GK MB200 - confusing situation

Slowgypsy · #1 08-03-2011, 08:29 PM

I've gigged GK equipment for years... definitely one of the happy customers... and this is NOT a bash GK post. So on to my confusing situation...

One group I play with has a steady-every-other-week gig in an old bar/pub in NYC. Typically I bring my GK RB700-II and run it into 2 GK Neo 112 cabs. Way more firepower than what's required but the sound works for me. And there have been absolutely no issues whatsoever.

In an effort to travel lighter, last time I used my GK MB200 and ran it into 1 Neo GK 212 cab. Did my sound check, used my Line 6 G30 wireless... everything is perfect... more than enough headroom, etc for this venue.

At the last minute, for reasons I'm not entirely sure, I decided to skip the wireless thing and just use a cable to plug directly into the amp. Dang... loud hum/hiss/noise. Not good. I set my bass with 2 single coil pups into even blend mode... sort of makes 1 big humbucker... did not solve the problem. If I kept my hands on the strings the noise went away. The instant one of my hands was not touching the strings the noise instantly appears. This was not a subtle noise either. I made it though the first song... but not good.

I quickly lost the cable and went back to the G30 wireless rig. The noise issue disappeared completely... and the rest of gig continued without issue.

The next day, in my studio, I used the same equipment/bass/cable/etc and tried to re-create the situation. I could not do it. Everything sounded just fine. No noise.

So... anyone have an insight into what was going on to create that noise?

AdamJames306 · #2 08-03-2011, 08:34 PM

Sounds like a grounding issue to me. I don't totally understand the topic, I'm sure someone on here does, but it's definitely not a problem with your amp. More likely a problem with the venue. I'm in NYC too. Where were you playing?

PurpleDrank · #3 08-03-2011, 08:37 PM

Yup, sounds like a bad outlet (ungrounded, on a circuit with lights, etc.) in the venue.

Slowgypsy · #4 08-03-2011, 08:40 PM

Quote:

Originally Posted by AdamJames306

Sounds like a grounding issue to me. I don't totally understand the topic, I'm sure someone on here does, but it's definitely not a problem with your amp. More likely a problem with the venue. I'm in NYC too. Where were you playing?

Venue is 11th Street Bar in the east village. No doubt the wiring is funky. But I've used my RB700 head there many times before, using a cable, running electric stuff exactly the same without any issues. And somehow with the MB200, using a cable was n/g but using wireless was okay.

Bass Mule · #5 08-03-2011, 08:58 PM

You got a ground lift switch on your D.I.? Or the club's D.I.? If you're using the D.I. on your heads (either), one might have the switch in the "lifted" position, and the other is not.

(I can't remember if they have ground-lift switches on those heads on the D.I.)

Every once in a while I run into this too. It's not the equipment at all, but a grounding issue in the venue (like the above posters mention). Invest in your own D.I. with a ground-lift switch. I use a Tone Bone Bassbone.

Bass Mule · #6 08-03-2011, 09:04 PM

Just checked the pdf manuals available on the GK website. Both heads indeed have a built-in D.I., but the 700rbii has a ground lift switch, while the mb200 does not. If you were using the D.I. at this club (to go to the front of the house), I can pretty much guarantee this was your problem. The switch on your 700rbii is probably in the "lift" position, explaining why you don't get that hum when you use that equipment at that venue.

lookiel · #7 08-03-2011, 09:54 PM

Nailed it!

Anarchyok · #8 08-03-2011, 10:47 PM

Not sure thats the solution, as the MB200 is always ground lifted - ie, you cannot engage the ground from the DI included.

Slowgypsy · #9 08-04-2011, 03:59 AM

Quote:

Originally Posted by Bass Mule

Just checked the pdf manuals available on the GK website. Both heads indeed have a built-in D.I., but the 700rbii has a ground lift switch, while the mb200 does not. If you were using the D.I. at this club (to go to the front of the house), I can pretty much guarantee this was your problem. The switch on your 700rbii is probably in the "lift" position, explaining why you don't get that hum when you use that equipment at that venue.

No cigar. I was not using the DI. This is a small venue, only running through my cab. There is no ground lift switch on the MB200.

So why would I get the bad noise using a cable, but when I switched to wireless the noise completely went away?

WingKL · #10 08-04-2011, 05:02 AM

Perhaps the shielding on your cable has gone bad or is insufficient. Have you tried another cable?

Mark Reccord · #11 08-04-2011, 07:17 AM

Sounds like a cable issue to me. If it was a grounding/amp-related problem you'd expect to have it with the wireless system as well.

billfitzmaurice · #12 08-04-2011, 08:14 AM

Quote:

Originally Posted by Slowgypsy

So why would I get the bad noise using a cable, but when I switched to wireless the noise completely went away?

Because of the short length of wire between the bass and the radio transmitter. With high impedance pickups the cable acts as an RFI antenna, and the longer the wire the more RFI it picks up. Each doubling of the wire length squares the noise pickup. The worst case is if you inadvertently were to use a speaker cable rather than an instrument cable, as the lack of shielding would compound the noise by an order of magnitude.

scottfeldstein · #13 08-04-2011, 08:22 AM

Bad power in the venue. Becomes an issue when you're corded to the amp, not when you're wireless. Obviously when you're corded you're completing a circuit to the ground with your feet. Not when you're not.

I just made that up.

bound'n'blocked · #14 08-04-2011, 09:05 AM

I had something similar happen to me at a show once right after I got my MB200. I went from the bass to my Sansamp BDDI to the head, and used the XLR out on the Sansamp to the board. Loud noise. Switched DI's to a standard Radial DI, same noise. I finally took the pedals/DI out of the chain and just went with the head/cab and used the DI on the amp and the sound went away. I haven't had an issue since and I've used the Sansamp every time I've hooked it up. I'd say it's a power issue at the location.

BnB

Slowgypsy · #15 08-04-2011, 11:34 AM

No doubt it's some kind of bad power at the venue. And these old NYC bar/pubs are funky in every sense of the word.

The cable I used is the cable I always use. It's not bad. As I mentioned I could not repeat the situation when I was back in my studio. And I used the exact same amp/cab/bass/cable/etc that I used at the gig.

I set up the electrical power distribution at the venue with extension cords and socket strips. And I did it exactly the same as I've done dozens of times before.

The only different thing was using my MB200 instead of my RB700-II.

Now... the lead guitar was using different pedals, and also used a tube mic preamp... which he's never done before. Could those items in the electrical chain have caused my situation?

Hoping to have some "food for thought" before we return there next week.

Slowgypsy · #16 08-04-2011, 11:37 AM

Quote:

Originally Posted by billfitzmaurice

Because of the short length of wire between the bass and the radio transmitter. With high impedance pickups the cable acts as an RFI antenna, and the longer the wire the more RFI it picks up. Each doubling of the wire length squares the noise pickup. The worst case is if you inadvertently were to use a speaker cable rather than an instrument cable, as the lack of shielding would compound the noise by an order of magnitude.

I like this line of thinking, but I'm curious why I never experienced it with the RB700-II and only the MB200. Was using same cable, same bass.

AwkwardLoudness · #17 08-04-2011, 12:23 PM

Were there any neon signs nearby at the gig? Those can also induce unwanted noise. Poor grounding of the outlet seems most likely, however.

5port · #18 08-04-2011, 04:51 PM

I always carry one of these to gigs:

It will tell you if the wiring is correct or not. If not you can take steps before the first set to save getting shocked from a mike, etc. In the case of the MB200 (a switching amp) it will be less tolerant to say swapped wiring than an analog amp. I'm afraid in this situation best bet is to stick with the analog amp. Using the wireless is another work around of course.