light buzzing in audio

[sam.spoons]

This article http://www.rane.com/note110.html will tell you all you need to know about the various ways you can connect different bits of audio equipment together.

 

There's also a very good explanation of how balanced audio works here http://mikeriversaudio.files.wordpress.com/2010/12/balanced-unbalanced_revised.pdf (which also corrects my dodgy terminology earlier)

 

In a transformer balanced output both hot and cold are isolated from the ground/screen because this gives maximum rejection of interference (the signal is equal and out of phase in the two conductors). For this you would need to make a cable with the pin 3 connected to pin 1 at the mixer end but unconnected in the TS jack at the power amp end (cable 5 in the Rane reference guide).

 

In many modern pieces of kit the cold is connected to (or if you like isolated from) ground via a resistor equal to the impedance of the output, this works well if the input it is feeding is also balanced but can be troublesome when feeding unbalanced inputs (the 'pin 1' problem). There was a long thread on the old Mackie DL1608 forum as said mixer exhibited just this problem (and does indeed have it's outputs 'balanced' in this way). The aux outputs in this case are on TRS jacks and solution was to make a special TRS-TS lead which left the ring unconnected at the mixer end (cable 9) effectively the same as leaving pin 3 unconnected on an XLR-TS jack lead. There is a 6dB loss with this as you are losing the out of phase part of the signal

 

HTH

[paulears]

When hum is a problem then balanced outputs can provide isolation so yes don't use pin 1 on the output device at all. Balanced outputs don't need an earth to work. It's still a bit of a gamble, but as for pin 2 or 3 to the tip, it doesn't seem to make much difference. I made up an XLR to jack jumper this way and it solved quite a few problems. I didn't make a reversed 2/3 version so can't really compare them.

[sam.spoons]

When hum is a problem then balanced outputs can provide isolation so yes don't use pin 1 on the output device at all. Balanced outputs don't need an earth to work. It's still a bit of a gamble, but as for pin 2 or 3 to the tip, it doesn't seem to make much difference. I made up an XLR to jack jumper this way and it solved quite a few problems. I didn't make a reversed 2/3 version so can't really compare them.

 

Leaving the earth off with a pseudo-balanced output often gives rise to noise issues, leave pin 3 unconnected instead (signal-wise it's effectively the same thing). With transformer balanced you would obviously have no signal if you left pin 3 unconnected but it's better to lift the earth at the input device leaving it connected at the output device.

 

Reversing pins 2 and 3 will reverse the phase of the signal in that cable, this would be unnoticeable if it's feeding the only speaker but if another speaker wired normally is in the vicinity it could give rise to some strange effects.

[IA76]

I'm new to this so some is going over my head but what you are saying is if I had a TRS plug I would wire it like this? http://www.mediacollege.com/audio/connection/XLR-jack-stereo.html

[sam.spoons]

I'm new to this so some is going over my head but what you are saying is if I had a TRS plug I would wire it like this? http://www.mediacoll...ack-stereo.html

 

That link appears to be broken. What specific connection are you trying to make (from what to what)?

[alistermorton]

Link goes to here http://www.mediacoll...ack-stereo.html which redirects to the real page, which you can't cut and paste. Strange.

[mackerr]

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.

 

There is a very good guide to the various ways to make connections with different connectors and interface types HERE.

 

To get the best noise rejection, use regular mic cable (shielded twisted pair), wire the XLR as usual, but connect pins 1 & 3 together in the female XLR, connect pin 2 to the Tip of the TS plug, and connect pin 3 to the Sleeve. Do not connect the shield at the TS end.

 

Mac

[sam.spoons]

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.

 

There is a very good guide to the various ways to make connections with different connectors and interface types HERE.

 

To get the best noise rejection, use regular mic cable (shielded twisted pair), wire the XLR as usual, but connect pins 1 & 3 together in the female XLR, connect pin 2 to the Tip of the TS plug, and connect pin 3 to the Sleeve. Do not connect the shield at the TS end.

 

Mac

 

The Behringer mixer main outputs are (according to the manual) "electronically balanced)", most likely either impedance balanced (cheaper method) or using a single op-amp to invert the signal for the cold signal. Both need cable #3 in the Rane Guide (which I link to in two earlier posts), cable #5 (which you describe above) likely won't remove the noise with an impedance balanced output and may even destroy the op-amp on an electronically balanced output (op-amps don't like their outputs being shorted out which is what that cable does). Only if it's a "cross-coupled" output stage (or transformer balanced) will cable #5 work (see here http://mikeriversaudio.files.wordpress.com/2010/12/balanced-unbalanced_revised.pdf).

 

Link goes to here http://www.mediacoll...ack-stereo.html which redirects to the real page, which you can't cut and paste. Strange.

 

Yes, that's correct for balanced both ends, the issue the OP has is trying to connect a balanced output to an un-balanced input and getting noise introduced hence the different, complicated, answers.

[IA76]

If I had a TRS jack could I also use cable 2 from the Rane guide?

 

Thanks for all the help. .

[sleah]

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

 

Oh what a baffoon I am! Of course it is TS! TIP-SLEEVE! DOH!

[alistermorton]

Something very strange with that XLR cable link ...

[paulears]

So we now have advice to NOT short pin one to either pins 2 and 3 because of the issue with shorting an op amp output, and the advice NOT to lift pin 1.

 

That really helps, doesn't it. I'm a little confused about Sam's advice to lift pin 3 though? Ground on 1 and audio on 2 produces no sound without 3?

 

Confused dot com!

[timsabre]

I'm a little confused about Sam's advice to lift pin 3 though? Ground on 1 and audio on 2 produces no sound without 3?

 

It depends on what the balanced output is.

If it's a mic or transformer balanced output, then you are right, because the whole thing is floating and you need both pins 2 and 3.

However if it's a mixer output, it will work because the pin 2 signal is just an op amp output which will be referenced to ground on 1.

[sam.spoons]

When hum is a problem then balanced outputs can provide isolation so yes don't use pin 1 on the output device at all. Balanced outputs don't need an earth to work. It's still a bit of a gamble, but as for pin 2 or 3 to the tip, it doesn't seem to make much difference. I made up an XLR to jack jumper this way and it solved quite a few problems. I didn't make a reversed 2/3 version so can't really compare them.

 

Leaving the earth off with a pseudo-balanced output often gives rise to noise issues, leave pin 3 unconnected instead (signal-wise it's effectively the same thing). With transformer balanced you would obviously have no signal if you left pin 3 unconnected but it's better to lift the earth at the input device leaving it connected at the output device.

 

Reversing pins 2 and 3 will reverse the phase of the signal in that cable, this would be unnoticeable if it's feeding the only speaker but if another speaker wired normally is in the vicinity it could give rise to some strange effects.

 

So we now have advice to NOT short pin one to either pins 2 and 3 because of the issue with shorting an op amp output, and the advice NOT to lift pin 1.

 

That really helps, doesn't it. I'm a little confused about Sam's advice to lift pin 3 though? Ground on 1 and audio on 2 produces no sound without 3?

 

Confused dot com!

 

As Tim says it does depend on the output topography of the mixer. There are four ways (I think) to achieve a balanced output, explained much better than I could by Mike Rivers here http://mikeriversaud...ced_revised.pdf The cable with the lifted pin 3 (ok, TRS ring in fact as my aux outputs are on TRS jacks but it is the same thing as lifting pin 3) works on my Mackie DL1608 because the cold is simply connected to ground via a resistor (i.e. 'impedance balanced'). It also solves the noise issue where the cable you describe did not. It will also work where a single op-amp is used to invert one of the output signal wires but a cable which shorts pin 3 to pin 1 may cause damage in this case.

 

As you rightly point out (and this had me confused too when I was trying to sold an identical problem with my DL1608) if the outputs are 'properly' balanced with either a transformer or a 'servo balanced' output lifting pin 3 will not work. Sorry for the confusion but it's just how it ishttp://www.blue-room.org.uk/public/style_emoticons/default/blink.gif

[dbuckley]

Fortunately, for most folks with a balanced output mixer needing to link to an unbalanced input, the mixer will be of the cost class that doesn't feature output transformers. :)