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 Post subject: Re: Grounding Techniques
PostPosted: 02 Dec 2016, 08:34 
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Forgive me for being a little bit snarky here - but your notes are for the ideal world. Which, as we have all learned often diverges from actuality.

Please note the interpolations:

atharva wrote:
Can I summarize this as....

1. Chassis directly connected to mains power ground (Earth/3rd leg of the IEC connector) - protects from shock

Only in the ideal world. If the mains power ground is compromised in any way, and/or a better ground is nearby, if the chassis is above ground for any reason, a shock potential remains. Here is only one scenario: Your mains ground is 30 developed meters (100') from the panel. Using 12-gauge wire, comes to about 0.16 ohms, all good. Now, compromise that ground due to a poor connection somewhere, or it is at the end of a daisy chain, or there is 30 feet of BX in the loop. Resistance may be as much as 10 ohms, or more. Which will give you a current potential of about 12 A @ 120V across the ground line. So, if there is a better ground somewhere else all that current may decide to go 'that way' instead. And as you (assuming you are a healthy adult) are, effectively, a 10,000 ohm, 1/4-watt resistor, that may be enough to cause damage.

2. Power ground - This is the -ve pin of the DC supply (possibly after transformer and rectifier). This is connected to #1 via the resistor and capacitor in parallel. It handles the leakage current in the circuit.

Yes.

3. Signal ground - (outer connector of the RCA jack) - This is connected directly to #1.

Yes.

Please confirm.


This is why I am a bit of a bug on grounding and do not rely on the mains ground alone - ever.


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 Post subject: Re: Grounding Techniques
PostPosted: 11 Dec 2016, 23:03 
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Many thanks to Bruce for writing up this excellent article on grounding for DIY projects.
For some reason however I'm left with even more questions than answers after reading the comments in this thread and the article a few times over :|
I'm building a D-class amp using 2 identical D-class amp modules, and although the setup is fairly simple, the grounding remains unclear.
Both of these D-class amp modules need to be powered and have their own mains AC terminals (L/N/PE).
So how I interpret the article for my build:

1. connect input ground from IEC C14 connector to chassis;
2. connect both modules' PE (ground) to that very same spot, using one parallel resistor and cap PER MODULE (?);
==> or alternatively to the above #2: use a single parallel R + C setup, and arrange for both PE ground wires from the modules to collide right before this parallel setup;
3. connect the pin1's of both XLR's straight to chassis;
==> or alternatively to the above #3: do I run the signal ground wire from the D-class module straight to XLR pin 1, without connecting the latter to chassis ground?

Any help would be appreciated :thumbsup:


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 Post subject: Re: Grounding Techniques
PostPosted: 29 Dec 2016, 13:45 
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Joined: 14 Nov 2016, 21:03
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Hi Guys!

I'm currently working on my 1st tube amp project. It's an adaptation of a PCB design where the PCB is no longer available. After reading multiple threads and articles I think I have a good plan figured out.

I'm using separate ground busses for the PS, heater "center tap", left preamp, right preamp, left power amp, right power amp. All the grounds are terminating to a small bus at the inputs. See the illustration below...

My question is using the X2 cap / resistor Bruce mentions in his article. Where in my circuit should this go? My guess is between the star buss and the chassis (chassis ground 2 in my diagram)?

Any direction on this would be great as I understand grounding can make or break a project.

THANKS!

Image


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 Post subject: Re: Grounding Techniques
PostPosted: 29 Dec 2016, 17:40 
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Location: Arizona, USA
Hi, I'm not sure what you are doing. It looks like lots of things are going to the chassis ground. The only things that should go there are the AC mains ground and the X2/Resistor combo from the main circuitry. Sometimes a chassis ground terminal is used to interconnect gear. I often do this between a preamp and phono turntable. Perhaps I am misinterpreting what you are doing but it looks wrong to me.

Good listening
Bruce

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 Post subject: Re: Grounding Techniques
PostPosted: 29 Dec 2016, 17:50 
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Hi SamX, Somehow I missed your question when it was posted. A simple drawing of how you want to hook things up would be helpful. Without it I'll take a guess....I would use separate X2/resistor combos on each amp and keep everything separate as much as possible. The ground in each balanced connection might go to the chassis, but I would personally run it to the circuitry ground and see if it works well there. I would use which ever way introduces the least noise. This assumes you have actual balanced circuitry in the amps. I believe I would keep the outputs separate as well unless you are forced to use a common ground.

Good listening,
Bruce

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 Post subject: Re: Grounding Techniques
PostPosted: 29 Dec 2016, 18:24 
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gofar99 wrote:
Hi, I'm glad to hear that someone reads the stuff (especially the stuff learned the hard way). The issue is ground loops. A frequently over looked one is through the AC mains. If the signal ground is connected directly to the chassis and it to the AC mains earth ground then anything else used with it may a similar path. This will become an alternate path and almost always cause a hum. One of the most frequent paths I find are as you might expect in Pro gear. The mix of various types of grounding is why you find "ground breakers" and "ground lifts" in many set ups.

Good listening
Bruce



Thanks Bruce! And thanks for the article you wrote.

You are correct in that as of now everything is connected to the chassis. In my diagram chassis ground 1 is for the AC module. Chassis ground 2 is where all my buses converge and then there is a single wire to the chassis. I guess I want confirmation that this is where my x2 / resistor should go? Between the converged grounds (star ground) and the chassis. Replacing the singe wire to the chassis of course.

Thanks again!

edit... here's what I'm thinking (see x2 cap and resistor at chassis ground 2)...

Image


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 Post subject: Re: Grounding Techniques
PostPosted: 29 Dec 2016, 20:21 
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Location: Arizona, USA
Hi, OK, then the white dots are not directly attached to the chassis and the X2/Resistor goes between then and the chassis at point 2 and the AC mains connect at point 1. It should work. My preference is that the two points be at the same location to prevent any current (however small) from traveling through the chassis from one to the other. If the power filter is not in metalic contact with the chassis at the entry point (looks like a wood case) I believe I would route the ground wire from it to the place marked point 2. If it is in contact it will still probably be OK, just not what I would call ideal.

Good listening
Bruce

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 Post subject: Re: Grounding Techniques
PostPosted: 30 Dec 2016, 11:40 
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gofar99 wrote:
Hi, OK, then the white dots are not directly attached to the chassis and the X2/Resistor goes between then and the chassis at point 2 and the AC mains connect at point 1. It should work. My preference is that the two points be at the same location to prevent any current (however small) from traveling through the chassis from one to the other. If the power filter is not in metalic contact with the chassis at the entry point (looks like a wood case) I believe I would route the ground wire from it to the place marked point 2. If it is in contact it will still probably be OK, just not what I would call ideal.

Good listening
Bruce


You are correct Bruce. The white dots are isolated terminal posts, so they are not electrically connected to the metal top. And yes the sides are made of wood. I'll plan to run a wire from the ground of the AC input module to the same spot that the X2/Resistor connects to the chassis.

That leaves two more grounds in question. The ground from the secondaries on the Output Transformers and the internal shield between primary and secondary of my torrid power transformer. Could these 2 connections be made right at the AC Module since they should not be carrying current under normal situations?

Thanks again for all your help on this!


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 Post subject: Re: Grounding Techniques
PostPosted: 30 Dec 2016, 12:11 
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Just a note unrelated to grounding: Shouldn't R13 be tied to the junction between C1 and R1? The wire appears to have disappeared between the first diagram and the second.

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 Post subject: Re: Grounding Techniques
PostPosted: 30 Dec 2016, 13:11 
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Joined: 14 Nov 2016, 21:03
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Suncalc wrote:
Just a note unrelated to grounding: Shouldn't R13 be tied to the junction between C1 and R1? The wire appears to have disappeared between the first diagram and the second.


Good eye! Somehow that wire got deleted. I'll add it back in :up:


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