't see why not, aren't toroids a completely closed electro-magnetic system?

[FastEddy]

Best advise for mounting anything with voltage potential greater than 70 VAC or 30 VDC = use insulators where possible.

The center bolt on a torrid transformer is generally a long ways away from any of the windings ... BUT ... if you can, isolate and insulate the big mounting. Plastic or fiber washers and/or rubber o-rings under the bolt head where it may meet the chassis metal usually work. There are actually plastic washers available with cute little rings for the chassis hole. You usually have to search the bins at a surplus store to find these kinds of things, but it is a good idea to try. Check with a volt/ohm meter for isolation. The rules for production manufacture of electronic devices are cryptic and very complicated, but common sence and common cents should rule these kinds of discussions.

Another good reason for insulating and isolating that big bolt with plastic or fiber washers = if the completed amp gets dropped more than a few inches, the plastic will take a lot of the momentum forces and shock and could save the day from a serious distortion or even breakage of your chassis / case.

(Many bigger torrid transformers are shipped with big rubber washers the same size as the torrid = use 'em if you got 'em for the same reasons as above ... both electric insulation and vibration / shock dampening.)

[cliffforrest]

The point is there must not be a shorted turn! This will happen if there is a completed conductive path around the torriod core - a simple way of this happening is if both ends of the bolt are connected together or grounded.

"Touching" anything is not the issue.


Just make sure that the top of the bolt and its clamping plate cannot be grounded, and/or isolate the bolt bottom from ground.

[markiemrboo]

Originally posted by v-bro
I don't see why not, aren't toroids a completely closed electro-magnetic system?

No idea

Originally posted by FastEddy
Best advise for mounting anything with voltage potential greater than 70 VAC or 30 VDC = use insulators where possible.

The center bolt on a torrid transformer is generally a long ways away from any of the windings ... BUT ... if you can, isolate and insulate the big mounting. Plastic or fiber washers and/or rubber o-rings under the bolt head where it may meet the chassis metal usually work. There are actually plastic washers available with cute little rings for the chassis hole. You usually have to search the bins at a surplus store to find these kinds of things, but it is a good idea to try. Check with a volt/ohm meter for isolation. The rules for production manufacture of electronic devices are cryptic and very complicated, but common sence and common cents should rule these kinds of discussions.

Another good reason for insulating and isolating that big bolt with plastic or fiber washers = if the completed amp gets dropped more than a few inches, the plastic will take a lot of the momentum forces and shock and could save the day from a serious distortion or even breakage of your chassis / case.

(Many bigger torrid transformers are shipped with big rubber washers the same size as the torrid = use 'em if you got 'em for the same reasons as above ... both electric insulation and vibration / shock dampening.)

Alright, thanks. My toroid is 500va, but didn't come with any rubber / plastic washers. It has some sort of foam pad for the top and bottom, but I think these might be pretty normal. I will look in to some plastic or rubber washers.

Originally posted by cliff
The point is there must not be a shorted turn! This will happen if there is a completed conductive path around the torriod core - a simple way of this happening is if both ends of the bolt are connected together or grounded.

"Touching" anything is not the issue.


Just make sure that the top of the bolt and its clamping plate cannot be grounded, and/or isolate the bolt bottom from ground.

Alright, cool Time to stick it on top of my current amp then I have just drilled some holes in the bottom for feet, but don't actually have any feet yet.

Thanks very much!

[CarlosT]

How about plastic bolts?

[v-bro]

Offcourse! Thanks Cliff, very clear answer. So you can actually measure
a voltage between the top and bottom of the bolt, funny.....

[v-bro]

Plastic bolts, hmmm Think a toriod is quickly too heavy to hold with a plastic bolt... I would rather suggest tie wraps....a couple...

[CarlosT]

OK then...how 'bout some plastic bolts and some silicone adhesive/caulk?

[v-bro]

In the same shop they'll probably sell rubber rings....