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Old 9th January 2002, 10:34 PM   #1
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Default grounding schemes

hey out there, (or is that in here)
can anyone direct me to a resource that describes the best grounding schemes for aleph, or any other amplifiers, ie. where to ground different parts, ps, channels, outputs, etc.? also, what gets connected to the earth ground, all, some yadda, yadda.

thanks,
scott
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Old 9th January 2002, 11:34 PM   #2
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Default Great question

What is ground anyway?

Grounding of equipment wrt outlet power is relatively well understood. Some equipment is grounded, other types don't even have a ground connection to the wallm, some outlets don't have ground, and the X power amps are not grounded to signal. Method og grounding here is also a function of how your power grid is set up and feeds your home.

In your power supply, if your transformer has distinct windings for +/- rails rather than just a center tap (4 wires instead of 3), you should make sure that you use two bridges instead of just 1. This will reduce currents in ground to a minimum and likely lower your base noise on the ground itself.

Signal ground is a much misunderstood subject even for professional designers. As a DIY'er you have full control of this important parameter. I cannot profess to be an expert on the issue, but I recommend that people who are interested do a search on the Internet as there is a lot of information out there. There is not one single answer -- it will vary with application (NP said for example that the Pearl should be "grounded" near output). For low level signals it may also be of interest to use ground planes to create low impedance paths that also offer some "shielding". For higher current applications one is probably better off using wires so one can control where the magnetic fields due to current are created in the hope that they don't interfer with sensitive lower level signal paths.

The most basic DIY principle though is that there should only be one connection between "The ground" (whatever that is) and the chassis. This is termed "star grounding scheme". This means that no ground current can flow in chassis as there is no connection to anything else. I kind of like my signal more or less floating, perhaps referenced to chassis ground by a resistor, perhaps 1k would be a good starting point. If you use power line filtering, yo might already be in trouble since many power line filters make a virtual ground to the metal which you might not even have considered. Now that is your star-point, make sure you have only one!

Another golden principle is to separate digital ground from analog ground whenever possible, and only connect together in one place if necessary, perhaps with a passive component such as a small inductor or a resistor.

The X-series is fundamentally balanced. That means that the output has two live wires rather than a live + "ground". I like that. For me it means that the high power output is not messing with signal ground at all (not directly at least).

As equipment purchased is invariably wired differently, you might be in a spot of trouble even though the individual pieces are OK on their own.

I am sorry that I cannot give an simple and all encompassing answer, perhaps greater designers can. In this forum, we can only hope that Nelson will provide a "Grounding scheme commentary for DIY'ers".

Petter
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Old 10th January 2002, 12:09 AM   #3
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petter,
WOW! thanks. i read your post a couple of times and i have a couple of questions. i have two xformers,center-tapped, for my power supply with two bridge rectifiers. now, should use a separate star ground (chassis) for each channel, or just one? the reason i ask is that i recently built a pre-amp and there were two separate grounding points for each channel.

secondly, is the ground loop( the common ground for the actual channel amp) just a common point that is then routed to the grounding point on the chassis?

i'm trying to understand this as much as possible for safety and for theory as well. i guess that's one of the pitfalls of these open forums is that you can get someone that knows very little about a subject right along with you guys that have a good handle on the subject. I really appreciate your time on this,
thanks,
cheers,
Scott
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Old 10th January 2002, 12:39 AM   #4
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1. I am assuming that you have a stereo power amp with 1 transformer for output stage, 1 for input stage. If center tapped, you are screwed. You cannot get mileage out of the dual bridge (for input and separately for output, total of 4 bridges) trick unless your transformer exposes both windings as separate entities. The clue here is that you hook up the diodes, and then after that you hook the 0V lines together and move on with 1 wire.

Now, if you had 2 center tapped transformers, one for each +Vcc and -Vcc, you do have two completely exposed windings except they are not magnetically connected. Don't worry about that -- and ignore the Center tap. If not connected, there is no current there.

2. Not quite with you -- if you mean the theory of a ground loop where the loop is essentially a single point, yes. However, since we are talking about many "grounds, whatever that is anyway", it can be tough. If you have a CT situation with quite a lot of noise on the ground, hooking up signal ground can cause som problems. If you hook up the signal ground in one corner of the device and the PSU ground in another corner, you have a bad situation as you likely pass signal through chassis!

Single ended connections (standard RCA) usually pass gound and live.

Balanced pass Live, -Live, Ground (which is not neede as it can be derived by taking mid point of Live and -Live) and Shield. Some of these are not connected all the way through! Pretty cool eh?

Now for some theory of balanced signal.

Take two wires:

------------ Live signal + noise picked up along the way

------------ -Live signal + same noise


Subtract at input

Live + noise - (-Live + noise) = 2 Live + no noise
(provided noise is identical which it is not, but it should be close if wires are in close proximity etc.) It is so simple and quite beatiful.


Some more on ground loops (Do not considre this as the all-true reference!):

With RCA connectors and single ended signals, you are passing a signal ground between components where you really don't know what the guy before you did to you (groundingwise). Your mother should have tought you better. Bad DIY person. BAD BAD BAD! Open that SOB source component up right now (make sure you void the warranty as well and add a line filter and a detachable cord for convenience, especially if it is a digital component) and figure out why you have that ground loop problem which is causing you so much grief.

If you are unlucky, you get a ground loop running through the signal RCA cable an back though mains ground to where you started counting. That my friend is very poor star grounding if you see the big picture. You could solve it with a cheater plug which is effectively what I do by design of what my electrician gave me at home build time -- it does not have ground as it is not required by law for that zone (whereas it is required in my bathroom and kitchen).

Petter
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Old 10th January 2002, 07:57 AM   #5
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http://members.tripod.de/Promitheus/ground_amp.htm
take a look here. this is a schematic from a book I have.
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Old 10th January 2002, 09:39 AM   #6
AuroraB is offline AuroraB  Norway
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Grounding and shielding techniques are probably one of the most confusing topics in the electrical trade. At work, about a foots length of shelf space is filled with litterature on this strange topic alone.

The most important and basic theme is to understand the difference between safety ground and signal ground.
Most countries' electrical regulations would require that your equipment is connected to a power ground grid for safety reasons. Signal ground may not necessearly be the same point, and here the confusion starts....

In RF , the common practice is to connect to signal ground as many places as possible , in order to creat a low impedance ground connection, to enhance the shielding effect. It is fairly common knowledge that this will/can cause circulating currents in the grounding network, most often AC with the powerline freq. , or doubled if bridge rectifiers are used. This is audible, as every audio enthusiast most painstakingly knows !

Therefore, in audio, the most common practice has been to adopt the "single point" grounding scheme, where all subcomponents share a common internal grounding point , e.g inside an amplifier.

If your pre and power amp are both connected to safety ground via the power connector, the ground loop is closed around the signal cable, and --there the old humming brigade is loose again.....

One tip for DIYers, also often seen in professional equipment, is to use the signal ground as the reference point, and then, if required or wanted, connect the safety or power ground, to this ref.point by a 1-10ohm safety resistor. This helps to swamp any ground loops.
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Old 10th January 2002, 02:41 PM   #7
tiroth is offline tiroth  United States
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Rod Elliot has some discussion on proper grounding on his site and at least two different "ground loop breaker" circuits that do not compromise the safety ground.
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Old 11th January 2002, 07:38 PM   #8
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I have two favorite "ground loop breakers", a power
Thermistor and a rectifier bridge.

The Thermistor works by being an ordinary 10 ohms
or so, but in the event that a lot of current goes through
the ground circuit, it reduces to a much smaller value. A
tip of the hat to Frank De Luca for that invention.

The rectifier bridge will conduct a lot of current when you
go over .7 volts, enough of a barrier for noise, but a good
conductor in event of failure. One advantage to the
rectifier bridge approach is that it can isolate to channels
of ground both from each other and earth at once.

You will see the use of the Thermistor in most of my
DIY amp articles, and the rectifier bridge on the
Zen lite article.
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Old 11th January 2002, 09:44 PM   #9
hifi is offline hifi  Sweden
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if one have a power transormer with dual outputs if each is given a rectyfier bridge and a cap to form a +/- supply where should the ground connection between them be?

1 directly between the rectyfierbridges

2 after the caps (individualy wired to each bridge)

3 dosnt matter ?

/micke
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Old 12th January 2002, 02:15 AM   #10
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@ the ground of the caps.
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