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RBI 60cycle hum

cb56

cb56

Jul 2, 2000
4,342
354
Ozarks
#1
Update! scroll down to post #18 to see the unhappy ending.
Any of you RBI users have a problem with a 60 cycle hum. If so where you able to correct it?
I got mine new from music123. I noticed the hum when I first set it up with my power amp. I've eliminated everything before the pre amp (it hums even with nothing plugged into the input) It's not real loud and does not get louder when I turn the pre amp up. If I shut the RBI off and leave the power amp on, hum goes away. I use a short sheilded cable going out from the RBI to my power amp input. I have tried 4 different cables with no improvement. I can improve it quite a bit by using a ground adapter on the RBI only and leaving everything else grounded normally. Although I suspect this is not recommended.
I didn't think this was going to be a problem because the hum is very faint going through my bass rig so I went ahead and sent in the warranty card and wrote some of my favorite setting in the manual. My soundman says he can't use the XLR out to go to the board because it picks up the ground hum. If I try to return this to music 123 they will charge me a 15% restocking charge because I wrote in the manual, plus I pay for shipping.
In short I think I screwed myself. Too bad because I really love the tone I get out of the RBI.
Helpful suggestions are appreciated
 
#5
need one of these from the electronics parts store....maybe

pRS1C-2266744t98.jpg

3prong ground plug adapter.

put it ONLY on your rbi.

Don't give up so soon, RBI has lots of flexibility to it. another possibility is noise in the powerline, boosted by RBI, boosted by amp again. like a refridgerator on the circuit!
 
#8
billfitzmaurice said:
You've got a ground loop, in both situations. Here's where you learn how to fix it:
[Invalid or Expired Link Removed]
Click to expand...
Hate to sound ignorant but most of that is greek to me. I am using a 1/4 to 1/4 cable with just one wire and the sheilding. Same as I used with my Ampeg pre amp that I didn't get any hum with. Should I be using what they are calling a balanced cable with 2 wires and sheilding for this? Also i'm not giving up on the RBI, I love the tone I get with it. I just don't understand why with my old preamp I got no hum and with the new one I do. Nothing else has changed. I did try the 3prong adapter on the RBI only and it did help until the soundman plugged in his cable. Then hummm city. But if that is potentially dangerous I don't want to continue using it.
 
#9
cb56 said:
I am using a 1/4 to 1/4 cable with just one wire and the sheilding. Same as I used with my Ampeg pre amp that I didn't get any hum with. Should I be using what they are calling a balanced cable with 2 wires and sheilding for this? .
Click to expand...
You should if the pre has an XLR out and the amp has an XLR in. Otherwise make up a 1/4 to 1/4 with the conductor attached at both ends but the shield attached at one end only.
I did try the 3prong adapter on the RBI only and it did help until the soundman plugged in his cable. Then hummm city
Click to expand...
Same deal, try an XLR cable with the shield connected at one end only. Otherwise a transformer DI with a ground lift is necessary. I'd also complain to RBI, this should not happen and is an indication of a design defect, especially if it happens with a balanced connection.
 
#10
Bill, first of all, thanks for taking the time to help me out with this. I really appreciate it.
So you're saying that if I take a 1/4 inch shielded cable and disconnect the shielded mesh from one of the 1/4 plugs that will help? I'll check it out.
Also maybe I will get in touch with Tech 21 and see what they can do for me. After all it is new and does have a warranty.
Thanks again.
 
#11
also btw, the RBI does have XLR outputs and my power amp has XLR inputs. I did try using those and it didn't seem to help. Of course I was using a 20 ft. mic cable which is all I have at the time with XLR plugs so it might not have been the best way to do this.
 
#12
cb56 said:
also btw, the RBI does have XLR outputs and my power amp has XLR inputs. I did try using those and it didn't seem to help. Of course I was using a 20 ft. mic cable which is all I have at the time with XLR plugs so it might not have been the best way to do this.
Click to expand...
A 20 ft cord isn't going to add noise if everything is as it should be, so IMHO the pre may be AFU. While unbalanced 1/4 to 1/4 interconnects are an invitation for ground loops, balanced XLRs by design should eliminate any possibility of a ground loop, even when using a 150 foot snake. The unit may be defective, either due to a manufacturing glitch or by design. With an outfit like Tech 21 you'd certainly expect it to be the former and not the latter. On the off chance that your power amp is at fault I'd try the pre with a different one to be sure.
 
#13
Ok. Just set everything up and here are the results.
Disconnected the sheild (mesh) on one end of the 1/4 to 1/4 plug. This actually made the hum louder by about 10 times.
Tried my mic cable with XLR's again this time laying the excess cable on top of my amp rack avoiding having it cross with any power cables etc... Humm was very quiet but still there. Tried the RBI pre amp with my battery operated headphone amp using the mic cable again and it hummed through that also. So I think I have a defective pre amp and should try to get it repaired or exchanged.
 
#14
Bill's right,after trying all those shielding/balanced unbalanced things your RBI needs to be looked at by Sansamp.I use a Y connector with a couple of simple shielded cables to each side of my poweramp and have never had that kind of noise.I've been tied into some large outdoor PA systems at summer festvals with mine and the soundmen have always been happy,even without a ground lift switch on the RBI and lots of lights.Sorry man,you better have someone look at it.
 
#15
Blues Bass 2 said:
Bill's right,after trying all those shielding/balanced unbalanced things your RBI needs to be looked at by Sansamp
Click to expand...
For sure, if breaking the shield connection makes things worse then it would seem that an internal ground connection is missing. That's potentially quite dangerous, as AC current could conceivably flow through your interconnects.
 
#16
OK, thanks again for all your help. I sent an email to Tech21 describing the problem (including a link to this thread) and will call them over my lunch hour tomorrow. If nothing else I'll get to report in to everybody here about their customer service.
In the mean time I'll need to figure out what I'm going to play through on my gigs when I have to ship this in to the factory. I might just get the pedal version of the sansamp to use in front of my power amp. That way I'll also have it for emergencies etc...
 
#18
So here's the update.
Lloyd at Tech 21 told me to send the RBI unit in. I sent the RBI in two weeks ago on tuesday.

Since I needed something to play through the next weekend I bought a Sansamp BDDI, the small battery operated pedal version. I used it with the exact same setup. Same basses, power amp, cables, speakers etc.... I had no hum at all anytime using the BDDI with my rig.

Tech 21 received my RBI the following friday. They sent it back the following tuesday saying they couldn't find anything wrong with it at all. When I received it friday I plugged it into my headphone amp and heard the same hum. Same thing with my power amp/speaker set up that had worked perfectly with the BDDI and my previously owned Ampeg pre amp. Today I took it and my headphone amp to where I work just to make sure there wasn't something wrong with the power at my house even though it has hummed at every gig I've used it at. Same hum at work in our 3 year old building. I also took it into where my wife works just for yet another test. Same hum!
So today I called Tech 21 again and was told that they had 2 techs check it out and they could not get it to hum! Imagine that! They can't get it to hum and I can't get it not to hum! Anyway they said that they could not do anything else for me and that I should just send it back to where I got it for a refund. So I guess I'll be pre amp shopping again soon.

So anyway folks, that's my experience with Tech 21 and their products, customer service etc....
 

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