Massive Hum

[StratDudeDan]

first of all, my schematics are here:

http://fullservesite.com/stratomagic/stuff/untitled

situation:

two single coil pickups (one the neck, one mid from a strat) are wired in parallel to a volume pot, which runs to a capacitor.

problem:

there is a huge amount of hum and noise while i'm playing, and when i'm not touching the bridge or strings, the hum increases by about 10-fold. yes, everything is grounded. yes it's soldered and not twisted. i even went as far as soldering a wire directly to the back of the bridge and then to the jack plate, yet the hum persisted. it's 60-cycle which makes me believe it is ground related, but i don't know how that's possible.

question #1:

is there something inherently wrong with my wiring diagram. i seems to be frighteningly similar to the schematics for the Tom Delonge strat (he has the cap wired across the input of the jack to the wiper, instead of after the wiper in-line), so i assumed not.

question 2:

if there is, what can i do to fix it?

question 3:

if not, what could be creating this? i read something about a ground loop somewhere that could create hum. could this mean that my two pups have a vastly different impedance? i don't have a working multi-meter, so i haven't checked that yet, but is that still a good candidate?

question 4:

if it is at fault of a ground loop, how would i fix it? could i just stick a resister in series with the lesser impedance line to "balance" it out? is there a way to wire it in series to create only one path to ground that would work?

thank you in advance!

[Guitarfrenzy]

First off, I would definitely check to make sure that your input jack wires aren't reversed, that alone can produce massive noise and hum. See if they aren't switched. The middle lead on the volume pot should be wired to the tip of the input jack and ground to sleeve. Also, check to make sure each pickup is grounded the same place as everything else. In most cases, your gonna solder the two black wires coming from your pickups to the back of your volume pot, then you also need a ground from there to the tremelo spring claw and input jack sleeve. If you have more than one pot, then your gonna want to solder a wire that jumpers each one so that they all have a common ground. Also, shielding paint helps a lot in cavities and if using a pickguard, get one with shielding on the back of it. The one thing you must do is get all your ground wires connected to a common place, that means that all grounds should display no resistance if ohmed, they should in fact read 0 ohms if compared. If they don't, then you really don't have a common ground and will guarantee problems. With an ohm meter you should really be able to nail down the problem, check your pot to see if it's working correctly, and each pickup to see if the resistance is correct. Your capacitor also might be a problem, so basically check for everything.. lol

[Southpa]

I always double check my wiring and grounds for continuity with a multimeter. The end of your amp lead is 3 parts, the ground sleeve, the little black insulator ring and the hot tip. So check for ground continuity by touching one end of the ohm meter to the sleeve and the other end to all your ground points inside the guitar. Then check all your "hot" points by bridging the tip of the amp lead and switch/pot connections. Move the switch to different positions to make sure it isn't wired bass-ackwards and turn volume and tone controls to see if there is variable resistance.

[lovekraft]

What's the cap for? As wired, all it does is cut low end as you turn down the volume pot, so you lose lows and highs along with lowering the volume. Try it without the cap once, just to see if it's "enhancing" the hum (a 250K pot and a .01uF cap have a corner frequency of around 63 Hz, depending on tolerances).

[Saber]

(a 250K pot and a .01uF cap have a corner frequency of around 63 Hz, depending on tolerances).

You also have to consider the input impedance that your driving. If it's a guitar amp with a typical input impedance of 1M, the cutoff frequency is closer to 16Hz. So there really isn't much point in having that capacitor there since it may contribute some noise without any benefit. If you really want to cut the lows a bit, it would make more sense to place that capacitor between the pickups and the clockwise leg of the pot for slightly more consistent results into different input impedances.

[Saber]

BTW, are the pickups connected in phase or out of phase? That could explain why hum would be much louder than the string signal. Since they're neck and mid pickups from a strat, I assume they're magnetically out of phase, but did you connect them with the proper phase relation.

Edited November 4, 2004 by Saber

[StratDudeDan]

yes, the lead and ground wires were connected to the jack correctly.

as for the proper phase relation, i'll be honest in saying i don't know...

right now they're wired with both leads as their "hot" side and the grounds to ground. if i need to change this, no problem.

as for the cap, easy to pull out (as i'm re-wiring the whole thing again soon...), and if i were to need it back, i was going to run it from the input side of the pot to the wiper, like is done in the Tom Delonge strat. so it's no problem to pull it out and screw around with that.

[Paul Marossy]

I won't claim to be an expert in this, but usually, a hum from hell comes from a bad ground or something that should be connected to ground, but isn't...

Have you:

Checked all of your solder joints?

Determined that your pickups aren't faulty?

Connected the bridge to ground?

Shielded the guitar properly?

Determined if it still does it if you physically move the guitar to another area?

Just my thoughts on the possibilities...

[StratDudeDan]

1 Checked all of your solder joints?

2 Determined that your pickups aren't faulty?

3 Connected the bridge to ground?

4 Shielded the guitar properly?

5 Determined if it still does it if you physically move the guitar to another area?

1 yes

2 not sure how i would do this, but i've never had any problem with them in the past

3 yes, in more ways than most people could have imagined

4 yes. there's a shield over the entire pickgaurd as well as the back of the rout in the body. not on the sides, but as i said w/ 2, i've never had an issue with this body or pickgaurd before.

5 if i'm about 2-3 feet away from the amp, the hum goes away. i tried it in another room (my practice room tends to be noisy, flourescents as well as iffy power), and it still hummed, though a wee bit less (nothing major, just noticable).

thank you for the suggestions, though.

[Paul Marossy]

if i'm about 2-3 feet away from the amp, the hum goes away. i tried it in another room (my practice room tends to be noisy, flourescents as well as iffy power), and it still hummed, though a wee bit less (nothing major, just noticable).

Well, that explains a lot. If you are close to the amp, you will pickup hum from the power transformer in the amp. And, if they are single coils, you will always have a small amount of hum no matter what you do. Humbuckers work better in these situations, hence the name "humbucker".

EDIT: Other sources of hum can be computer power supply fans, computer monitors, doorbell transformers and motors.

Edited November 4, 2004 by Paul Marossy