New electronics for electric

[DHopkins]

I have a solid-body f-style electric made by (now deceased) Mac McCormick in Columbus, GA. I havek a frequently-occurring hum. I've grounded everything in every way I know how but the problem persists. I want to change out the electronics with all new.

It has a Telecaster-style pickup. Originally, Mac had a lipstick pickup in the flat triangle cut-out. I replaced it with a Seymour-Duncan mandolin pickup that was made in the Telecaster style to fit the opening. It has 500k pots (tone & volume). Would there be an advantage (or disadvantage) to using 250k pots?

[pops1]

500k pots are usually used for humbucking pickups and 250k for single coils. The tele would be a single coil. Either will work, but you will have sound differences. Have you grounded your tailpiece? That can be a source of buzz. Also single coil pickups can pickup things and buzz, does it change if you turn the mandolin?

[DHopkins]

Pops1, I have grounded the tailpiece but that doesn't seem to help. I may scrape the finish where the ground wire makes contact in case there some sort of "clear coat" finish on it preventing contact to metal. I don't know where the tailpiece came from. It was on the mandolin when I bought it several years ago. Also, the hum is constant regardless of instrument orientation. It increases in volume as I turn up the volume. I would look for cold solder joints but if I'm gonna change the pots, I might as well wait and do the inspection once I get them installed.

[pops1]

So you have good grounds to all the pots, jack, switch (if you have one),tailpiece. Have you shielded the cavity at all. It's not always necessary, but sometimes. Does it make a difference in volume of buzz when you touch the strings or not touch them?

[DHopkins]

I thought I had good grounds throughout but apparently that's not the case. Incidentally, no switch and the cavity is shielded and grounded, including the cover. Touching the strings makes a difference.

[Marty Jacobson]

Can you describe how it's humming?
For example, in my house, all my guitars hum. It's because I have modern WiFi and LED and fluorescent lights, and it's no the guitar's fault. It's the player's body acting as an antenna, and only if I ground myself to the string ground does the buzz go away. A lot of players use wrist straps or other grounding solutions in studios because of this. Also, have you tried your amp with another instrument to confirm that the hum is indeed the instrument's fault?

[pops1]

Try putting a ground wire temporarily to the strings, sounds like the ground to the tailpiece is not the best. As Marty says a lot of things in the home cause hum. Plugging into the same circuit as a florescent light will do it. Have you tried another room or location.

[DHopkins]

First of all, I misspoke. Touching the strings makes no difference. Turning up the volume on mandolin or the amplifier increases the hum. It is a hum and not a buzz. It hums on a Behringer 15W amp and a Roland 90W amp. A couple of weeks ago, I hooked it up to the band's mixer and, of course, it hummed.

I do have fluorescent and LED lights. I turned them off with no change. I've decided it is the mandolin and not an external source. I think I will replace the wiring with a new harness (250K pots). If that doesn't work, it will become a nice wall hanging because the workmanship is great. It looks good but it just doesn't sound good right now.

[Bill McCall]

There’s a good troubleshooting section at Lindy Fralin, at least to me. Their discussion of grounding my be relevant to you, especially ground loops.

[pops1]

Can you take a pic of the wiring?

[DHopkins]

The green wire trailing off is a ground wire I specifically (and temporarily) attached to the tailpiece to assure it was grounded. It didn't work.

This wiring was done by a regional luthier about 3 years ago.

[rockies]

If the hum occurred after installing the Seymour Duncan try reversing the leads.
Dave

[DHopkins]

If the hum occurred after installing the Seymour Duncan try reversing the leads.
Dave

I'll try that.

I went to the Fralin website and the problem might just be the fact that it's a single coil pickup. He says they all hum.

I should've mentioned that I'm not terribly familiar with pickups. This mandolin and my lap steel are the only instruments I have with this type of pickup. The lap steel is factory-made and I've had no trouble with it.

[pops1]

You have a black wire for ground on the upper pot and a white wire for ground on the lower pot. It's hard to see where all the wires go, but if black is ground, black is ground and the white wire should not be grounded to the pot. You also have a bare wire for ground, which is common to do. On the jack you have black, white and green. You said the green is for grounding the tailpiece, but it should come from the same place as either the black or white which ever is ground. Seeing as you have both grounded to the pots it is hard to tell which is ground.

[rcc56]

Do you get any signal at all or do you only get a hum?

A loud hum usually indicates an open circuit or miswiring. Open circuits can be due to broken or pinched wires and cold solder joints. But . . .

I can't see where everything goes in your picture, but I agree with Pops. "Something don't look exactly right." The more that I look at this, the more I am convinced that it is miswired in more than one place.

Double check your wiring against a good diagram. And be careful of that bare wire between the cases of the two pots. Make sure it is not touching any of the contacts on either pot.

When all else fails, have somebody else check your wiring for you. Some of the connection points are covered up by the wires in your pictures and we can't see for sure what is going on.

[Tavy]

Unfortunately, there are lots of causes of hum:

* Single coils - yes they will hum to some degree, but it shouldn't be really bad.
* Something not earthed: take a multimeter and check that everything that should be earthed really is.
* Dry solder joint: hard to diagnose, but I don't see anything obvious in your image.
* Ground loop: over-enthusiastic earthing can lead to loops - everything that is earthed should have one and exactly one route to earth. 2 routes to earth == ground loop == hum. You have to trace the circuit to check this.
* The strings: the strings act as an antenna and will pick up the computer, the WiFi and everything else in the room. Not normally an issue on mandolins - the strings are too short - but for longer scale instruments it can be a real issue. Try moving the instrument to different locations (and change it's inclination - up, down, flat etc) and see if the hum changes. If the hum changes with position it's likely acting as an antenna.
* The household wiring: if the problem goes away when you touch the ground on the amp, then the issue may be with your local wiring (or the amp) rather than the instrument.

[Marty Jacobson]

Is the leg of the capacitor soldered on to the top of the tone potentiometer? If there are things grounded which shouldn't be, as John and others have said, you will definitely get hum (as well as loss of tone, probably loss of function of the knobs).



This is the wiring diagram you need:

[Bill McCall]

Maybe it’s time for square 1. Pull out the pots and check the wiring in an uncluttered space against a good diagram.

[pops1]

The tone cap can be grounded to the case, it is done that way in many diagrams. If so you won't ground the lug of the pot, it will still work the same. I think removing all to an open place where you can see what is going on is a good idea.

[DHopkins]

Thanx, guys. I've got some good info. I think I'm gonna start by doing what Bill McCall said and go to square one since I'm gonna change the pots anyway. I'll order them tonight. I have some wiring diagrams and good advice so we'll see what happens.

Incidentally, I'm not a complete neophyte. I do ham radio so I've done some "soldering stuff."

[gspiess]

They do make Noiseless pups for Teles. I don't know if they would work for your application or not.

[DHopkins]

They do make Noiseless pups for Teles. I don't know if they would work for your application or not.

My pickup is Telecaster type. Seymour-Duncan made it for me in the form of a Telecaster pickup but is made for a mandolin and has only 4 poles.

Mac McCormick was a local luthier and specialized in acoustic guitars. He had a 3-year waiting list when he died in 2007. He only made 3 mandolins. I have two. He was mostly experimenting with them, I think, but he still did good work. This is one shot of the back/neck of the electric.