Preamp Buzz/Hum - Is this an impedance issue?

[huntgl]

Hello all :-)

I have been recording some bass by DI into my preamp/channel strip. The bass is equipped with a humbucker and it is being plugged directly into the unbalanced 'Instrument' input on my preamp, but it seems to generating quite a bit of buzz/hum. I recorded the following link by connecting the balanced output from the preamp into a small Tascam DP-004:

soundcloud.com/victorludorum/preampbuzzhum

I raise the gain on the unit, firstly to 9 o'clock, then to 12, and then to 3. The maximum gain on the unit is 70db I believe. When I touch the strings on the guitar the buzz doesn't go away which leads me to believe that there is no grounding issue with the bass wiring.

Does this sound to you like a faulty channel, or is it just an impedance issue where I might need to use a separate DI type box?

Any thoughts would be greatly appreciated ;-)

Cheers all!
Gary.

[JohnH]

I havnt heard that sound before, it seems not like a normal mains buzz. have you tried going through some kind of buffer before the input (eg a stomp box or processor)?
J

[huntgl]

I'm going to test that theory this week if I can find a suitable DI that I can borrow/test. If that removes the buzzing without affecting the sound, then I guess it's an impedance thing...

[sumgai]

Dec 14, 2012 4:44:32 GMT -5 huntgl said:

When I touch the strings on the guitar the buzz doesn't go away which leads me to believe that there is no grounding issue with the bass wiring.

This would not be the normally expected result when touching/untouching the strings. Unless you live where there's no magnetism or electricity, then there's going to be some (hopefully very small) amount of hum. Since it's ElectroMagnetic in nature, it seeks large objects to act as antennae, and your body qualifies for such distinction. When you touch the strings, you are grounding your body, not the other way 'round. That means that whatever your body was receiving/conducting into the pickups is now supposed to be going into the ground portion of the circuit, and thus it should become inaudible to the pickups/the rest of the amplifier system.

If that's not happening, if the hum stays the same level, then either the instrument is not correctly connected to the amp/stompbox/etc., or else the hum is being introduced by some other device that comes after the guitar/bass itself. By that I mean starting with the cable out of the jack, and heading towards the amp, something is acting as a receiver/conductor. FWIW, poorly built cables have been known to do this.

HTH




sumgai

[huntgl]

I'm pretty sure that the unit is fine. I have tried it with an acoustic guitar that has an undersaddle piezo type pickup, and it was totally silent. I also tried it with a freind's factory wired Gibson (with 2 humbuckers) and his guitar was noisier than mine. Maybe that says a lot about 1990s Gibson factory wiring, but it makes me feel confident that mine is ok. I'm hoping to try the stompbox thing this week if I can find a way of getting hold of one....

Thanks for the replies so far, it's appreciated as always ;-)