Strange hum problem has me stumped.

[Caddy65]

I am getting some hum when recording. It only happens with a few of my twelve guitars. The odd part is that it is the worst with two of my three humbucker guitars (the other humbucker guitar is quiet), and to lesser extent with a P-90 guitar. It doesn't seem to be the guitars themselves, as they are quiet as can be even with the amp volume and gain turned up full. None of my other guitars, even single coils, have any problem. I only play and record clean and at low levels.

These guitars are, as I said, quiet until I activate the mic. Then I get hum that stops as long as I am contacting the strings, or bridge (even better).

I have tried both condenser mics and dynamic mics, SM-57 and a made in USA Peavey. Happens with all. I am using a Tascam DP-0008, and its phantom power for the condenser mics.

This has me stumped since the guitars that exhibit this are quiet until the mic is activated.

Any thoughts? This is driving me crazy (not a long drive for me).

 

[Chili]

Are you using Batteries, Power Supply or USB power? Try it different ways.

Have you tried different mic cables? Guitar cables?

 

[Caddy65]

The Tascam is using 9 volt adapter (from Tascam). It runs only a very short time on batteries. If it was that it seems it would affect all my guitars, not just a couple.

 

[Chili]

Maybe, but not necessarily. There might be too much of a load with some pickups over others. Or with some mics over others. Still, doesn't hurt to try it with the power supply, does it?

 

[Caddy65]

Just for clarification....

- You're micing the amp. Your guitar is connected to amp, but the mic and DP008 are not connected to the amp in any way.
- Is the amp of a vintage that has a two wire cord and not grounded?
- Does location of the mic, its cable, or the guitar and its cord make any difference?

I had a sort of similar, but different hum problem a few years ago that I don't recall the details of, but it was somehow related to using a USB interface with a mic and that the USB connection didn't provide a good ground for the mic and interface. The audio would have a hum unless I touched the body of the mic or the stand it was on. I kind of "fixed" it by plugging a 1/4" patch cable into the interface and back to a piece of rack gear that I knew was grounded back to the wall outlet. The patch cable did nothing more than provide a ground back to the mic.

Your DP008 with its wallwart isn't really grounded and perhaps some AC is getting coupled through the recorder to the mic and acting as an antenna that some of your guitars might pick up (not all shielding created equally). When you touch the strings or bridge you sort of divert the AC floating around away from the guitar. If you set the guitar down and touch the mic or its XLR connectors does the hum change or go away?
I kind of hesitate to suggest grounding your DP-008 as I don't know what you have for gear that you could do it with. If you have an effects unit or mixer with a 3 wire plug connection, possibly try running a patch cord from its output jack to one of the inputs on the DP-008 to create a ground.

Yes, I am micing the amp. The amp and the Tascam are not connected in any way. They are even on different circuits.

It is a fairly new amp that has a ground. It is a Fender Vibro Champ XD.

I have tried moving the cables around to separate them, to no avail.

This would be easier to figure out if it was happening to all the guitars, not just two. One guitar is a 335 copy and the other is an LP.

I was wondering if the mic cable is picking something up, but why with just two guitars, and those two having humbuckers.

As I said, I am stumped by this and have been recording since 1960 beginning with two track 1/4 tape, and on to a Fostex 4 track cassette recorder and then through a computer interface and the Tascam. I never had this issue at all until a few weeks ago. Worked fine with the Tascam, same mics, guitars, etc. until a few weeks ago.

 

[Chili]

Yes, I am micing the amp.

I'm sorry, I missed this part.

Is it possible to use a different USB port? Different computer?
Disconnect everything else from all other USB ports.
Try a different interface.
Stand away from your computer or turn away.

Buy a circuit checker and verify your wall outlets are wired properly. $3 at any hardware store.

Good luck.

 

[Caddy65]

I'm sorry, I missed this part.

Is it possible to use a different USB port? Different computer?
Disconnect everything else from all other USB ports.
Try a different interface.
Stand away from your computer or turn away.

Buy a circuit checker and verify your wall outlets are wired properly. $3 at any hardware store.

Good luck.

I'm not using any USB port, interface, or the computer.

I have checked the outlets. They are fine. If it was that it should affect all the guitars or the amp, which it doesn't.

 

[ecc83]

" Then I get hum that stops as long as I am contacting the strings, or bridge (even better). "

Those guitars do not have the bridge and therefore the strings bonded to the guitar earth.

Check for continuity from bridge to jack body (I am assuming that you DON'T own twelve guitars and not a $20 digital meter?).

I would also bet those guitars have not been screened internally.

Dave.

 

[mjbphotos]

Does the hum happen if you don't have a mic plugged into the Tascam, but do have it on? If not, we've figured out the mic cable combined with the Tascam circuit is doing it. If yes, then it' smost likely the wallwart - but first just try running the Tascam off of battery and see if the hum still appears.

 

[Caddy65]

" Then I get hum that stops as long as I am contacting the strings, or bridge (even better). "

Those guitars do not have the bridge and therefore the strings bonded to the guitar earth.

Check for continuity from bridge to jack body (I am assuming that you DON'T own twelve guitars and not a $20 digital meter?).

I would also bet those guitars have not been screened internally.

Dave.

Actually I do have a meter, a $500 Fluke meter I used for work until I retired. I have rewired nearly all my guitars and have checked the circuits and all connections on these two guitars. They are fine. I have also checked the outlets for polarity and ground those are also fine. I have tried using a different circuit for the amp than the one the Tascam is on. Doesn't change anything. I have even tried a different AC adapter for the Tascam. Just so strange it is only doing this with two guitars. I have also tested my guitar cords, and have tried different ones. They are all high quality cords as well.

 

[ecc83]

Actually I do have a meter, a $500 Fluke meter I used for work until I retired. I have rewired nearly all my guitars and have checked the circuits and all connections on these two guitars. They are fine. I have also checked the outlets for polarity and ground those are also fine. I have tried using a different circuit for the amp than the one the Tascam is on. Doesn't change anything. I have even tried a different AC adapter for the Tascam. Just so strange it is only doing this with two guitars. I have also tested my guitar cords, and have tried different ones. They are all high quality cords as well.

Ok! Would that be the Fluke 83? Got one, excellent meter.

My only suggestion now is that you do a comparative Signal to Noise Ratio test between a quiet guitar and a the hummy ones and post the results?

Dave.