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Old 11th January 2014, 12:23 AM   #1
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Smile Proper Grounding of Potentiometers, Volume and tone control, electric guitar.

Greetings. This may not be the right place for this post, but I was unsure where else to go !

I need some opinions on proper grounding. On an electric guitar such as mine, there is one volume control, and two tone controls that affect different pickups and combinations of them. I have always read that one should beware of ground loops, that all grounds should be made to a common "point". that ground loops act like an antenna, and pick up noise from external sources like transformers. However, when I get component parts, like the blender pot that I am getting ready to install, inevitably their diagrams show the pots being connected by wire, from the back of one pot to the back of another, so all three would be connected this way on my guitar. This despite the fact that all pots are grounded to the shielding foil, which is on the under side of the pickguard. Would not this constitute ground looping ? Once again, all pots are connected to ground by their very installation on the pickguard. ???????

Thanks to anyone who would take time to give me their opinions, on such an elementary topic, yet one that has me perplexed......tonequester.

Last edited by tonequester; 11th January 2014 at 12:24 AM. Reason: forgot to mention....
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Old 11th January 2014, 12:52 AM   #2
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Star grounding is usually used in amplifiers.
A problem that can occur is charging pulses into smoothing capacitors modulating the ground line and causing hum.
Or higher power level in the output stages of an amplifier modulating ground.

This doesn't apply in your electric guitar as there is no serious current flowing.
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Old 11th January 2014, 03:26 AM   #3
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Greetings, and thanks for the reply nigelwright7557.

I appreciate your clarification my friend. It makes sense to me that due to the small signal strength in an electric, it might be advisable to be redundant with your grounding, instead of trying to worry about getting rid of every ground loop.

Many thanks, and hopes that all is well for you in Carlisle, England. Now I must Google Carlisle, England to keep my geography sharp. I always check to see how close English towns are to Liverpool,because my whole music experience began "With the Beatles". I actually watched them on the Ed Sullivan show, Feb, 1964. Now you know how damned old I AM !
Sincerely, thanks for the help ! tonequester.
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Old 11th January 2014, 04:48 AM   #4
Enzo is offline Enzo  United States
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Remember that a ground loop is a condition, not a thing. A ground loop occurs when there are currents flowing between ground sections of a circuit. A common example is connecting two pieces of gear together with a signal cable, and the two pieces happen to have slightly different chassis potential. Current flows between them, and causes the loop.

Other than the micro or pico amps of signal current within your guitar, there are no power returns or any of the other stuff found in the amplifier inside your guitar.

While it is common for the mounting bushing of a pot to be electrically connected to the rear cover of the pot, it is not always. So we sand a spot on the pot backside, solder a ground wire to it, and we are then assured of a good ground connection.
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Old 12th January 2014, 07:13 PM   #5
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Default Proper grounding of pots.

Greetings Enzo.

Thanks for the info. CONDITION not a thing....I get that. I guess some of the "guidelines" I have picked up in a general electronics way, don't always apply to the small signal/current of an electric guitar.

In putting this midrange control together, I used a blender pot from Stew Mac, used to blend pickups. It does not have a metal back. I soldered the cap and inductor leads, each to one of the source terminals on the pot, and then soldered the other ends to the SIDES of the pot. When I check(continuity) between the pots sides, and the ground wire(to go to common ground), I get zero Ohms at full counter clockwise, and 500k at full clockwise, so I guess that ground wise, it's O.K. Otherwise, of the 6 terminals, 2 pairs are jumpered, and then you have an output terminal.

Although the pots ground to the shielding foil on the back of the pick guard. The pot has a ground terminal, that I have wired to go to the common ground on the copper foil tape I have lined the cavity with. Do you guys think that I should then go ahead and connect all three pots as well ?

This is the kind of mod that I pretty much have to install and play, just to tell if it is going to work at all(at least with my limited knowledge, and test equipment). I'm trying to cover all bases, as best I can BEFORE "stringing it up" ! I DO realize that it might sound like sh--, but it's not just about tone here. There is the learning experience, plus keeping my assembly/ soldering skills at a level of good quality as well. That's why I just didn't order Rothstein's mod, which looks to be much better than the Torres model, and is less than $50.00. I don't know if I buy into their hype about the Orange Drop cap used. But other than that, my "design" should be comparable, right down to the center detent pot that they claim is an exclusive of theirs.

Thanks to Enzo and nigelwright7557 for your input. If you have any other tips, advice, or opinions, they are most welcome ! Best Regards....tonequester.
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Old 2nd March 2014, 06:48 PM   #6
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Quote:
Originally Posted by nigelwright7557 View Post
Star grounding is usually used in amplifiers.
A problem that can occur is charging pulses into smoothing capacitors modulating the ground line and causing hum.
Or higher power level in the output stages of an amplifier modulating ground.

This doesn't apply in your electric guitar as there is no serious current flowing.
I am afraid that this is bad practice.

You are suggesting that not properly grounding a guitar may not bring up serious or noticeable problems. This may be true. Even if it is true, it is bad practice not to implement everything carefully, escpecially considering the labour needed - it is ridiculously simple to star-ground a guitar, why not do it?

If you form a ground loop, this loop will be susceptible to external noise and interference, since a current will flow within that loop, creating a corresponding voltage which will be amplified afterwards. You are talking about small currents, but may I remind you that the effects pedals that may follow and the amp itself can have enormous amounts of gain available. Based on your avatar picture, I bet (hope) you know about all that anyway.

My advice would be to implement star ground. In my opinion, is it nonsense not to do it, given its simplicity, cost (zero) and the fact that after all, it can't harm.
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Old 2nd March 2014, 06:51 PM   #7
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I wasn't suggesting you shouldnt ground everything.

My point was more from my amplifier design experience where significant current causes problems in ground lines. I have seen volts of ground modulation.

In a guitar pickup it is a very small current so the effect wont be as big as in an amplifier.

I have seen some guitars with metal screening panels in them which are grounded to reduce hum.
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Old 2nd March 2014, 07:09 PM   #8
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Quote:
Originally Posted by nigelwright7557 View Post
I wasn't suggesting you shouldnt ground everything.

My point was more from my amplifier design experience where significant current causes problems in ground lines. I have seen volts of ground modulation.

In a guitar pickup it is a very small current so the effect wont be as big as in an amplifier.

I have seen some guitars with metal screening panels in them which are grounded to reduce hum.
I didn't say that you suggested not to ground everything - I said that you suggested that star-grounding is not necessary at all. Which you did, if I understand English well. :

I also use shielding in my guitar, and it helps with noise, escpecially high-frequency since the metal used can't be thick enough or steel. But this is indeed an amelioration. Saying amelioration, I suggest that one should verify at the first place that its circuit is properly designed to reject noise as a topology, and afterwards working to further improve matters by taking additional steps. Including a mistake in the design (mistake in my opinion anyway) does not fall into any of these categories and should be immediately discarded.

May I also suggest that sometimes people asking such things may lack experience and it should be beneficial for them to learn how to implement things right early on, on such easy projects. I have been there, actually, and I am not claiming myself to be experienced at all.

EDIT: What is more, if you create a ground loop, you can't talk about guitar pickup signals any more - the noise voltage will not come from them, but will solely depend on the resistance of the loop.

Last edited by audiostrat; 2nd March 2014 at 07:11 PM.
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Old 2nd March 2014, 07:18 PM   #9
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Interesting...

I'm wondering if the OP could post a pic & layout, schematic
of his axe.

There are pro's and con's to the grounding methods.
They all can have problems.
I've seen star grounds, buss grounds, Ill call it
island grounds, plane grounds have some serious problems.

My thoughts are grounding is probably more important in this
small signal guitar pick ups than hi power amps in that any
miniscule problem in a guitar (as source) will then be amplified
100's or 1,000's of times in the amp.

I've found it also beneficial to use very high quality componants,
pots, wiring, caps, solder, etc. Again this is small signal generation
and the basis for your tone.

Do not over look the guitar's mechanicals either.

What pick ups are we using? single coils or humbuckers?
In what type of guitar? Hollow body, semi hollow body,
or solid body?

Is the current wiring sheielded?

Anyone whos played guitar knows that there are various sources
of RF noise that create havoc, from floursents, LEDs, and even worse
Neon lighting (esp in clubs).

Yes avoid LOOPS,

AND

Keeping just one long ground string is what you want
for all parts of the chain.

Don't forget to make sure you have a good stout grounded jack
in your guitar that is grounded also.

Kind of what Enzo, Audiostrat are saying,
also do some research and try different things,
try to gain experience and knowledge, which you are doing. ; )
__________________
-- Sync

Last edited by SyncTronX; 2nd March 2014 at 07:37 PM.
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Old 2nd March 2014, 07:24 PM   #10
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Quote:
Originally Posted by SyncTronX View Post
Interesting...

Keeping just one long ground string is what you want.
. ; )
This is what I have seen in a couple of guitars I have had.
This is what my point was, there is very little current in a guitar pickup.

I once designed a mixer and when the pcb was built up hum was massive.
I had not star grounded the power supply and there was 1 volt of hum on the output op amp !!
I redid the pcb with star ground and ground plane and the hum was almost zero.

I have designed a few class d amps and they were very fussy about grounding.
When the output transistors are passing 10 amps the ground line gets seriously modulated.

Its not just star grounding but keeping tracks as short as possible and things need to be well decoupled.

Last edited by nigelwright7557; 2nd March 2014 at 07:29 PM.
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