Electric Guitar hum problem

[Old Sparky]

Having recently corrected a wiring fault and re-soldered some poor earth connections on an electric guitar, it's owner tells me that some hum is present, when the guitar is connected to his amplifier.  This wasn't present at an audible level when I plugged it into a small mono test amplifier.  Over recent years I've repaired several guitars which have had various faults in the wiring to the control panels, all of which make use of the pot. bodies as earthing points, and I've suggested that things might be better if the controls were mounted on a suitable metal panel, and various earth leads, including the screens of pickup leads connected, as far as practicable, to one point, the metal pot. bodies being earthed via their fixing nuts.  Has anyone wired guitar controls in this way, and /or found a way to eliminate or reduce hum, which, IMHO, might be caused by earth loops.  I didn't take any pictures of the guitar in question, so cannot post illustrations. (Apologies for that omission!)

[valves4amps]

The problem may not be with the guitar but with the guitar/amplifier/ lead combination.  I have found over the years that some guitarists new to them don't realise that the pickups are sensitive to the magnetic fields from the mains transformer, so orientation and distance play a part.  The lead itself may be worn i.e. Crushed in places where the screen is ineffective.  Valve amp transformers are notorious for this effect and they should be at least 6 feet or more away.

Dave.

[Murphyv310]

Hi.
I'd agree with Dave here plus it might be an idea to check the pickup earthing, jack sockets for condition and wear.
On occasions I've had to jump in the van and go to the venue and see if the problem is due to location. One such visit saw earth connections missing from extensions, screened leads running alongside mains cables and additional screened lead extensions to the amp.
Many musicians tend to leave repairs to the last minute so jobs are often rushed or they forget to bring the whole lot including the amplifier.
Perhaps in this instance ask the customer to bring all his gear including extensions and anything that is connected to the amp that could be a source of hum, the problem may not be the guitar but any other add-on.

[Old Sparky]

The guitar's owner has been playing and collecting guitars for a good few years, so should be aware of the problems mentioned by both of you in the above posts, but I will check with him regarding extension leads, amps., etc. In this case I know the jack on the guitar is O.K., as iI checked it when carrying out the repair. The pickup earthing will be checked when next I see him, so it seems there are several possibilities, some of which hadn't occurred to me (I'm not a musician) to consider before thinking of rebuilding the controls on a metal 'chassis'

[Murphyv310]

There shouldn't be any need to rebuild the controls. If it worked fine for many years why would you need to modify the existing arrangement? The only way something has changed is a fault IMHO.

[Old Sparky]

I'm not sure if they worked for 'many years, Trevor'. The owner, who by his own admission, isn't an electronics technician, builds control circuits from descriptions in books and on-line. Several times in the past I've repaired guitar control circuits for him, and all have been 'hard wired' in the same way.

[Murphyv310]

That though is the way they are done on many guitars both cheap and some of the best like Gibsons etc.
One problematic guitar I had with hum I decided to relocate the pots onto a plate rather than its poor quality plastic mounting plate to find it was a waste of time. Turned out to be a hum loop elsewhere, wrongly wired internal preamp from new.

[BusyBee]

Wasn't this one of the reasons for developing humbucking pickups? It would be useful to try more than one guitar in the amplifier, and connecting lead too. I think guitar amplifiers has things like prescence controls etc which when turned up provoke hum pickup and put the guitar on the point of feedback, although the user would likely be aware of this. If the guitar was initially faulty though it may not have been obvious.

Tracy

[Murphyv310]

Hi.
When we had the audio workshop at Clydesdale in Kilmarnock we insisted that the customer brought in everything not just what he or she perceived was the faulty item, it reduced agro and possible bouncers.