Excessive noise from XLR output + Rig concerns

mkentbass · #1 05-15-2011, 06:57 PM

Hi all,

I am getting excessive noise from the XLR and 1/4" outputs on my DBX 231 graphic EQ. I patch my active bass directly into the 231 using the 1/4" input. From either the XLR or 1/4" output, I receive excessive noise. In the future, I want to be able to run the 231's XLR output into the input of a power amp without any noise or impedance issues. What are my options?

Thanks for the help!

Zooberwerx · #2 05-15-2011, 07:12 PM

The dbx 231 is really designed to be used as a line-level component (FX loops, mixer inserts, etc.). I can not speak with any certainty as to how it would respond to an instrument input. For that fact, I've never heard of anyone attempting this application before. Are you using a preamp of any type?

ftp://ftp.dbxpro.com/pub/PDFs/Manual...esManualA2.pdf

Riis

mkentbass · #3 05-15-2011, 07:35 PM

As of now, I am not using a preamp. I have been using the 231 at instrument level input with success. As a matter of fact, I can use either output on the 231 (XLR or 1/4") to drive the input on a small combo amp.

Zooberwerx · #4 05-15-2011, 07:44 PM

Quote:

Originally Posted by mkentbass

As of now, I am not using a preamp. I have been using the 231 at instrument level input with success. As a matter of fact, I can use either output on the 231 (XLR or 1/4") to drive the input on a small combo amp.

So you were using the 231 with success (no noise) and now you're getting excessive noise? What has changed in terms of your signal chain? Is the noise now present when running the same small combo amp?

Riis

mkentbass · #5 05-15-2011, 07:56 PM

In terms of success, I believe I do not have any impedance issues from the 231's output. However, I still get a lot of excessive noise when running either the XLR or 1/4" output. Previously, I tested for possible noise sources. First, I used an XLR to 1/4" cable from the 231 to the combo amp (my bass was not connected to the 231's input at the time). I received excessive noise. Next, I added my bass to the 231's input using instrument cable, and the noise was still present through the combo amp. I tried swapping cables, (from the XLR to 1/4" to an instrument cable), between the 231 and the combo amp. I still receive excessive noise. So no matter what I do, the noise is still present.

uhdinator · #6 05-15-2011, 11:36 PM

You're doing it backwards. Bass to amp,
Pre amp out/ send into 231 with inst cable, 231 out with inst cable into return.

The EQ is designed to run at line level. Your instrument level is a lot closer to the noise floor than line level would be so when you amplify what's coming out of if your boosting the noise too.

I would not call that successful results.

T-Bird · #7 05-16-2011, 12:00 AM

Hi.

Page ten, paragraph #2 on the manual Zooberwerx posted.

Using any balanced signal system with unbalanced sources is also not very bright thing to do. It can be done, but takes a lot of know-how.

Regards
Sam

Zooberwerx · #8 05-16-2011, 04:46 AM

Quote:

Originally Posted by uhdinator

You're doing it backwards. Bass to amp,
Pre amp out/ send into 231 with inst cable, 231 out with inst cable into return.

The EQ is designed to run at line level. Your instrument level is a lot closer to the noise floor than line level would be so when you amplify what's coming out of if your boosting the noise too.

I would not call that successful results.

I'm a little confused with the OP's plight as it now appears the noise was ever-present although the resulting signal had enough oomph to feed a small combo amp. uhdinator's suggestion makes perfect sense.

*The 231 would be best suited placed in the FX loop of a conventional preamp or placed between a simple tube (mic type) pre and the power amp.

*The 231 is not appropriate for use a dedicated preamp. On the bright side, a modest tube pre (no built-in EQ, etc.) can be had for low dough. Run your bass into that, then feed the resulting line level signal to the 231 and power amps downstream.

You're oh-so close!

Riis

mkentbass · #9 05-16-2011, 07:21 PM

Thanks for the help! Even if I lowered my instrument-level through the pre-amp to line level, would I still be able to drive a power amp with one of the outputs on the 231?

Zooberwerx · #10 05-16-2011, 08:41 PM

Quote:

Originally Posted by mkentbass

Thanks for the help! Even if I lowered my instrument-level through the pre-amp to line level, would I still be able to drive a power amp with one of the outputs on the 231?

That's right, "even if..." It's a waste of your time and resources. Get a decent preamp, sell the dbx 231 as you really don't need umpteen GEQ bands, and be done with it.

Riis

uhdinator · #11 05-17-2011, 11:43 AM

It sounds like you are not understanding things. Line level is not lower than instrument level.

Instrument level must be amplified to line level by a pre amp. Then line level to a power amp connected to a speaker. Using an EQ should be done from a send on the combo amp (line level from preamp) to EQ then back out to Return (line lev input)
to the power amp of the combo amp.

Combo amps have a preamplifier and power amp. If you were plugging the EQ into the front of the combo amp which guessing here. Then this is what you have:
Inst level to EQ plus added noise into a Preamp then power amp. = amplified noise.

IF THE AMP HAS NO SEND/RETURN,
GET RID OF THE EQ AND JUST USE THE COMBO AMP! you don't need another pre amp to feed the EQ cause then you are sending the line level of the EQ into a pre amp on the combo. NOT good.

I'm guessing the combo amp is not a bass amp and you're trying to make it sound like it by using an EQ.