RBI/RPM into power amp = ground loop?

Ray man · #1 08-07-2011, 04:03 PM

Im running the RBI into channel 1 and the RPM into channel 2 of the EV Q44 power amp. The Q44 only only has balanced xlr inputs, but im using the unbalanced 1/4' outputs coming from both sansamp's.
The cables im using have 1/4"(mono), to XLR jacks with jumper's across pin 1 and 3.

But there is a buzz!
Do I need to get rid of the jumpers on pin 1 and 3?

BassmanPaul · #2 08-07-2011, 04:13 PM

ART DTI isolator. Around $40 via Ebay. RBI unbalanced into DTI input 1. RPM unbalanced into DTI input 2. DTI output 1 balanced into power amp channel 1 and DTI output 2 balanced into power amp channel 2.

QED

billfitzmaurice · #3 08-07-2011, 04:18 PM

Quote:

Originally Posted by Ray man

Do I need to get rid of the jumpers on pin 1 and 3?

Sound System Interconnection

Ray man · #4 08-07-2011, 04:34 PM

Quote:

Originally Posted by billfitzmaurice

Sound System Interconnection

So it seems pin 1 should NOT be joined with pin 3.
The Q44 manual says its manditory to jump pin 1 and 3 or a six decible loss would result, thats why i joined them. But theres a hum.

Maybe I shoud mention im using the 1/4" uneffected out of the RBI into the RPM. Should i use the XLR uneffected out of the RBI instead? Im not sure if this applys.

Ray man · #5 08-07-2011, 05:35 PM

Anybody care to give me a yes or no? That would help.

Do i real need theART DTI isolator?

1958Bassman · #6 08-07-2011, 06:48 PM

Quote:

Originally Posted by Ray man

Im running the RBI into channel 1 and the RPM into channel 2 of the EV Q44 power amp. The Q44 only only has balanced xlr inputs, but im using the unbalanced 1/4' outputs coming from both sansamp's.
The cables im using have 1/4"(mono), to XLR jacks with jumper's across pin 1 and 3.

But there is a buzz!
Do I need to get rid of the jumpers on pin 1 and 3?

You have everything plugged into the same outlet/power strip, right? Do the 1/4" jacks have TR or TRS connections? You may need to make cables with TRS plugs, but wired for TR or TS to eliminate the buzz. Otherwise, try removing the jumpers- it may work.

Ray man · #7 08-07-2011, 10:52 PM

Quote:

Originally Posted by 1958Bassman

You have everything plugged into the same outlet/power strip, right? Do the 1/4" jacks have TR or TRS connections? You may need to make cables with TRS plugs, but wired for TR or TS to eliminate the buzz. Otherwise, try removing the jumpers- it may work.

yes, same outlet/powerstrip. Its just tip and sleeve.

Ray man · #8 08-08-2011, 03:08 AM

There is a ground lift switch on the back of the power amp. The problem is this; when grounded the RPM(ch 2) buzzes and RBI is silent. When ungrounded the RBI(ch 1) buzzes and RPM is silent.

Downunderwonder · #9 08-08-2011, 04:09 AM

Intuitively then, I'd make sure the RBI and the RPM share a common earth.

BassmanPaul · #10 08-08-2011, 12:13 PM

Quote:

Originally Posted by Ray man

There is a ground lift switch on the back of the power amp. The problem is this; when grounded the RPM(ch 2) buzzes and RBI is silent. When ungrounded the RBI(ch 1) buzzes and RPM is silent.

That's why the grounds NEED to be isolated per post #2.

Ray man · #11 08-08-2011, 12:58 PM

Quote:

Originally Posted by BassmanPaul

That's why the grounds NEED to be isolated per post #2.

Thanx Paul, i will take a look at the ART DTI isolator or something equal.

tech21nyc · #12 08-09-2011, 11:57 AM

Quote:

Originally Posted by Ray man

Im running the RBI into channel 1 and the RPM into channel 2 of the EV Q44 power amp. The Q44 only only has balanced xlr inputs, but im using the unbalanced 1/4' outputs coming from both sansamp's.
The cables im using have 1/4"(mono), to XLR jacks with jumper's across pin 1 and 3.

But there is a buzz!
Do I need to get rid of the jumpers on pin 1 and 3?

Are you trying to use both units independently or in parallel? There is a way to switch between the units by running one into the other but you need to follow the instructions in the manual. Are the units rack mounted? Try taking all the units out of the rack and see if the noise is still there. You may be best off using the XLR cables versus 1/4" to xlr. If you still get a ground noise there are instructions in our manual to cut one of the pins on the xlr cable.

Ray man · #13 08-09-2011, 12:54 PM

Quote:

Originally Posted by tech21nyc

Are you trying to use both units independently or in parallel? There is a way to switch between the units by running one into the other but you need to follow the instructions in the manual. Are the units rack mounted? Try taking all the units out of the rack and see if the noise is still there. You may be best off using the XLR cables versus 1/4" to xlr. If you still get a ground noise there are instructions in our manual to cut one of the pins on the xlr cable.

Lets see, I plug bass into RBI then into channel 1 of power amp. I take 1/4" uneffected out of the RBI into the RPM then from there into channel 2. So they are independant and there not rack mounted. It seems like the RPM is the one with the buzz. Even when my bass is not puged in and its worse with the mid boosted below 500hz.
I guess i will try removing the jumpers across pin 1 and 3 or try XLR to XLR.

Ray man · #14 08-10-2011, 01:48 PM

I was able to find the loop. It's between the uneffected out of the RBI and the input of the RPM, this makes the RPM buzz.
Conversly, if I take the uneffected out of the RPM into the input of the RBI, the RBI buzzes.

This is without my bass pluged in.
With my bass pluged in, both units buzz.

Ray man · #15 08-10-2011, 02:17 PM

The ART DTI isolator got some bad reviews. Would it even solve the problem?

Ray man · #16 08-10-2011, 05:55 PM

Will the Behringer MicroHD HD400 2-Channel Hum Destroyer do the job?

tech21nyc · #17 08-11-2011, 08:42 AM

Quote:

Originally Posted by Ray man

I was able to find the loop. It's between the uneffected out of the RBI and the input of the RPM, this makes the RPM buzz.
Conversly, if I take the uneffected out of the RPM into the input of the RBI, the RBI buzzes.

This is without my bass pluged in.
With my bass pluged in, both units buzz.

You didn't mention how your power amp is configured. Are you using two cabinets or is the amp bridged? Also, make sure that everything is plugged into the same AC circuit
.It would be best to go from the XLR outs of the RBI and RPM to the XLR ins of the power amp. Don't use the 1/4" to XLR cables.

Unplug everything but the RBI and power amp. Plug the RBI into one channel of your power amp and plug your bass into the RBI. If it's quiet go to the next step. Plug the RPM into the AC outlet and see if there is any additional noise. If not, plug the RPM into the other channel of the power amp and plug your bass into the RPM only. If it is still quiet, plug the uneffected out of the RPM to the input of the RBI. If that creates a ground loop it can be solved two ways. You can cut the shield on one end of the 1/4" cable that connects the RBI and RPM or you can insert something like the aforementioned products like the Ebtech Hum eliminator to solve the problem.

If you experience hum with either unit plugged into the power amp independently and without your bass plugged in, follow the instructions in the RBI/RPM manual to modify the XLR cable. You can also use the Ebtech Hum Eliminator as well. They make a version that works for both 1/4" and XLR.

BassmanPaul · #18 08-11-2011, 10:43 AM

Quote:

Originally Posted by Ray man

The ART DTI isolator got some bad reviews. Would it even solve the problem?

Don't believe every thing you read!

tech21nyc · #19 08-11-2011, 11:37 AM

Most of these types of hum eliminator boxes operate in the same manner. They use an isolation transformer. The impedance of the transformer is not always compatible with passive instruments. If the impedance is too low it will cause some tonal loss. This is easily remedied by inserting a buffered pedal between the hum eliminator and your bass or guitar.

Ray man · #20 08-11-2011, 12:05 PM

Quote:

Originally Posted by tech21nyc

You didn't mention how your power amp is configured. Are you using two cabinets or is the amp bridged? Also, make sure that everything is plugged into the same AC circuit
.It would be best to go from the XLR outs of the RBI and RPM to the XLR ins of the power amp. Don't use the 1/4" to XLR cables.

Unplug everything but the RBI and power amp. Plug the RBI into one channel of your power amp and plug your bass into the RBI. If it's quiet go to the next step. Plug the RPM into the AC outlet and see if there is any additional noise. If not, plug the RPM into the other channel of the power amp and plug your bass into the RPM only. If it is still quiet, plug the uneffected out of the RPM to the input of the RBI. If that creates a ground loop it can be solved two ways. You can cut the shield on one end of the 1/4" cable that connects the RBI and RPM or you can insert something like the aforementioned products like the Ebtech Hum eliminator to solve the problem.

If you experience hum with either unit plugged into the power amp independently and without your bass plugged in, follow the instructions in the RBI/RPM manual to modify the XLR cable. You can also use the Ebtech Hum Eliminator as well. They make a version that works for both 1/4" and XLR.

Thanx all, things are becoming more clear.
Im using 2 seperate cabs, and everything is pluged into the same powerstrip.
Everything is silent independantly until the 2 units are joined via the uneffected out. So its clear what the problem is.
Ok, so before I buy the ART or the Ebtech, I should try and snip the shield of the 1/4" to 1/4" ??? Were talking about a standard instrument cable from the uneffected out joining the 2 units right???