light buzzing in audio

[IA76]

Hi

 

A Behringer X1622 mixer is connected to an amplifier via a XLR (mixer end) to 6.25mm jack cable (amp end). There is nothing else connected to the mixer. There is a light buzzing noise coming from the speakers. Where is this coming from and what can be done to resolve this?

 

The amp does have mic inputs as well http://www.cie-group...a_480a_img5.jpg . WOul dI be better going XLR out from mixer to one of the mic inputs on the amp?

 

Thanks for your help.

[Shez]

How long is the cable? Balanced or unbalanced? Is the jack input balanced or unbalanced?

[Oldradiohand]

Is the buzzing on the output of the mixer? (use the headphone monitoring to find out) Does the amp buzz with nothing plugged in? Does plugging into the amp input cut the preamp output?

[IA76]

The cable is 1m. I'm not sure if it's balanced or unbalanced. It's just an XLR plug on one end and a 6.35mm mono jack on the other end.

 

If I disconnect the mixer from the amp the sound disappears.

[MarkPAman]

The cable is 1m. I'm not sure if it's balanced or unbalanced. It's just an XLR plug on one end and a 6.35mm mono jack on the other end.

 

Then it's unbalanced.

 

I can't find the spec of that particular amp, but it looks as if most of the InterM stuff uses balanced, so I'd try that first. You need a lead that is XLR to TRS jack (stereo Jack, except it isn't):

 

Pin 1 > Screen > Sleve

Pin 2 >>>>>>>>> Tip

Pin 3 >>>>>>>>> Ring

 

The Mic input may work with XLR > XLR cable if it can take a line level signal without distorting.

[sam.spoons]

If you have a TS (i.e. mono) jack on one end the cable must be un-balanced. This sounds like a 'pin 1' issue. It's quite common with differential balanced outputs feeding unbalanced inputs. You may be able to solve it by making a special cable with only the ground and hot wires (pins 1 and 2 in the XLR) connected, leaving the cold wire (pin 3) unconnected at the amp end.

 

Mark beat me to it http://www.blue-room.org.uk/public/style_emoticons/default/rolleyes.gif The user manual doesn't mention whether the amp in is balanced or not BTW. If using balanced doesn't help then see above.

[Sound Man]

Looking at the block diagram on page 17 of the manual the Amp In connection is unbalanced. Also it does imply that the mic inputs will handle line level inputs as long as they are kepted low level.

 

Interestingly looking at page 10 of the manual the 15 pin D connector is labelled as a Remote amplifier Input with a Balanced Input. Connection are via pins 1, 2 & 3.

 

Service Manual for the amp can be found here.

[paulears]

Just check that the buzz doesn't change as the lights are dimmed up and down = if it does, then it's coming from the dimmers, probably being carried by the mains cabling.

[mkfs9]

Get a balanced XLR lead. Sure to be OK then I think.

[paulears]

If you take the output from the mixer via pin 1 and pin 2, and leave nothing on pin 3 - you lose the audio - which is across 2 and 3 of course. Breaking the earth connection usually works, so wire a cable XLR pin 2 to the jack sleeve, and the tip connection to XLR pin 2 - leaving 1 unconnected. This breaks the connection to the mixer ground - The only snag will be if the ground path is still made via the earth cable connections. Audio earth is supposed to be separate to the case earth - the so called pin 1 problem. Lifting pin 1 at the XLR will be worth trying - it can only get better or worse!

[alistermorton]

so wire a cable XLR pin 2 to the jack sleeve, and the tip connection to XLR pin 2 - leaving 1 unconnected.

 

Tip to pin 3 surely?

 

 

 

[sam.spoons]

so wire a cable XLR pin 2 to the jack sleeve, and the tip connection to XLR pin 2 - leaving 1 unconnected.

 

Tip to pin 3 surely?

 

No, that's the 'cold' or -ve (except there isn't such a thing with ac.....) connection and in this case the one you can do without. In the case of much modern kit the outputs are "differential balanced" (i.e. no trannies or op amps) with the cold/pin 3 connection just being connected to earth via a resistor. There is a good reference article here http://www.rane.com/note110.html. My aux outputs are on TRS jack with tip = 2/hot, ring = 3/cold and sleeve = 1/ground in XLR terms. 9b is the one that worked in my case.

[alistermorton]

But Paul was describing connecting a T-S (no ring) jack and suggested connecting both to pin 2 (that's why I copied his original posting) which I'm sure was a slip of the finger.

 

So are you saying it should go sleeve to ground, pin 1, and tip to 2? Or sleeve to 3 and tip to 2? Paul is suggesting leaving pin 1 unconnected.

 

I'm not really that well up on the sound side, so I'd like to avoid getting it barse ackwards if I ever have to do something similar.

[sleah]

I've always gone from XLR to TR Jack as follows (in either direction)....

 

XLR Pin 1 (Earth or Screen) to RING on the jack.

XLR Pin 2 (Line or Hot) to TIP on the jack.

XLR Pin 3 (Return or Cold) left unconnected OR shorted to Pin 3.

 

Wouldn't connecting jack RING to XLR Pin 3 and leaving XLR Pin 1 unconnected cause some potential sillyness when it comes to earthing and hum (ground loop?)???

 

This is assuming no external transformers or earth lift devices are in the pathway.

[dbuckley]

Other than a two pole jack is a TS rather than TR, yes, that's the way.