Eliminating guitar hum

[Radardoug]

Cavity sheilding is very important and usually not done. Pickups often have no sheilding on the wires coming of the pickup either. If you do this you will reduce all the extraneous noise pickup, but the pickup will still pick up noise. But you do reduce the amount of pickup significantly. Then find the null position in your room.

[enginefire]

the cavity is well shielded, i did it personally a few years ago.

I will add some wire mesh attached to ground on one end to the wires that extend from the pickups and add some copper foil to the inside of the pickup covers to complete the job... after that i guess its on to experimentation with inductors and dummy coils.

[Radardoug]

I have used another non-humbucking pickup as a hum canceller in temporary situations. Just wire it in parallel with the internal pickup, find a place on the guitar body where it cancels, and gaffer tape it to the guitar! Crude but effective.

[enginefire]

here is my solution, I now have a dead silent telecaster with an awesome meaty tone! the red jumper wire that is glowing is the magic, without that its pure noise.

[Radardoug]

Ah! So basically you are earthing the guitar! Also to note, that 20K to 600 ohm transformer will be drastically altering your tone by loading the pickups. Any of the purists out there like to comment?
But hey, if its clean and you like the sound, go for it!

[enginefire]

There is a definite improvement in tone! thicker and the high end seems sweeter. I will post some samples, with and without the earther unit.

What would the pickups normally like to see as input impedance? something higher like 50 or 100k? it tele is using 500k pots. the SG epiphone also sounds great through it. I still want to test it with a big muff in front to see how it reacts.

[LeeYoo]

Hi enginefire.

The guitar cable capacitance sets the resonance/cutoff frequency.
Thin/long cable = lower peaking frequency.

The resistive load sets the dampening of that frequency.
+/- 100kohm is a flat response.

Depending on the pickups.

Some guitar amps had two inputs.
Hi was 1 megohm.
Lo was 136 kohm (2x68k in series).

http://www.buildyourguitar.com/resou...emme/index.htm

Leo..

[Radardoug]

To have minimum loading effect the guitar should be loaded with about 10 times its impedance as a rough rule of thumb. So in this case with 500K pots, you should load with no less than 5 megohms. However as Lee Yoo said, a lot of guitar amps are 1 megohm input, and the cable capacitance has a significant loading effect. Your d.i. at 20,000 ohms is way low. But when I look at that tranny again I see it is rated for restricted frequency response as well!

As I said previously, if it sounds good, use it, but from all engineering aspects it is badly matched.

[enginefire]

I noticed the frequency response after I bought it... I figured for guitar or bass it would be fine, if the top end is rolled off so be it, it still sounds good then even better for guitar imho.

i didnt really think about the input impedance, i figured 20k would be hi Z.

Would adding a large resistor (100k or 1meg or more) in series with the signal wire and trafo input help to reflect a better load to the guitar?

[enginefire]

the secondary is attached to a balanced mic input on a preamp and then into the balanced mic input on a console. I dont know the specs off hand, but safe to say that they are designed to work with the 600ohm standard.

[Radardoug]

Putting a resistor in series will introduce a lot of loss, and may affect the frequency response badly.
If it sounds good as it is, just use it and don't worry about it. You aren't going to blow anything up.

[ripgtr]

The eternal single coil issue.

1. Sheilding helps. However, you have to sheild the pickups too, inside the pickup covers. I did that once, pain in the butt. SRV supposedly did that. It is said to effect the tone somewhat.

2. Humbuckers buck hum, by putting two coils near each other and putting them to opposite polarity. This also bucks some of the tone. Humbuckers do not sound like single coils. Whether you notice, care or prefer one or the other is preference.

3. Noiseless pickups - supposedly some of the newer ones sound the "same" as single coil pickups. Lace, Bartollini, emg, all the ones I tried back in the 90s did not. Again, you might prefer them.

4. Dummy coil - the same idea as humbuckers, but with the coil further from the strings, so the noise that comes from far away is cancelled but the string sound isn't. Works pretty good. I have one that goes on instead of the back plate on a strat, this seems to work pretty good.

5. Except that you have to move around away from noise sources or change your angle to the source. Amp transformers, computer monitors (CRTs are the worst), etc etc. Usually you can find a place where the hum is less, and you stay at that angle.

There is no perfect solution. I accept that there is going to be some noise because to me (and this is HIGHLY subjective) single coils sound better, at least for ME playing and getting what I want. Though I do have buckers and have used them, as well.

[LeeYoo]

If you pick up the crap with a seperate coil and amplify/buffer that signal, you can insert that with a lower impedance, e.g in the ground line.
It will have less impact on the rest of the guitar circuitry and sound.
Leo..

[JohnRoberts]

Originally Posted by LeeYoo

If you pick up the crap with a seperate coil and amplify/buffer that signal, you can insert that with a lower impedance, e.g in the ground line.
It will have less impact on the rest of the guitar circuitry and sound.
Leo..

This is 6 of one, half dozen the other,,, subtracting the anti-hum signal from the hot or opposite polarity from the ground will be similar. It needs to be injected at roughly 100% to cancel the hum, so same-same impact for noise and all.

There may be problems with alternate ground connections, but guitars are generally floating.

JR

[billkahler]

Shielding in my tele and my strat knocked the hum down 90 - 95%. Huge difference.

[LeeYoo]

Originally Posted by JohnRoberts

This is 6 of one, half dozen the other,,, subtracting the anti-hum signal from the hot or opposite polarity from the ground will be similar. It needs to be injected at roughly 100% to cancel the hum, so same-same impact for noise and all.

There may be problems with alternate ground connections, but guitars are generally floating.

JR

Hi John.
True, hum and buzz must be of the same amplitude and 180 degrees out of phase with the instrument's hum and buzz.
My point is that if that signal is buffered, you can inject it with less impact on the instrument's sound.
e.g. injecting it with a 100meg resistor on the "hot" terminal after voltage amplification, or injecting it over a 100ohm resistor in the ground line after current amplification.
The circuit could be battery powered (floating) and referred to the guitar's ground.
Leo..

[Jim Williams]

I use a 1" square double sided pcb mounted with a dual opamp. 1/2 is the signal preamp, the other 1/2 does phase reverse cancellation, pre-conditioned to remove those hum harmonics, 60, 120, 183, 250 hz.

That feeds a trimpot. Rotate it and all the hum drops off, to about -80 dbu.
I use an import plastic strat bobbin removed of all metal for the dummy coil, the closer it matches, the deeper the hum null.

I use original 1960's era Fender Tele pickups, with a -80 dbu s/n ratio, not too shabby.

Everything is screened and the pickups are shock mounted. I play on "11" but have no noise and complete stability, tough with a Telecaster. I do Hendrix like controlled feedback, but on a Telecaster. Yes, it can be done, it's been done here for over 20 years.