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Author Topic: Grounding techniques  (Read 42442 times)

teemuk

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Grounding techniques
« on: August 21, 2006, 05:28:13 AM »
This thread was started so that people struggling with humming amps could have an information resource that helps them to understand what’s going on. The internet is full of information but it is quite scattered and I hope this thread will develop to collect this information together. There are few resources I can recommend such as…

Epanorama: Tomi Engdahl, Ground loop problems and how to get rid of them (http://www.epanorama.net/documents/groundloop/) and Ground loops and equipment design (http://www.epanorama.net/documents/groundloop/in_circuit.html)

Randall Aiken, Star Grounding (http://www.aikenamps.com/StarGround.html)

R.G. Keen, Star Grounding in Tube Amplifiers (http://www.geofex.com/Article_Folders/stargnd/stargnd.htm)

I’m sure a more thorough search would reveal even more. From top of my head I have summed up few rules that I regard as most important. Feel free to participate to this thread by comments or presentation of methods that you have found important.


Update 30.01.2007
Some corrections to the terminology. Corrected some spelling issues and added a small description of "loop breaker" circuits.


1) The essential part is to start treating the grounding as a part of the circuit itself: Each time a part of your circuit makes a connection to common it will not have a reference of ideal zero volts. Instead, this connection is just the other end of conductor connected to the only real common point that can exist in the system - a conductor with resistance. Since the circuit stage’s current goes through this resistor, then according to U=IR the "common reference" point of the stage must have a voltage potential. It would be better to refer to these points as “common returns” not as commons.


2)  Different common spots and safety ground
Even a typical amplifier circuit can have at least three "grounds": Mains "ground", safety ground and secondary circuit ground, which really is not a ground at all. The first two should be ignored: Mains "ground" or neutral is NOT a ground either and should never be mistaken as one. It has zero volt potential but one should treat it as a conductor carrying mains return currents. Safety ground (of a device) is just an alternative for neutral in the case of faults. Safety ground has a sole purpose of saving you and from the viewpoint of removing hum and noise that should not make any difference whatsoever.

In practically all circuits, the reference used is not ground, it's common. A term common is better also because it indicates that the point might be "floating" and does not necessarily have a zero potential in reference to earth. Any voltage chosen from the secondary side can be used as the common reference: This is also the reason why you can get positive, positive and negative and negative voltage potentials from center-tapped transformers.

In some point of the house/mains wiring, the safety ground is connected to neutral. Usual location to do this is either inside the breaker box (right way) or inside the mains receptacle (works but is a bit unsafe). Having a permanent connection somewhere in housewiring is a safer than trying to make the connection by yourself inside the device since you have 50/50 change of succeeding if you can plug the power cord into the wall outlet in any direction. Since the chassis (safety ground return) and the common are usually tied together they will appear in nearly same potential. If the chassis is insulated from the common the common will float in whatever potential it sees best.


3) Choosing the right common spot
Only one true common point where the returns connect can exist in the circuit and therefore it should be selected with great care. Also, remember that current flows in loops. Consider these points:

a) Diode rectifiers make switching noise that appears as transients. These transients have the worst effect in close proximity to the diodes. You do not want switching noises to affect any other common returns. Ever wondered why commercial devices have those capacitors in parallel with diodes? Well, now you know.
b) Filter capacitors draw current as pulses. A filter capacitor charged by rectified signal never becomes “full” and never stops being charged, this is especially notable when the circuit’s current draw is high. Currents created by these charge pulses are high and form a loopfrom the rectifier to the filters. The loop - as always - includes common wiring as well. You want to keep these charge pulses away from any other common returns.
c) Using the center tap as common point and connecting it to chassis most likely prevents you from making any other high current common connections to chassis (ie. speaker jacks).

I would not recommend using either one of the first two as the common point. So far I have found the following arrangements ok:
a) Single supply: Transformer connects the rectifier, rectifier connects the main filter capacitors and capacitors connect the common point. All other common returns connect only the common point. Safety ground may, or may not connect this point directly.
b) Dual-supply: Center tap connects the main filter capacitors and capacitors connect the common point. All other common returns connect only the common point. Safety ground may, or may not connect this point directly.


4) Correct ways to route the common returns
A ground loop is formed if the return currents of one stage inflict the return currents of another stage. Most severe situation is when high current stage (ie. speaker load) return currents share the same route with the return currents of the input stage. Most common example is when a ripple containing supply return shares the return of the input. Since nearly all gain stages use only a common return as a reference, any voltage appearing at this point will be heard in the output. Differential input amplifiers (opamps etc.) are a little more tolerant against this than class-A discrete stages.

The common returns should be separated by their type: audio (signal) / power (supply) and high current / low current returns should never mix up, neither should analog/digital returns. All these will eventually connect each other in the best and correct place, which usually is the common point. If nothing else, you want to at least separate high current and low current returns as well as signal returns from other "dirty" returns. Make it a principle for yourself that connecting these returns together anywhere else than in common point is always a conscious risk of adding a source of hum or noise to the circuit.

a) Star grounding
Ideally, all common returns should be routed separately and connected to common point in a form of “star” in order to prevent the returns from capacitively coupling each other. This method is ultimately effective but very hard to construct in real circuits. Very often the result is just a massive amount of long wires that may catch interference. Many people question the effectiveness of star ground but the reason for this is that they have most likely done something wrong: Either they have very long wires that are highly inductive or run near hum sources, they have bundled a few returns or made a chassis connection. (A true star ground can have only one chassis connection. This connection is made from the common point itself). In latter two arrangements one no longer even has a star ground. I see no reason why a correctly made star ground should hum – ever.

b) Various bundled common returns
Bundling up common returns can make the "grounding" scheme more compact. This is advisable, and properly done will not increase the hum or noise substantially. Usual procedure is to bundle the returns of each stage together. However, this is a pitfall: Many people bundle the supply to the signal return and wonder why their “bundled star ground” hums. The reason is the topology is no longer a star ground and the supply returns are infested by – sometimes – high current ripple or other noise that comes from switching devices etc. Also, bundling up the input stage and chassis (where several other common return connections will be made) together is asking for trouble. A better way is presented next….

c) Ground bus
The signal common returns should be bundled together this way:

Lowest current stage -> higher current stage -> etc -> highest current stage -> common.

The benefit of this arrangement is that the common return currents of the higher current stages will not return to the common point through the lower current stages. Then, the supply wiring returns should be bundled together in the same manner. If, besides these, the returns of power devices and speaker load are routed separately there is a fair chance that one can bundle all preamp/low current stages of power amp returns together with no hum whatsoever. In the end you have only few return wires running to the common point. Even better chance to success is to use bundled returns from multiple stages. Most likely the "grounding" scheme still stays fairly compact. Also, all passive stages returns can be fairly safely bundled to the return of the preceding active stage.

d) Large ground plane
This was a very often used technique in older amplifiers and usually involves connecting a vast amount of common returns to chassis thus forming a large and low resistance path for all return currents. Sometimes this works, sometimes it doesn’t and I would not recommend this technique for anyone building their own amplifier unless you are willing to experiment with several prototype boards and layouts. The problem in ground planes is that the return currents choose the least resistive path - not the path we wish - and thus may interfere with each other. The use of either bundled ground or ground bus topologies is far more effective, less confusing and logical. At least with it one can control what way the currents return. For people fixing or tweaking amps ground planes, however, are a necessary evil.

A more common approach nowadays is to use the technique in PCBs, where – sometimes even a complete layer is dedicated to "grounding" purposes only. Properly done this is even more effective than using ground buses. But then again, the whole topology can be ruined by a simple mistake that happens to form a ground loop. (One can, for example, originate from connecting inputs to both PCB and chassis and connecting chassis to common). I have also seen circuits utilizing massive ground planes connected together by a single wire - thus the whole idea of the topology is ruined. In my opinion, a careful following of ground bus topology leaves less room for mistakes than reliying on massive ground planes.


A little more about safety ground...
As said, this is tied into the Neutral wire - usually in the breaker box of the house wiring. The safety ground connection should tie together all conductive parts that the user can touch. Make the connection near the place where the mains wiring connects the chassis and leave the safety ground wire longer than any other mains wiring so that it will be the last one to break loose if tension is applied to the mains cord. Be sure the chassis (or any part of it) will not corrode and break this connection by making it highly resistive. A use of teeth lock washers and lock nuts is advisable. If you ground heat sinks make sure a proper connection is made regardless of the non-conductive anodisized layer they might have. Bear in mind that the safety ground is effective only when it is connected in house wiring as well. All attempts to locate a hum problem should be started by checking the continuity of the safety ground.

Common potential does not neccessarily need a connection to safety ground. However, in guitar amplifiers, where the user can access common potential via the strings of the guitar, this is highly recommended since reference to earth prevents the common point from floating up to high potential. The connection may either be direct or indirect. Since a direct connection to safety ground may introduce ground loops when two devices are connected together the connection is sometimes made through a "loop breaker" circuit: This is usually a 10 ohm resistor in parallel with a 100 nF capacitor. The resistor introduces enough resistance to limit ground loop currents and the capacitor bypasses radio frequencies. Since in fault conditions the circuit can burn "open" it should have parallel high power diodes that pass fault currents through. Diodes usually burn "short" so the protection would remain. Note that the loop breaker circuits are illegal in some countries.
« Last Edit: February 02, 2008, 04:23:57 AM by teemuk »

idle_chatterbox

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Re: Grounding techniques
« Reply #1 on: August 30, 2006, 11:19:50 AM »
nice tutorial  8)

willy1usa

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Re: Grounding techniques
« Reply #2 on: September 28, 2006, 09:01:06 AM »
Also in the grounding / hum department is the word interference. I lived with various interference hums until I discovered shielded wire. I now use shielded wire for my inputs/outputs. Clip one end of the shield off, and run the other end to the star ground. This has really cleaned up a lot of my work. Also, on a budget, I keep an eye out at the flea mkts. for old computer speakers, usually for a couple bucks. Most of these have shielded wire. Some of the wire is too small for larger amps, but work very well for opamp/preamp circuits.

idle_chatterbox

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Re: Grounding techniques
« Reply #3 on: September 28, 2006, 07:34:16 PM »
agreed.

Old RCA cables that came with VCRs can be used as shielded wire too.

I haven't tried shielding the output wires, like you say. Big difference? I assume you mean wires that terminate at the speakers?

willy1usa

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Re: Grounding techniques
« Reply #4 on: September 28, 2006, 09:16:50 PM »
Yes, tight budget encourages inginuity. Some of these old computer speaker cables have 2 wires + a shield. Especially in opamp circuits, I'll use the 2 wires for +/-, then ground one end of the shield. Some cables have foil for shielding, and some stranded wire. I've cleared up quite a few hums with this method.

Great article on grounding. Everyone, at some time, have had grounding problems.

elwood

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Re: Grounding techniques
« Reply #5 on: February 29, 2008, 08:01:25 PM »
That's a great tutorial... thanks for posting it.

A note about PCBs and ground layout. I've done some high frequency video PCBs (>100MHz) where grounding, inductance, power supply bypassing is a real challenge. This, and designing for EMC compliance (which doesn't apply to analog audio designs.. at least in North America) has found me in the library and reading a lot of app notes about layout. What I've realized is that there is a lot of misunderstanding, but if you are more careful than you think you need to be, the results will work.

Bypass capacitors do a lot to stabilize power supplies near both digital and analog ICs. This can help a lot of misbehaving circuits. It's not a replacement for good grounding, but while we're on the subject I think that good power supply wiring and good grounding go hand in hand. Keep in mind that filter and bypass capacitors don't work at all frequencies which is why you often see several types and values side by side. Also remember that just like grounding, power supply sags in your circuit can cause unwanted oscillations in analog circuits and troubles in digital circuits too.

I personally like ground planes very much. With even just a 2 layer PCB dedicating most of the bottom layer to grounding can improve the success of layout because you're always just a via away from getting at ground. A common method of layout for boards with high and low power sections, or digital and analog sections is to partition the ground planes and connect them together at a single point. You need to be careful when running traces across the gap, but this lets you have the advantages of a ground plane for each section, and the advantages of the star or bus grounding scheme for the entire circuit.

Anyway, there are no golden rules in this game, but I'm just sharing with you my experiences. I suggest that everyone take apart stuff that works and have a look at how the designers did things. You might not like everything you see, but you'll learn a LOT about how much care in grounding and signal routing is enough for a specific type of circuit. You might be surprised what some designers get away with. There's nothing wrong with over engineering something as long as it doesn't significantly impact the overall cost. But there certainly is something wrong with a circuit that doesn't behave itself!

I know it's pricey, but I highly recommend the book "Noise Reduction Techniques in Electronic Systems":

http://www.amazon.com/gp/product/0471850683

It's old and not a very big book, but don't be fooled! There's a ton of great information in it. I found it quite an eye opener! There was a lot of stuff in there that I've never come across on the web.

R.G.

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Re: Grounding techniques
« Reply #6 on: February 29, 2008, 09:15:45 PM »
There is a progression from the premium approach to grounding being planar at far ultrasonic and RF toward send/receive pairs at low audio and DC. A ground plane approach is flatly wrong for high power at low frequencies. Matching send/receive planes is nice at low frequencies because of the low inductance and inherent capacitances to paired planes.

The problem with just a ground plane at audio is that you get returning signals and power (what I call "sewer ground") mixed locally with reference ground for amplifier circuits. One good example of how this is bad is using a chassis for a "ground plane" in some guitar amps. Another place you really, really need an isolated "ground" return wire is the power return from a speaker.

Yes, for high speed logic, RF and video, planar approaches are the place to start. It helps that the frequencies are so high that local decoupling can supply enough pulse energy to smooth things on the plane out. Leave out the local decoupling and the planes can't do it all.

One prototyping system I like a lot is called "dots". You use a punch and punch out 1x10E6 1/8" diameter "dots" from PCB stock. Then you use an un-etched PCB sheet with dots epoxied to it wherever you want a connection. Part leads go from dot to dot, or dip to the ground plane where you want ground. It's artistic, flexible, and fun.

numpsha

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Re: Grounding techniques
« Reply #7 on: March 04, 2008, 04:47:35 PM »
This a good "sticky".

I've referenced those linked articles for quite a while and appreciate the additional comments here, particularly those regarding mains wiring. It's been a while since I've wired "safety updates" on old 5-tube radios and guitar amps.

I think some of the pcb layout techniques used in RF/HF could prove useful in audio. F'rinstance, I recall some method of isolating an input by utilizing circuit traces around it; forget details or what it's called but should look into this stuff again.

Although it won't correct faulty design or faulty mains wiring, I use a surge and noise suppression unit to plug my gear into. It really works great to suppress EMI/RFI line noise plus it warns you of line faults. Comes in handy when playing in seedy bars with an ancient freezer out in the kitchen. Talk about serious power conditioning -- you should see the filter banks in this thing! Mine was a gift from brother-in-law but looks like $50 on the net. If interested, here's spec's:

http://www.tripplite.com/products/product.cfm?productID=99#applications

Obviously, don't use one with a two-prong adapter. :duh


Rob



teemuk

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Re: Grounding techniques
« Reply #8 on: March 04, 2008, 05:25:45 PM »
I think some of the pcb layout techniques used in RF/HF could prove useful in audio. F'rinstance, I recall some method of isolating an input by utilizing circuit traces around it; forget details or what it's called but should look into this stuff again.

I call those “guard tracks” or “guard rings”: A track fed with voltage from a low impedance source (i.e. buffer) is wrapped around the high-impedance input circuit. This prevents capacitive coupling from taking place (high impedance circuits are naturally more prone to it) and reduces leak currents. However, there is one rule: The voltage potential of input and guard track must be the same. Thus guard tracks basically only work with unity gain buffered applications.

casiomax

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Re: Grounding techniques
« Reply #9 on: May 01, 2008, 09:59:54 PM »
I have use a single side pcb and solder everything i need to ground over that one piece of pcb, this type of technique i also use to build RF circuits, sometimes its called dead-bug style. there is a similar technique called manhattan technique, which use several small cutted pcb to make island as a soldering pad.

JonnyBlade

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Re: Grounding techniques
« Reply #10 on: April 18, 2010, 07:48:04 PM »
I think you'll find the manufacturer's take great care in grounding their amps properly. Nobody invests years and even decades of advances on the core design they built their company into a new, advanced model line every other year yet does a piss job of grounding the circuits properly.

99% of the time, it's simply that the ground in your house is poor and the pedal you're using is poorly designed in terms of ground noise. For instance, your pedal's only grounding source is your guitar cable.
It's more common that dealing with the grounding circuit your amp plugs into will eliminate ground buzz rather than your amp being the culprit.
More often than any other reason, the ground wire doesn't have the capacitance to bleed off the sewage signals well enough for pure silence.

I run through several different amps, all overdriven through an overdrive I designed/built myself from the ground up.
I power my amps with an industrial voltage regulator, fed into a power conditioner then to the amps. Even bypassed and plugged directly into the wall, I get ZERO ground buzz with my hands not touching any metal on the guitar which is due to the overdrive's design and an efficient grounding system.
So I urge everyone, look more into your home wiring rather than fussing with your amp, this is something basically any studio engineer will tell you. I'm no newb to amp mods and repairs and the star ground is rarely effective on anything other than amps built 25+ years ago when the engineering had a much greater level of imperfection. If it comes down to it, wire a dedicated ground from your sink to your amps ground plug. While your water lines will often serve as the ground for every socket in the house, a dedicated line can sometimes eliminate an unknown source of noise in your house that might be your refrigerator or water heater.
It's like grounding a car stereo system, you move it's ground as far away as you possibly can from other grounded devices that cause noise.



ekp

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Re: Grounding techniques
« Reply #11 on: July 15, 2010, 05:13:13 PM »
Since this is about hum as well, another consideration is the layout.  The magentic field from the power transformer and reachout and inject a signal into sensitive circuits.  Physics, you know.  A loop of wire produces a voltage according to the change in field strength.  So one needs to distance high current signals from sensitive circuits, and make the areas in the circuit loops small, even if a bit inconvenient.  There are a couple of ways of keeping loops small.  If it is in wire, there is twisting them.  Each half twist helps cancel the one next to it.  In circuit layouts, there is the possibility of a figure 8 loop between the signal and ground...  That also helps to not pick up other stray signals.

Have a great day, Eric

xiaofang

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Re: Grounding techniques
« Reply #12 on: November 03, 2010, 05:25:34 AM »
The essential part is to start treating the grounding as a part of the circuit itself: Each time a part of your circuit makes a connection to common it will not have a reference of ideal zero volts. Instead, this connection is just the other end of conductor connected to the only real common point that can exist in the system - a conductor with resistance. Since the circuit stage’s current goes through this resistor, then according to U=IR the "common reference" point of the stage must have a voltage potential. It would be better to refer to these points as “common returns” not as commons.
« Last Edit: November 03, 2010, 08:10:34 AM by joecool85 »

bry melvin

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Re: Grounding techniques
« Reply #13 on: November 03, 2010, 03:50:09 PM »
Quote
If it comes down to it, wire a dedicated ground from your sink to your amps ground plug. While your water lines will often serve as the ground for every socket in the house, a dedicated line can sometimes eliminate an unknown source of noise in your house that might be your refrigerator or water heater.

Grounding at the sink is obsolete and useless in most modern housing. Metal plumbing is only used in a few areas (at least in the US) by code.

If you own your own property you can  add a ground to the earth with copper rod Newer code usually requires this at the electrical box, but one can be added grounding your studio filtered ac

Also CFR lighting is a disaster for studios. LOTS of emissions

In modern buildings power conditioning is almost a necessity for the studio. This can be coupled with large ups units that use transformers and MOVs for digital equipment protection. If you are NOT on the grid...solar etc it can get even more complicated as many inverters are not up to running musical equipment. They can actually damage some switching supplies.


Kaz Kylheku

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Re: Grounding techniques
« Reply #14 on: October 09, 2012, 03:31:15 PM »
Should we worry about star grounding in some line-level audio equipment that doesn't produce high output currents?  Like some equalizer box or preamp or whatever.  Say it's made up half a dozen dual op-amp chips, all dual-supply, which are mostly at unity gain or very modest gain.  It's convenient to just run a single ground trace reaching all the places on the board which need a ground.
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