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 Post subject: Grounding Techniques
PostPosted: 09 Aug 2009, 07:08 
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Joined: 13 Jul 2009, 20:01
Posts: 92
Location: Space Coast Florida
I am looking for some ideas and best practices for ground in a tube amp.

My construction is an aluminum chassis and I plan on point to point wiring.

I am considering taking a single sided PCB board (un-etched) and sandwiching that to the underside of the chassis by mounting it with the tube sockets. In other words, the machine screws that hold the sockets would also hold the PCB board against the underside of the chassis.

This un-etched PCB board would act as the signal ground plane and all grounding would be done directly to that plane. If I elevate the plane slightly above the aluminum chassis I could run the 6.3 VAC heater wires under the plane and keep their AC signal from injecting into the audio path.

The PCB would "grounded" to the chassis at a single point. To do this I would isolate the machine screws from the PCB ground plane by milling away the copper at the screw holes and use only one machine screw centrally located with star washers to electrically contact the PCB board to the aluminum chassis.

Components that require grounding could be directly soldered to the PCB and terminal strips could also be attached onto the PCB for interconnections that are not grounded.

My question is, is this a good technique for signal grounding?

Thanks in advance,

Loren


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 Post subject: Re: Grounding Techniques
PostPosted: 09 Aug 2009, 11:24 
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Joined: 04 Oct 2008, 11:29
Posts: 375
Location: Chillicothe, Ohio
I've seen articles from Mr. Pete Millett where he uses a method similar to what you describe. Seems like a great idea.

http://www.pmillett.com/829b_amplifier.htm

http://www.pmillett.com/elinear.htm


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 Post subject: Re: Grounding Techniques
PostPosted: 12 Aug 2009, 10:25 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I'm confident it will work, but it my be unnecessary. Careful wire and component placement can achieve wonders. As an alternative (one I use on occasion) is to isolate the power supply in its own sub enclosure and use DC on the heaters of tubes. With a metal chassis you are virtually assured of a very quiet project. One area that a number of builders seem to miss is that the B+ needs to be very clean. Any noise there will show up in the output.

Let us know how the project comes out.

Good listening
Bruce

UPDATE - Grounding and Shielding for your DIY Audio Projects by Bruce

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 Post subject: Re: Grounding Techniques
PostPosted: 21 Apr 2010, 14:39 
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Joined: 14 Oct 2008, 17:35
Posts: 901
Location: Dartmouth, Nova Scotia
will there be noise created by having all input/output RCA jacks mounted directly to the chassis without insulating washers?

It seems that this would introduce noise into the audio signal as the chassis houses all of the noisy parts, I really don't know but I think there is a ground loop potential. :confused:

I don't have any insulating washers for the RCA jacks (too cheap to include any) and carving a piece of wood to mount them did not work out too well.

What wiring suggestions are there, I am making a preamp with a phono stage and want the best wiring and lowest noise possible.

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 Post subject: Re: Grounding Techniques
PostPosted: 21 Apr 2010, 15:20 
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Location: Vänersborg, Sweden
I'd make a sub-chassis for the phono connectors, insulated from the rest of the chassis.

Here's an article about grounding, btw: Audio Component Grounding and Interconnection

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“If you don't know where you are going, any road will get you there.”
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 Post subject: Re: Grounding Techniques
PostPosted: 22 Apr 2010, 09:28 
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Location: Canada
Soundbrigade wrote:
the phono connectors, insulated from the rest of the chassis.

Hi.

Yes, I would make sure ground plates of all I/P & O/P jacks are insulated from each other & the metal chassis. [/b]
c-J

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 Post subject: Re: Grounding Techniques
PostPosted: 25 Oct 2016, 11:42 
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Joined: 29 Nov 2009, 13:17
Posts: 29
I just read the excellent article by Bruce which referred me to this thread (apologies in advance for resurrecting).

The thing that occurred to me in the article was that a ground scheme that seeks to isolate power ground from signal ground might utilize a single point (e.g., near the input jacks) to ground the signal as described in Bruce's article. Why, however, can you not (or can you) use the chassis isolated AC mains ground as a suitable ground for the power supply as well. It seems that this might absolutely keep any power and signal issues completely separate. But it doesn't seem like common practice and so there may be some reason that this is an untenable approach.


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 Post subject: Re: Grounding Techniques
PostPosted: 25 Oct 2016, 13:29 
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Joined: 07 Dec 2015, 14:21
Posts: 135
Take your schematic and draw all the current loops.

Now make these loops as short as possible.

It's as simple as that.


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 Post subject: Re: Grounding Techniques
PostPosted: 25 Oct 2016, 19:43 
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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

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 Post subject: Re: Grounding Techniques
PostPosted: 26 Oct 2016, 00:10 
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Joined: 07 Dec 2015, 14:21
Posts: 135
I am still in the camp of don't follow a "recipe". Follow the currents.

To be more specific and add to Bruce's comment about hum from mains via an earth safety loop.

Choose the proper power line polarity on each component. Noise from the power line in the form of AC leakage current will be transferred to the core and frame of the power transformer through the parasitic capacitance. Because of the way a power transformer is constructed, the parasitic capacitors are different values; and because the neutral power line is connected to the safety ground, the amount of noise on the two sides of the power line is different. These two factors work together to cause the amount of leakage current to be different depending on the polarity of the connection of the power to the transformer. The result is a voltage, with respect to earth, impressed on the chassis. It is most unlikely that this impressed voltage will be the same on two different chassis in the audio system and when those chassis are connected together, noise voltage will flow in the interconnection.


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