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Old 13th September 2011, 02:26 AM   #21
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Ah...sounds like a good idea, only problem is: I only need like 3 feet of it. =D
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Old 13th September 2011, 03:11 AM   #22
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Any broadcast engineer would probably give it to you. My own stock is on the other end of the state or I would. I think others here might if you offered to cover postage.
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Old 13th September 2011, 03:35 AM   #23
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Originally Posted by gootee View Post
I'm curious about why grounding the shield at the tube-input end would be better than at the chassis end. I know why it would definitely be better if using unshielded twisted pair. But would it also be better for just the one-end-only ground of the shield of a shielded pair?
I'm probably being a heretic here but I typically float the connectors from the chassis so have to connect both ends of the shield. Using the chassis as a conductor is a fine way to create ground loops.

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Old 13th September 2011, 03:54 AM   #24
benb is offline benb  United States
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It sounds like you've already got your mechanical layout done and are running the wires back and forth/front and back through the chassis, but there are ways to substantially shorten the signal path. Selector switches on the front could operate relays in the back instead of switching the signals directly. Volume control potentiometers can be in the back, operated by long shafts that come through the front panel (and of course rotary selector switches can be controlled this way too). I recall Heathkit ham radios (SB 300/400 series) doing this (perhaps more for reasons of high voltage isolation), though it relies on there being a direct line of space between the front panel knob and the control in the back.
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Originally Posted by stratus46 View Post
I'm probably being a heretic here but I typically float the connectors from the chassis so have to connect both ends of the shield. Using the chassis as a conductor is a fine way to create ground loops.

G
Yes. Definitely have the input connector ground insulated from the chassis and have its own wire that goes directly to the ground of the circuit the signal goes to. If there's chassis or "ground loop" current (mains current capacitively coupled through power transformer windings) through the signal cable's ground, this should minimize its effect.
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Old 13th September 2011, 04:16 AM   #25
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Quote:
Originally Posted by stratus46 View Post
I'm probably being a heretic here but I typically float the connectors from the chassis so have to connect both ends of the shield. Using the chassis as a conductor is a fine way to create ground loops.

G
I isolate connectors from the chassis as well, but I don't understand how this forces the 'grounding' of the shield at both ends.
By using the signal ground conductor and the shield both as conductors, aren't we inviting a ground loop?

Just curious. Grounding gets complicated........
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Old 13th September 2011, 09:38 PM   #26
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Quote:
Originally Posted by benb View Post
It sounds like you've already got your mechanical layout done and are running the wires back and forth/front and back through the chassis, but there are ways to substantially shorten the signal path. Selector switches on the front could operate relays in the back instead of switching the signals directly. Volume control potentiometers can be in the back, operated by long shafts that come through the front panel (and of course rotary selector switches can be controlled this way too). I recall Heathkit ham radios (SB 300/400 series) doing this (perhaps more for reasons of high voltage isolation), though it relies on there being a direct line of space between the front panel knob and the control in the back.

Yes. Definitely have the input connector ground insulated from the chassis and have its own wire that goes directly to the ground of the circuit the signal goes to. If there's chassis or "ground loop" current (mains current capacitively coupled through power transformer windings) through the signal cable's ground, this should minimize its effect.
Yeah but I didn't think about that beforehand. Again, the runs aren't that long, but I do have some other boards that are far away and long runs cannot be avoided. Perhaps I could have done it another way but between the headphone amp and a sub equalizer board and the actual amp boards, the signal would be all over the place anyway.

My case is wooden so it's pretty hard to accidentally ground it to the case. =D Also means I have crappy EMI protection but oh well.

Good point though.

Last edited by FenderBender11; 13th September 2011 at 10:03 PM.
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Old 14th September 2011, 12:00 AM   #27
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I have some Belden #8450 and some #8451 on my bench.

I don't think that #8452 is the correct part number.
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Old 14th September 2011, 01:30 AM   #28
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Note sure where you saw #8452, but I recomended the #8451; stranded conductor. #8450 is solid wire version of same.
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Old 14th September 2011, 07:28 AM   #29
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Originally Posted by thaumaturge View Post
Note sure where you saw #8452, but I recomended the #8451; stranded conductor. #8450 is solid wire version of same.
Doc
We use 9451 at work. The only difference from 8451 is the foil is bonded to the jacket on 9451 so it's a little easier to strip the jacket.

G
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Old 15th September 2011, 11:46 AM   #30
marce is offline marce  United Kingdom
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Yet to shield for RF does not one have to connect the shield at both ends...
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