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Old 2nd July 2012, 04:41 PM   #1131
bcmbob is offline bcmbob  United States
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You are correct - and I was not recommending the use of coax for volume pot wires. I only used coax as a tool to visualize the shielding concept. Maybe a giant python just after it swallowed a water buffalo would have been a better example.
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Last edited by bcmbob; 2nd July 2012 at 04:51 PM.
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Old 2nd July 2012, 09:31 PM   #1132
KSTR is offline KSTR  Germany
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Originally Posted by bcmbob View Post
Another way to visualize the concept would be the signal - shield design of standard coax cable. The metal box that houses the pot simply acts like a balloning of the shield over a short distance.
Yes, that exactly is the point for efficient electrostatic shielding. Depending on the thickness of the aluminum housing and on how good the electrical contact is along the seamline(s) of the box and the lid(s) this will also afford good magnetic shielding at moderate and high frequencies.

At low frequencies twisting all of the (short) signal lines per channel with the corresponding return (GND) lines does the job (but magnetic coupling is only an issue when the magnetic fields are very strong indeed), but you must take care not to build literal ground loops inside the box (keep the loop area of the GND connection wiring in itself as small as possible, that is, avoid any loops).

For the same reason the GND shall only be connected at one single point -- solder the four lugs of the RCA's together, the RCA barrels will provide the contact to the box.

Click the image to open in full size.




For the outside world, twist all interconnects together, too, and at the point were you must split between input (source) and output (amps), keep the L and R lines together as much as you can.

Finally, route power cables also along that cable buss, again keeping all cables from/to a device together (interconnects with good shielding properties, and some experimentation is required.

It's all about keeping sending and receiving loop areas as small as possible.
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Last edited by KSTR; 2nd July 2012 at 09:35 PM.
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Old 2nd July 2012, 10:08 PM   #1133
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Klaus,

the My_Evo Rev A grounding scheme, which is the one I've intention to use, has a pseudo Class II approach:
  • Safety earth is not connected
  • PCB power ground is connected to chassis
  • RCA connectors are insulated from chassis
  • R11 is, obviously, in place.
What do you think about it?

A thing that I've yet to figure out is where to connect transformer's shield, chassis or safety earth.

Thanks in advance
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Old 2nd July 2012, 10:22 PM   #1134
bcmbob is offline bcmbob  United States
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Thanks Mr K. That is very clear. I'll be building one soon.
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Old 3rd July 2012, 12:37 PM   #1135
bcmbob is offline bcmbob  United States
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Hey Dario. I'm under the impression the info KSTR has posted is primarily for use with a separate self-contained pot that would be placed between a source and a power amp via interconnects. Something more useful in testing than in final application (though the shielding can be beneficial in all situations). Not the same as what you are describing in post #1133.

I'm also thinking "Safety earth not connected" has to do with hum as discussed earlier, but how does that effect the general safety/shock hazard present in any amp design? Does the PCB power ground to chassis address that?
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Old 3rd July 2012, 12:55 PM   #1136
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Hey Dario. I'm under the impression the info KSTR has posted is primarily for use with a separate self-contained
Sure, in fact I'm not asking Klaus about it but what he thinks of the Evo Rev A grounding.

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I'm also thinking "Safety earth not connected" has to do with hum as discussed earlier, but how does that effect the general safety/shock hazard present in any amp design?
It's not directly related with hum, Mauro on his Rev A paper talks about 'weak interactions' (I've no idea what he mean).

A disconnected safety earth implies Class II construction (double insulation) which basically should mean that all precautions must be taken so that in case of a fault no high voltage is present on the chassis.

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Does the PCB power ground to chassis address that?
No
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Old 3rd July 2012, 01:11 PM   #1137
bcmbob is offline bcmbob  United States
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O.K. Thanks.

Sorry to be so slow to understand, but what ground category/design is the Fremen Edition? Can you describe in a little more detail those "precautions" an FE builder should keep in mind.

Probably just basic stuff, but I fear I may have introduced a bit of confusion over my last few posts.
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Old 3rd July 2012, 01:49 PM   #1138
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Quote:
Originally Posted by bcmbob View Post
O.K. Thanks.
As always, you're welcome Bob

Quote:
Originally Posted by bcmbob View Post
Sorry to be so slow to understand, but what ground category/design is the Fremen Edition?
Class II is referred to chassis and the whole construction of the device.

Not directly related to the FEs.

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Can you describe in a little more detail those "precautions" an FE builder should keep in mind.
It's what I'm trying to figure out too...

I suppose, for instance, that all power wires should be fixed, all power connectors are insulated, that all wiring is done so that in case a connector disconnects it can't touch chassis and so on...

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Probably just basic stuff, but I fear I may have introduced a bit of confusion over my last few posts.
I don't think so.
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Old 3rd July 2012, 02:00 PM   #1139
billo44 is offline billo44  United Kingdom
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Quote:
Originally Posted by bcmbob View Post
O.K. Thanks.

Sorry to be so slow to understand, but what ground category/design is the Fremen Edition? Can you describe in a little more detail those "precautions" an FE builder should keep in mind.

Probably just basic stuff, but I fear I may have introduced a bit of confusion over my last few posts.
I know you are being overmodest Bob,... I will give my own 'parent of younger children' interpretation of grounding...

Any electrically conductive external part of a DIY audio project, which a person could conceivably touch, suck, bite, or lick, has to be connected to a robust safety ground by a physically secure crimped connection.

If you have noise as a result of following this grounding plan there must be ways of resolving it without potentially killing yourself or your loved ones.

I think they play a lot of New Age music in Hell so I don't want to get there any earlier than I have to .


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Old 3rd July 2012, 02:17 PM   #1140
bcmbob is offline bcmbob  United States
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Thanks Guys We will probably get deeper into the subject when the RC builds start taking shape.

Bill, You'r too funny !
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