Wire runs within the chassis. Shielding properly. - Page 2 - diyAudio
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Old 5th February 2013, 04:39 PM   #11
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Quote:
Originally Posted by gootee View Post
The main thing is that the signal and signal ground should never get separated. The signal ground needs to stay ONLY right next to the signal, all the way from the source output to the input shunt resistor at the first active device in whatever amplifier it goes to.

If the ground connects to anything else along the way, and can also take a different path, that doesn't stay right next to the signal, then the enclosed loop area between the signal and ground will be a big antenna. (Similarly, two untwisted wires, with any gap or space between them, would not be good.)

So your switch should be switching both the signal and the ground, and should connect both to only one source and only one destination at a time.

If the switch connects one or more of the grounds from different amps together, that would not be good.

I would much prefer to use shielded twisted pair. Then the shield is just a shield and should NOT be connected to the signal ground. Then you would connect the shield to chassis ground at one end only, always.

With a shielded cable that has only one single inner conductor and an outer "shield" that is also the signal ground, you should always need to connect the shield at both ends, if everything else is set up correctly. Otherwise you would force the signal ground to find some other route, which would make a large enclosed loop area between signal and ground, which makes a much better hum (and RF) antenna.
Alright. So from the switch, I should be making multiple runs? Right now, if you understood my correctly, I make one run to this sub preamp/filter board, and then I just use the input terminal blocks there to go to the left and right channel because it saved wire and the amp isn't that spacious.

But you are proposing that from the switch, I should "branch" out directly from the switch contacts?

Also, I do not have a metal chassis, so I guess I'll just connect signal shield to the third prong on the IEC inlet? I can do that pretty easily. However, this shield should not be attached to signal ground...at all?

---

I also have two potentiometers that I want to hook up using twisted-quad (that has a shield). This should should also get connected to "chassis" ground?
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Old 5th February 2013, 10:11 PM   #12
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One simple rule is this:

Always connect the shielding at the end wich have the highest impoedance. (At the input of every board)

This ends up in to solder the shielding near the input of the amp-board.
If there is separated signal and power earth on the board, it will need one lead from the earth at the signal input down to the powersupply ground. And another lead from the power-ground on the board down to the same point on the powersupply.
Additional lead fron the ground of the input connectors, and from speaker ground bindingpost. All in a "star" to the point at the powersupply.
Any signal (line-level) wich arte to go out of an amp, should have the shielding solderet at the output connector with a groundlead down to the power supply. This signal cable should NOT have its shielding soldered to the board, but left insulated.

This way I have buildt hiss and humfree amplifiers for quite an amount of years now. Oh yeah, even in unshielded cases.

I ALWAYS keeps PE (The power inlet ground) separated from signal ground.
If this has to be connected anywhere, I would recommend to connect that to the chassis, and then have a 10M resistor in paralell with a 1uF 630V capacitor to the signal ground (Internal power supply ground. Then I would have a switch between the CAP and PE to separate chassisground from signal ground just for the giggles. In some areas it seems as a good idea to have AC coupling between PE and signal ground.
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Last edited by TANDBERGEREN; 5th February 2013 at 10:16 PM.
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Old 5th February 2013, 10:30 PM   #13
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Originally Posted by TANDBERGEREN View Post
One simple rule is this:

Always connect the shielding at the end wich have the highest impoedance. (At the input of every board)

This ends up in to solder the shielding near the input of the amp-board.
If there is separated signal and power earth on the board, it will need one lead from the earth at the signal input down to the powersupply ground. And another lead from the power-ground on the board down to the same point on the powersupply.
Additional lead fron the ground of the input connectors, and from speaker ground bindingpost. All in a "star" to the point at the powersupply.
Any signal (line-level) wich arte to go out of an amp, should have the shielding solderet at the output connector with a groundlead down to the power supply. This signal cable should NOT have its shielding soldered to the board, but left insulated.

This way I have buildt hiss and humfree amplifiers for quite an amount of years now. Oh yeah, even in unshielded cases.

I ALWAYS keeps PE (The power inlet ground) separated from signal ground.
If this has to be connected anywhere, I would recommend to connect that to the chassis, and then have a 10M resistor in paralell with a 1uF 630V capacitor to the signal ground (Internal power supply ground. Then I would have a switch between the CAP and PE to separate chassisground from signal ground just for the giggles. In some areas it seems as a good idea to have AC coupling between PE and signal ground.
Thanks. I'm having a hard time understanding some parts of your post.

Just still confused where and to what the shielding should be connected.

Here are some notes about my amp:

-Signal and power ground are shared

-Wooden chassis. I do have PE connected to the amp ground (isolated by a CL-60 inrush current limiter). This was a suggestion by another diyaudio member a while back.

- Signal comes from RCA jacks, goes through a switch (which can switch between headphone out or power amp out). If power amp out is chosen, three things need signal. Left channel, right channel, and subwoofer.


I have twisted pair shielded cable. Mogami is the brand. Where should the shield be connected and to what? To the protective earth? To signal ground?

I also have two potentiometers that are connected with long cable runs. I was kind of forced to do it this way because I made some other silly design decisions. I also have quad (four wire) shielded Mogami wire. I was planning on using 3 conductors for each potentiometer. However, I wouldn't be sure where to attach that shield either?



Thank you. I really appreciate the help.

Last edited by FenderBender11; 5th February 2013 at 10:34 PM.
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Old 6th February 2013, 03:55 AM   #14
gootee is offline gootee  United States
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Well your drawing did not show shielded twisted pair! It shows coax, like RCA cable! And it shows the shield as connected to audio signal ground!

Quote:
Also, I do not have a metal chassis, so I guess I'll just connect signal shield to the third prong on the IEC inlet?
If the shield is NOT CONNECTED, ANYWHERE, TO SIGNAL GROUND, then yes, you can connect it to whatever other ground point you want, I suppose. But only the connect the shield at one end of each cable, to ground (BUT NEVER to "signal ground"). And make sure that the shield on the other end is connected to NOTHING.

What kind of connectors are on the ends of your audio cables (the ones you say are shielded twisted pair)?

Quote:
-Signal and power ground are shared
Quote:
- Signal comes from RCA jacks, goes through a switch (which can switch between headphone out or power amp out). If power amp out is chosen, three things need signal. Left channel, right channel, and subwoofer.

I have twisted pair shielded cable.
Just kill me now...
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Old 6th February 2013, 11:59 AM   #15
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Quote:
Originally Posted by gootee View Post
Well your drawing did not show shielded twisted pair! It shows coax, like RCA cable! And it shows the shield as connected to audio signal ground!



If the shield is NOT CONNECTED, ANYWHERE, TO SIGNAL GROUND, then yes, you can connect it to whatever other ground point you want, I suppose. But only the connect the shield at one end of each cable, to ground (BUT NEVER to "signal ground"). And make sure that the shield on the other end is connected to NOTHING.

What kind of connectors are on the ends of your audio cables (the ones you say are shielded twisted pair)?





Just kill me now...
I take that back. Signal and power are not shared. The amp sounded very good. So please don't say that.

Connectors? What do you mean? RCA?

They are soldered.
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Old 6th February 2013, 12:37 PM   #16
marce is offline marce  United Kingdom
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For proper shielding the shield should be connected at both ends., connected at one end it is an antenna, and provides no RF shielding. A better method is to either use an isolation transformer, or at least connect the shield through a ring of capacitors at one end instead of leaving it floating.

http://www.hottconsultants.com/pdf_f...onnections.pdf
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Old 6th February 2013, 02:52 PM   #17
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Originally Posted by marce View Post
For proper shielding the shield should be connected at both ends., connected at one end it is an antenna, and provides no RF shielding. A better method is to either use an isolation transformer, or at least connect the shield through a ring of capacitors at one end instead of leaving it floating.

http://www.hottconsultants.com/pdf_f...onnections.pdf
Ugh so many differences in opinions...
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Old 6th February 2013, 06:30 PM   #18
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here's another

i used no shielding on internal cables, just very thick hook-up wire

single star grounding (no sub stars at input resistor etc)

earthed aluminium case, directly connected to star

utter silence of course, you don't know it's on

Last edited by Robert Kesh; 6th February 2013 at 06:32 PM.
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Old 6th February 2013, 08:23 PM   #19
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Yikes. I guess I have some reading to do.
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Old 7th February 2013, 07:14 AM   #20
marce is offline marce  United Kingdom
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Start with Henry Ott, I have his book, which provides an excellent reference for all these sort of things. He is probably the number one authority on all this sort of stuff, shelding grounding schemes etc:
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