Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Nescafe]

Hi All,
I'm new here, and want to ask how do You guys connect balance to unbalance equipment. Not about the cable converter of course, but the electrical circuit.
I have a headphone amp that I really love and want to connect to my working environment but it have an unbalance input, my monitor controller only have balance out.
 
Any input and opinions will be very appreciated.

Thank You.

[klett]

balance output to unbalance input

If the monitor controller uses an electronically balanced output (and it almost certainly does) you essentially have two (small) amplifiers driving each output. These amplifiers drive differentially - meaning one's output is exactly 180 degree out of phase from the other.  One feeds pin 2 of an XLR or the Tip of a ¼" TRS connector and the other feeds pin 3 of an XLR or the Ring of a ¼" TRS connector.  The common or ground would be on pin 1 of an XLR or the Sleeve of a ¼" TRS connector.

In a balanced to balanced connection both "halves" of the differential signal can "swing" up to some point where they clip...  so in a lot of gear that would be somewhere around +20dBu for each half of the differential pair and when you take the difference between the two (which is what a balanced differential receiver or transformer is doing) you get a transmitted level that is 6dB higher or around +26dBu.

An unbalanced input has only one signal input terminal and ground (or common) so you can physically connect balanced to unbalanced a couple ways.  Ground is easy.  Pin 1 of your XLR or the Sleeve of the ¼" TRS at the balanced output can connect straight across to the Sleeve or ground of the RCA (phono) or sleeve of the ¼" TS connector at the unbalanced input.

The two halves of a balanced signal are sometimes called + and - , or hot and cold, or phase and anti-phase... 

Generally the in phase or "hot" or + would be on pin 2 of an XLR or the Tip of a ¼" TRS connector.  That can be wired straight across to the tip or signal pin of whatever the unbalanced input connector is.

Now ...  we are left with the anti-phase or "cold" or - half of the balanced output.  If this were a transformer balanced output then you would simply connect that to the sleeve or ground at the unbalanced input.  You MUST connect both "halves" of a transformer balanced output - both "ends" of the transformer have to be connected to the receiver. 

There are no monitor controllers that I can think of that have transformered outputs except maybe ones that Purple Audio has made... the new one is not out so you it's pretty certain that you don't have that.  Grace, Presonus, all those, anything made that you can buy at Sweetwater, Guitar Center or wherever, will have that active output.

so...  with an active balanced output you don't need to connect that "low" or "-" output at all, BUT you will loose 6dB in level since you are taking only half the differential pair.  This will give you the cleanest connection but you loose 6dB in level and if you have enough gain in your headphone amp you'll just turn the knob up a little more.

If you feel bad about loosing that 6dB you can connect the "low" or "-" pin to ground, either right at the output connector or at the connector on the unbalanced input...   MOST, but not all, active balanced outputs, have a cross connected feedback setup that senses when the low side amplifier is shorted to ground and increases the gain in the high side amp so you do not loose the 6dB.  This would seem to be the way to go but the low side amp is continually driving into ground.  It does not shut off completely.  It does current limit to keep from blowing itself up but in any event that amplifier is still driving some audio to ground in the form of current....  most often this is not "clean" it's distorted. 

In a lot of analog consoles you'll find that the monitor returns for things like tape machines are unbalanced (Trident for example) so if you connect an actively balanced 2 track or DAW to one of those inputs and play it out while you have something else selected you'll still hear a rizzy sort of "bleed" or breakthrough...  THAT is the sound of the low side amplifier driving into ground and leaking all over the monitor section of the console.

so... for directly wired stuff like the connection from your monitor controller to your headphone amp I would drop the low side, deal with the loss of 6dB in level, and have a cleaner connection

hope that helps

[Nescafe]

@klett, Thank You for a detail explanation, but my monitor controller is passive (goldpoints step attenuator) and some switch, so from Your explanation above it's better connect my controller to headphone amp directly (pin 3 not connected) or else? Maybe I need to build an active stage?

Thank You.

[klett]

ahhh...  whole other thing...  and when you said "balanced" output it did not occur to me that you had a balanced passive selector and attentuator...  so in that case you should simply experiment and see what works.  There are variables having to do with what source you have selected to feed this passive controller and other things, so rather than deal with that various theoretical's, I think in this case it's easier to go empirical.

as in previous post I outlined, you really have two options and I think that taking the "low" "-" pin to the ground or sleeve connection at the destination would probably work best in more applications...  so try that..

you know that the "hot" or "+" signal pin from the balanced output should go to the signal pin on the unbalanced destination

you have a couple variations with regard to how the "low" "-" pin at the balanced out and the ground/shield connection from that output that can be tried...  I expect that the ground needs to carry across and the variable is then reduced to connecting the "low" "-" to ground at the unbalanced destination or not...  I suspect it should be connected but honestly it depends on how they did the balanced attenuator and other connections in the monitor controller so...  experiment...

[Jim Williams]

You either need to understand the schematic of the driver circuit or call and talk to the apps engineer at the company that made that piece.

As for grounding the low side of a cross coupled electronically balanced output stage, the linearity of that driver opamp is very important. I've seen TL072's used in Toft consoles that cannot drive below a 2k ohm load without severe THD. Feed a Toft into a 600 ohm transformer coupled comp and you will see a level drop and plenty of grit even if kept balanced.

Even the 5532 will dump plenty of trash on to the ground rails. I found the LM6172 does a pretty good job as it will drive 150 ohm loads, much closer to the actual series resistance that low side opamp is driving. The ability to drive 100 ma of output current makes driving long and difficult loads easier.

If you have a inverted output opamp stage, float that.

[Nescafe]

@klett, got i
@Jim Williams, I just read this post, Thank You, I will remember that if I use the active circuit in my monitoring controller. And are You Jim Williams from Linear Technology?

[John Roberts {JR}]

@klett, got i
@Jim Williams, I just read this post, Thank You, I will remember that if I use the active circuit in my monitoring controller. And are You Jim Williams from Linear Technology?

He would have to be posting from the afterlife, since Jim Williams from Linear technology recently died. We also just lost Robert Pease, another analog great. RIPx2

+1 to what the living Jim Williams said. Some unused active balanced outputs are unhappy when grounded, some unhappy if not. Know which you are dealing with.

JR

[Jim Williams]

@klett, got i
@Jim Williams, I just read this post, Thank You, I will remember that if I use the active circuit in my monitoring controller. And are You Jim Williams from Linear Technology?

Nope, neither am I the guy in Nashville that just passed. I sure got a lot of memorials this week, the only result is I raised my rates. You don't know how hard it is for dead guys to get anything done these days...

[Nescafe]

  Thank's everyone....OOT but do anybody here have recomendation for an illuminated push button? The one with good tactile feel like what Dangerous Music use?