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Old 2nd March 2014, 06:40 PM   #11
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Join Date: Dec 2012
Location: Athens
Originally Posted by nigelwright7557 View Post
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.
Yes, but I would say that if you see that as common practice in already delivered guitars, you can't just assume it is good practice. Open up a Fender amp - it sounds wonderful, but be prepared not to encounter the rules you follow for your power amps.

A tiny current says nothing to me. You plug the guitar into really high impedances, you amplify millivolts. Even microvolts of anplified noise can be heard. Use a Big Muff, or any other high-gain device. Total gain could be as high as 500 times. Account for another 60-70 times for the first amp stage. Do you still think that a small current can't harm? I don't.

As a matter of fact, usually (and crudely, I don't do that) single-coil players don't use huge gains to shape the tone. So they bear with noise they could get rid of, since it is small. In other words, you don't play metal with single coils. These players use humbuckers and huge gains - different field. I am suggesting that in the guitar world, bad practices have gone all along their way since everyone could bear with them. They were not correct practices - they were acceptable.

I personally choose not to go with acceptable, rather with correct.

Correct could save me in the future. As you said, you did not apply star ground to your amp and voila, hum. I have also done that. So, the way I see it, it is very important to start thinking the right way early on, it will save you time.
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Old 2nd March 2014, 06:43 PM   #12
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Join Date: Apr 2008
Location: Carlisle, England
There was thing at one time to put buffers in guitars.
This reduced the output impedance and helped driving into screened leads.
The only down side was you needed a battery in the guitar.
Murton-Pike Systems PCBCAD51 pcb design software.
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Old 3rd March 2014, 12:52 AM   #13
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Join Date: Oct 2013
Thumbs up Star grounding.


audiostrat. I agree with your point(s) about the importance of star grounding. Very good point about post-guitar gain stages increasing minor hum to excess. One thing that irks me however, is the fact that often guitars have so little extra room in the control cavity for doing much of anything. I have learned(the hard way) that when purchasing any guitar or bass, it pays to insist upon inspecting "under the hood". I have an Ibanez bass that you couldn't add a capacitor for lack of room in it's control cavity ! Any opinions on how effective conductive paint is for shielding. I am sure that copper foil is probably better, but it also is a pain in the butt to use.

Thanks to all who have replied to my post. Most Sincerely, tonequester.
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Old 3rd March 2014, 09:01 AM   #14
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Join Date: Dec 2012
Location: Athens
You can also star ground everything on the back of a pot, and then move a wire from that point to the jack. That would require less space anyway.

My guitar cavity is shielded with conductive paint and I must say that the result is pretty good. I remember having more noise (high-pitch crackles etc) without it, so I would say it is a good addition. Copper should be better indeed, but I wouldn't lose my sleep over not having it. Having said that, I plan to add copper sometime. But paint does its job for sure.
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Old 3rd March 2014, 07:09 PM   #15
DF96 is offline DF96  England
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Join Date: May 2007
Originally Posted by Enzo
Remember that a ground loop is a condition, not a thing.
Not quite. A ground loop is a thing, which may have a condition.

The thing is a loop of conductors, enclosing an area. This may pick up stray AC magnetic fields.

The condition occurs if the thing has currents sent to it or induced into it.

Without the condition you have no problem. Without the thing you cannot have the condition. Hence get rid of the thing and you cannot have the problem.
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