Help diagnose my buzzing please

gotfunk21 · #1 07-23-2011, 05:53 PM

I just got a used 700rb-ii from ebay, and a brand new neo 112-ii. I'm really excited, I plug in, and it's crazy noisy.

I checked all the speakon pins to ensure they're fastened securely. I'm using the same bass and instrument cable I use each week for church. I played through a 1001rb for over 2 years at church. I've never heard an amp this noisy.

To ensure it's not my room, I ran the bass through the amp DI, and my sansamp DI. The sansamp is quiet. The GK DI has similar buzzing. Sweeping the volume causes some significant crackling too.

Here's a youtube clip of the sound from the speakers, and an audio clip of the amp's DI straight into a recorder, without any instrument at all plugged in. All settings are at 12'oclock, and I'm just sweeping the volume from 0 to 12'oclock. I do have the ground switch on. I A/B'd the DI with and without the ground and heard no change. Left it on to be safe.

I'm going to take the head in on Monday ... but I'd love to hear any suggestions/thoughts.

‪GK 700rb buzzing‬&rlm; - YouTube
http://jacobsowinski.com/audio-sampl...-vol-sweep.mp3

craig.p · #2 07-24-2011, 05:44 AM

Could be internal shipping damage, like a broken solder joint, or a cracked circuit board trace, or a connector or ground screw that came loose. That's assuming the unit was good when it left the seller.

Dekker · #3 07-24-2011, 06:37 AM

It does indeed sound like a 60Hz/ground hum. From the video, it appears like there is no obvious electrical equipment nearby (interference)... Have you considered trying a different power cord? If it is a standard IEC cable, you can use the power cable from your PC to test.

I don't know about your comfort level or skill with electronics, but if you don't plan on returning it or using any 'warranty' you might have, consider popping off the top and looking for 'obvious' faults. Of course, if you are not knowledgeable about electronics, I don't suggest that since it can get dangerous!

Also, according to the manual, you're not supposed to connect the 380 and 50w to the same speaker... I don't know the particulars of how you're wiring the back of your amp to the speakers, but might want to review that as well, since I think pins +/-1 are 380 and +/-2 are 50. If your cable or speaker combine the two, you might be doing bad mojo to your amp.

Hope you find out what the problem is though, since it is frustrating having a new purchase that does not work!

gotfunk21 · #4 07-24-2011, 01:55 PM

Thanks.
I am using the 4 pin speakon cable that came with the cabinet from GK for biamping. Regardless, I actually have the cab set on "full range" (although, there's still the buzzing whether it's in biamp or full range)

I'll try a different power cable and take it to another room with fewer electronics and lights.

**B-string** · #5 07-24-2011, 02:24 PM

That input gain control really needs cleaning! Could be the whole problem or could have been hit in transit. Could also be a problem with the input jack, the gain control is after the first stage. Try the DI pre and post, as well as the Tuner out to help isolate the stage.

lbwdog · #6 07-24-2011, 02:56 PM

That's pretty bad my friend.

Have you tried.........
A different bass?
Another room on a different electrical circuit?

Sounds to me like you might be close to a rheostat, or some neon lights.

1958Bassman · #7 07-24-2011, 03:14 PM

Quote:

Originally Posted by gotfunk21

I just got a used 700rb-ii from ebay, and a brand new neo 112-ii. I'm really excited, I plug in, and it's crazy noisy.

I checked all the speakon pins to ensure they're fastened securely. I'm using the same bass and instrument cable I use each week for church. I played through a 1001rb for over 2 years at church. I've never heard an amp this noisy.

To ensure it's not my room, I ran the bass through the amp DI, and my sansamp DI. The sansamp is quiet. The GK DI has similar buzzing. Sweeping the volume causes some significant crackling too.

Here's a youtube clip of the sound from the speakers, and an audio clip of the amp's DI straight into a recorder, without any instrument at all plugged in. All settings are at 12'oclock, and I'm just sweeping the volume from 0 to 12'oclock. I do have the ground switch on. I A/B'd the DI with and without the ground and heard no change. Left it on to be safe.

I'm going to take the head in on Monday ... but I'd love to hear any suggestions/thoughts.

‪GK 700rb buzzing‬&rlm; - YouTube
http://jacobsowinski.com/audio-sampl...-vol-sweep.mp3

That's not power supply ground noise- 60Hz is close to the B on your A string and that's definitely not low enough to be a ground loop. It could be a cracked circuit board ot potentiometer if the input knob was bumped, though.

Did the noise go away when you touched the strings or anything connected to the strings/bridge? That alone tells me that it's a problem in the input stage, not the power supply ground. The crackling could be as simple as a dirty control.

FYI- if you grab a mic while your other hand is on the strings or bridge, get ready- that can be a major problem if the damage is causing you to complete the ground circuit. Take it in and have it serviced ASAP.

BTW- if you meant 'speaker plug pins' when you posted about the Speakon pins, the only things that plug could cause is a dead short (hard to do if the Speakon isn't badly damaged) or an open circuit (if one or both pins are missing).