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buzz/hum sound from bass amp DI output Need some Guidance


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hello folks, I am in serious need of help.  With some changes in the worship band at the church I run sound for, we have a different bass player than before.  I had mic'd the previous bassist amp, as that was what the worship leader at the time wanted and had no issues with buzz or hum.  Now when they left, they took all of their equipment with them, so I had to scramble to get the new bassist into the system, and he has a DI out on his bass amp head.  I just plug in an xlr from that to the snake to the board.  I cannot for the life of me get rid of the buzz/hum at all.  Plugged his amp into a different circuit breaker, changed power cord, tried ground lifting his amps power cord, using the ground lift on the amp itself, changed xlr cable, tried a different channel on the snake, and mixer, and nothing makes it better.  Now I will say that the sound from the speaker has just a TINY hint of a buzz/hum, but when it is ran thru the mixer it is WAAAY loud.  I have run his channel thru a compressor with a gate and turned the gate up to try to hide the buzz/hum, but therein lies another issue.   depending on the song being played, he plays softly, and I have to lower the gate to let that thru, but then the buzz/hum is there and its quite loud during a quiet song.  What else can I try???  I would like to go back to mic his cabinet, but don't have any microphones to do that with, and no cash to buy one either.  Would a DI box work?  Do they even make a DI box with xlr input and output?  And how much would that run me?  Thanks for the help!

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Some amps have noisy outputs, especially older ones, which is why it's standard industry practice to use a DI box on bass. You'd plug the bass guitar directly into the DI, then the 1/4" loop out (using another guitar cable) to the input of the amp. The XLR output of the DI box would go to your mixer, and you wouldn't use the XLR output of the amp at all. And before you say "but then you wouldn't get the tone of the amp", that's often another part of the reason to do it that way. In the professional world, it's rare to use the direct out of an amp, although it happens occasionally. Amps are generally better quality these days, so it's a little more common than it used to be.

If the amp itself is noisy, and you can hear it in the speaker, putting a DI before the amp should solve the problem. 

It's also possible that it's the guitar and not the amp, then you've got a slightly bigger problem on your hands.

DI's don't usually have XLR inputs, since they're made to take an unbalanced instrument level input and turn it into balanced mic level. The closest thing would be an iso transformer, and there are a lot of options out there for those. The Radial ProAV1 DI can take a balanced XLR line level signal and turn it into a balanced mic level signal. Actually, the ProAV1 is a great all-purpose DI, it can take mono or stereo inputs from pretty much any device and turn them to mono mic level. One of my most used DI's, since it can do just about anything.

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Posted (edited)

Is the Built in DI out on his Bass amp balanced? I ran into one before that had an XLR out but only Pin 1 and 2 had a signal. I can't remember the bass amp off the top of my head.  If the problem is just too much try a DI "Between" the Bass Guitar and Bass amp as B. Adams mentioned above. I know it's not the best solution impedance wise but if all else fails it may work for a temporary fix. Just go out the guitar with a 1/4 inch cable, into the DI and out with a 1/4 inch cable to the Bass amp. Use the XLR out to go down to the Desk. If you don't have a DI box to spare hit up your local Pawn Shops for a used microphone/DI box. Sounds like even a used SM58 or whatever would be better than the setup your using now. Honestly if the church can't come up with a few dollars for a microphone or DI box it sounds like they don't value your services much.

Doug

Edited by Dookietwo
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I will look into his amp some more, but I cannot say if it is a balanced DI out on his amp head or not.  I don't hear the buzz/hum when standing by his gear or whether hes playing or not.  I will def look more into his amp and find out if it actually is balanced xlr outs on it.  Even so, i may still get an iso box.  I thank you both for your thoughts and suggestions, and will try to post an update tomorrow afternoon, and go from there.

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Must be an Ampeg :).

Famous for having poor line outs (not bagging on the tone :). As stated above, many (mostly older) amps have internal DI issues. Also as stated, try a DI in line between the instrument and the amp. Amplified acoustic instruments are very prone to noise inductance.

A question would be "Is the signal to noise ratio acceptable (rarely noticed by your audience) listening to the speaker only"? If you say yes then the instrument isn't the majority of the problem and a DI before the amp should do the trick. If you do this, one thing you should be aware of is you now control of their tone (sans the instrument and their technique) so you might need to EQ/comp that channel to make it sound it's best. Also if the instrument has hum passive pickups, be ready for a pretty low input signal (how quiet is your board?). I usually prefer this arrangement (it is often cleaner and the control allows for a better mix).

DI's are also cheaper (usually) and less fragile than a good mic. There is also no bleed into that channel from other things on the stage (rarely an issue with close mic'd amps but still.....).

Hope this helps

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sorry i hadn't gotten more information on this since my previous reply.  It is a carvin amp, the speaker he runs off the amp itself has just a slight buzz/hum, but the DI out is quite loud in the mains.

This past Sunday I went back to the previous channel and mic cable as changing channels the week before did not get rid of the sound.  I did have just a slight buzz/hum from the bass, but it was pretty quiet.  even turning off the gate it was there but not very noticable even if it was quiet between songs.  I don't know what would have changed.  His gear was plugged in to the same outlet thru the same extension cord for his gear. 

I am considering an ISO block to try in between the amp di output and the board to get rid of the buzz/hum.  But with the lack of issues this past weekend I am unsure what to do.  I am going to see what happens this coming sunday and see what happens then.

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4 hours ago, ChadGrieser1979 said:

sorry i hadn't gotten more information on this since my previous reply.  It is a carvin amp, the speaker he runs off the amp itself has just a slight buzz/hum, but the DI out is quite loud in the mains.

This past Sunday I went back to the previous channel and mic cable as changing channels the week before did not get rid of the sound.  I did have just a slight buzz/hum from the bass, but it was pretty quiet.  even turning off the gate it was there but not very noticable even if it was quiet between songs.  I don't know what would have changed.  His gear was plugged in to the same outlet thru the same extension cord for his gear. 

I am considering an ISO block to try in between the amp di output and the board to get rid of the buzz/hum.  But with the lack of issues this past weekend I am unsure what to do.  I am going to see what happens this coming sunday and see what happens then.

With no one around have the bass amp on. Have the Microphone cable plugged in and have the system up just enough so you can hear the hum/buzz in the pa. Move the microphone cable all around that is plugged into the bass amp. Does the hum/buzz get louder and softer as you move the microphone cable around? I'm wondering if there is some reason something is going microphonic.  Set the cable on top of the bass amp, around power supplies/wall warts, move that mic cable all around. A microphone cable "should" kill noise like you describe but there may be something else wrong that is making the noise. 

Edited by Dookietwo
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Thanks for that suggestion, I will check it out Wed before practice and will report back what I find out.  We did have some sound out of his amp again this week, probably about halfway between what was first noticed and last week where there was very very little.

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