Balanced output to unbalanced Input, to Float pin 3 or short pin 3 to Grd?

CoolCat

CoolCat

Well-known member
Just an old revisit relearn.I was confused. I have a Focusrite XLR balanced output of a Rack unit and a 1/4" unbalanced Line IN on the Line 6 interface. No schematics.

Focusrtie tech support says "float" pin 3.
Seems others say "never tie an output to ground!"
While many post around says its ok to short pin 3 to pin1.!!!...which is what confused me.

The Line 6 Tech support replied "do it either way and see what sounds better" pretty much. hmmm?

I went with "floater"...shorting an output to ground sounds too risky.
And its a Focusrite product and they said "float" pin 3 OUTPUT on ISA 430 to my unbalanced interface Line In.
**********************************************************************************************************************
All 3-pin XLR audio connectors (Outputs, Mic/Line Inputs, Insert Send & Return) are wired as follows:

Pin 1: Screen/Chassis
Pin 2: Audio 0°
Pin 3: Audio 180°

For an unbalanced connection you would leave Pin 3 floating. - Focusrite Tech Support
************************************************************************************************
Thanks for reaching out. It shouldn't matter, as the ring connection of the jack is not connected to anything. You can try it both ways to see if one or the other works better for your setup.
All the best, Line 6-Yamaha
*************************************************************************************

The Cable I have, with XLR to 1/4" TS, was opened up at the XLR end and Pin 3 was soldered to Pin 1!!!,
so I snipped it and now Pin 3 is floating.

I guess I dont have schematics for either unit, so I dont know. Seems the Line 6 interface Input is UNBalanced but I dont know with what? Op Amp I assume.
The ISA430 is transformer output BALANCED but there might be something else there too, the above shows there is a signal....180deg ...so doesnt seem right to short it to ground.

Just thought Id post this. Seems Floating PIN 3 is the safe route.
Maybe some volume loss? My line noise is on a desktop so not so worried about that line noise on long runs for this application.
 
If you leave pin 3 disconnected the. Then there is NO audio circuit. If you connect a balanced output to an unbalanced input you have two modes to choose from. If it is a differential or transformer balanced output, you could do the usual thing and connect one of the signal pins to ground. XLR pins 2 or 3 gets connected to pin 1. perfectly fine and normal to do. You are just making the output unbalanced. The XLR pin left is your new signal connection, so that works. You have made a link between grounds of course, and sometimes this can then provide an extra ground path and you get the well known ground loop hum. An alternative exists that offers an alternative. Connect pin 2 to the unbalanced ground connection, connect pin 3 to the unbalanced audio connection. Leave pin 1 unconnected. This is unusual, but works. It also works the other way around where you can feed unbalanced into an XLR input. Ground is for screening, and often isn’t that important for audio, apart from when you need 3 conductors for phantom power.

in your case, I would simply wire the XLR on the output with pins 1 and 3 joined, going to the jack sleeve, and take pin 2 to the tip. Perfectly normal, perfectly safe and the focusrite won’t object. The important thing is that if you make these yourself is to remember using 3 to the tip, shorting 2 to 1 works just as well, but one of each in a stereo connection has inverted one which can give you phase issues in some circumstances. So make any adaptors where you need two or more, exactly the same.
 
Pins 1 & 3 in the XLR are connected because you have a 2 (hot+ground) cable. If you had a 3-conductor cable, those lines would be both attached to ground at the 1/4" TS end, i.e., the negative line "floats" the length of the cable. At least, that's how I understand it. Probably doesn't matter for short runs, but I'd have left it alone.
 
the more I read the less I know..... I recalled and surfed back in time ..

Mark-ARCAXIS of HR, troubleshot my nearly same issue years ago and 1+3 had to be tied together for the LA610 to work right on the same UX/Unbalanced LINE IN.
I tried two cables back then, a floating 3 and a 3 tied to 1...and the 3 tied to 1 worked.
The LA610 worked gorgeously then, where with the wrong cable I thought Id bought faulty unit. So Rob, your note appears to be correct (though I still have trouble understanding..how tying an output to ground? seems odd, like a battery to + to ground or a Speaker + wire to ground is usually a bad bad thing?)

So the ISA430 and LA610 are Transformer outputs, preamps. So tying pin 1to3 seems to be ok, but then why did Focusrite say "float it"...?

This is a very short run, 3ft ish... or less.

A lot of preamps have OP Amp outputs but seems those can be shorted to ground and theres some design for that to be ok, from reading. My APHEX 207 says in the manual it can handle either load, bal or unbal, no worrys, no problem., its nice when they say that for us , less than aware techgearheads.

thanks for the inputs? er.....outputs...
 
The thing is to remember that the one thing about audio is how much level there is - so the hi-fi sort of standard is .775V - guitars are less, so are some keyboards and some pro gear might be even higher, but three quarters of a volt is about where we are. Think back to school. to make current flow, and in our case, audio to travel from source to destination, we need a circuit - two conductors. In DC circuits, we'd say + and -, but in audio it's AC, so for convenience we could just call them hot and cold - as they change polarity so often with a music waveform, plus and minus is just not useful. We often' like in guitar cables, wrap the inner conductor with the outer screen, and that is our two conductors - what we need for audio to pass. In a balanced connection we still have the need for two connections. Pins 2 and 3 provide them. However, this time, neither is used as a shield - pin 1 does that. so it's two conductors plus a screen. In our unbalanced guitar example, the screen does double duty - as a noise screen, and one of the conductors required for the audio circuit. If in the XLR, we attach pin 2 or pin 3 to the pin 1 ground, we've turned it into the guitar connection with shared screen. Strictly speaking, connecting pin 2 or 3 to 1 does actually throw away level. The audio waveform might go up to say, half a volt positive as it reaches the tope of the waveform, but then it might go below zero and go to half a volt negative. This can't happen when it's attached to pin 1, which will be zero volts and ground! Throwing this away reduces the maximum 'swing', but rarely is it of consequence. Balanced XLR circuits usually run at a higher voltage than our 3/4Volt, so it doesn't really matter. Shorting it has no effect on the audio. We're talking such little current nothing happens. Shorting loudspeaker levels and current is a much worse idea - hence why amps have protection.

Does this help?
 
The Rane was great, the Balanced specifically is Transformer LINE OUT, not op amp, Transformer Line OUT, XLR..... to unbalanced LINE IN.

But, Pin 3 to Pin 1 and Pin 2....XLR to 1/4" TS....now I have to solder that cable I just snipped. lol
 
another question on this-

IF IT WERE YOU.....would you

A) mod the wires in the cables to got from Balanced TranOut to Unbalanced Line In 1/4- TS
B) plug the Line Out Balanced Transformer to the MIC IN Balanced (which does have a 20db pad in this case)
 
Well, with a mic cable it would be a ten second job to just try it and see if the output, via the 20dB pad matches? That would be the simplest if you can match the gains. and not require any effort at all.
 
I will try it this weekend. Appreciate all the great inputs.

I re-bought a UX8 because I liked it so much.....but my other Antelope ZENGO has LINE IN "BALANCED" (if a user has TRS 1/4 cable as Line In)
 
There are 3 basic forms of balanced output,
1) 'Proper' balanced where a separate amplifier drives pins 2 and 3 but in opposite polarity.
2) 'Impedance' balanced where only pin 1 is driven and pin 3 is taken to signal ground via a resistance equal to the output resistance driving pin 2, usually around 100 Ohms.
3) Transformer output. This is normally 'floating' on pins 2 &3 so you must ground pin 3 to drive an unbalanced input otherwise there is no ground return and you will get little or no signal. There is a very rare sub-set of transformer where it has a grounded centre tap and in that case do not ground pin 3. I doubt you will ever see such a beast.

Types 1 & 2 are ground referenced to the signal source so you must connect the screen but shorting pin 3 to 1 could damage the drive amp in form 1. Unlikely but the amp will generate high, clipped current pulses and they could be heard. For type 2, please your self.

The advantages of the impedance balanced output, at least for the HR bod, is that it is bombproof and cannot give a polarity inversion, i.e. no cancellation when summed to mono. The system gives as good noise reduction when feeding a balanced input as type 1 and in any case, noise/hum reduction is mainly in the gift of the input amplifier. Downside of course is no 6dB signal boost.

There is a form of bal' out, the "floating balanced servo output". This delivers a full signal even if one output is grounded. Not likely to be seen in anything but very high end gear.

Dave.
 
Dave - I've often wondered about the balance 'pro' level of audio connections, but a 1.4V pp pro level spec device, with one leg grounded is a 3dB loss, making .7V, so is consumer level just a happy accident?
 
rob aylestone said:
Dave - I've often wondered about the balance 'pro' level of audio connections, but a 1.4V pp pro level spec device, with one leg grounded is a 3dB loss, making .7V, so is consumer level just a happy accident?
Click to expand...
I am bit boggled by your numbers Rob? 'Pro' line level aka 'Operating Level is +4dBu or 1.228V *rms =1.736V peak and 3.55V pk-pk. If you freed that from a differential output ignoring the p3 signal you get 6dB less or 0.614V =-4dBV, Some way away from "consumer level" which is taken to be -10dBV =0.316V.

Now, many folks think that consumer level is that which applies to home hi fi gear. Tuner outputs and cassette machine levels. It is not, those devices operate closer to 100mV or -20dBV (some may be at 150mV)

I believe -10dBV 'grew up' with the guitar pedal industry where the maximum output of a pedal powered by 9V is about 3Vrms and so, having 316mV as OP level gives you a 20dB headroom. The guitar amp electronics industry eschewed dBu and uses the far more logical Decibel Volt!

*I have given the figures with quite unnecessary precision in case someone moans!

Dave.
 
I've always used the 1.4V as a figure for +4dBu because of the RMS vs Peak difference - an inaccurate fudge but useful when you give the oft quoted 0.775V. on the 3/6dB front - my fault power was in my head not voltage - the half level when one leg gets grounded was what I was trying to say (badly)
 
Tried all three just now and pin 1 to pin 3 works best in this gear.
Preamp TRansformer XLR Output -Line Out Balanced to Interface Unbalanced 1/4".
Ran Bass guitar in and set the gain, did not adjust, any gain. MicIn was set about mid50% with -20db pad On.
results-
Pin 3 floating was anemic. Mic In XLR could probably be tweaked in some with gain etc... Tied pin 3 to pin 1 was great.

Still dont really understand why, or how come, or whats going on...lol but the ears and signal was pretty obvious!
 

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CoolCat said:
Tried all three just now and pin 1 to pin 3 works best in this gear.
Preamp TRansformer XLR Output -Line Out Balanced to Interface Unbalanced 1/4".
Ran Bass guitar in and set the gain, did not adjust, any gain. MicIn was set about mid50% with -20db pad On.
results-
Pin 3 floating was anemic. Mic In XLR could probably be tweaked in some with gain etc... Tied pin 3 to pin 1 was great.

Still dont really understand why, or how come, or whats going on...lol but the ears and signal was pretty obvious!
Click to expand...
Now I'M confused! Something has a transformer output, what? A traff OP will nearly always require pin 3 to be bonded to pin 1. For instance, any passive microphone* will need that link. Not all mics have transformers in them but still link 1&3.

*However, 'unbalancing' a mic like that will surely cause some hum unless it is a very short run. To go further would need a transformer at the remote end.

Dave.
 
I contacted Focusrite again and made attempt to clarify my question, with this specific unit, that I have no schematics on.
But they said "float pin 3".

This advice doesnt work and actually is a anemic sounding option per my attempt.

Im not even sure the support understands Transformer output or assumes its not Transformer output as most ISA are not transformer output. The 430 mk2 isnt, the newer ISA 428's arent, I think only the 110 reissue has Transformer out., and a few others like the 430mk1. the 428 rev1 do I think.
The ISA One and Two and most all the others dont have transformer on the output, only the input. Mine only has Transformer Output on 1qty Line Out, the otrher Line Out and Digital out doesnt go through the output transformer. So I assume these are IC or Discrete Outputs. ? no schematic or parts lists.

The fear...
Some articles with opamp outputs insinuate tying the output pins to ground can smoke a chip!,
in some cases. I dont know. ...I dont want to risk it.
the old "resistance goes down = current goes up" comes to mind. = smoked...yikes. some seem to say OpAmp outputs have short protection.? idk.

Using the Balanced Preamp XLR out to a Mic XLR balanced In (1.3Kohm) seems the easiest and to feel safe with.
....it the load unit has a pad , seems even better to be a safe bet and easy to grasp mentally and with a standard XLR cable.
It seems as long as the Mic Input doesnt clip theres no real issue.
I might play with the MIC IN XLR Balanced some more. My unit has a -20 pad and I wont worry about shorting any outputs to ground.
Not sure what Impedance effect will be going from a Line IN to Mic In? Line IN 10kohm Mic In is 1.3Kohm on the audio interface.

Reading old posts I went through a lot of this same thing with the LA610 that has transformer output going to Unbalanced Line In, Same results.
arcaxis found the issue...and UA didnt really discuss having the right cable or why, or what to watch out for.

The 430 manual says nothing about hooking up the different outputs to Unbalanced Line In.

oh well...
 
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OK, Let's look as some ways people can find out how their outputs stages are configured in the absence of any schematic.

A digital multimeter will be needed and, if you are AT ALL involved with music technology and don't have one, go and bloody get one!

With the (say) pre amp powered down and if a TRS jack, plug in a short cable.
First check resistance from ring to tip. A few tens of Ohms? You have a transformer OP stage. Now check tip to sleeve. O/C or very high? No centre tap so to feed an unbalanced input you need to connect ring to sleeve.

Not a traff? So check tip to sleeve. Should be a few kOhms like 22 to 100k. Might be infinite in which case the maker has not fitted a DC drain resistor. Bloody poor design that.
If ring to sleeve reads the same as the tip you probably have a 'two amp differential output' but see later.

If ring reads low to sleeve like 100 Ohms or so you have an impedance balanced output.

Active checks.

Feed a sine, 1kHz* say into pre and measure the signal sleeve to tip and sleeve to ring. If equal, diff' amp. If no signal on ring. 'Z' balanced.

Obviously for XLR ring = P3 tip = P2 and sleeve P1.

Re damage and smoke: Should never happen IMHO and I don't know of an op amp that cannot stand a shorted output indefinitely. It will however generate a lot of clipped crap as I said before.
A discrete output stage certainly could be damaged as I doubt the cork sniffing buggers would include protection. I simply don't see the point of discrete stages in such a position? It would take many transistors and cost bunch to even equal the performance of the 40+yr old NE5532 and I doubt anyone anywhere could approach the distortion performance of the LM4562, only THE most advanced test gear shows any distortion. (like 0.002% at 5V rms into 600 Ohms)

*Any DAW can generate sines and other waveforms and noise.

Dave.
 
good morning. yes so DVM, meter, ohmmeter, voltmeter....etc.
I have the Preamp/Channel strip....two XLR Line outputs, one is a Transformer Out and the other is Non-Transformer output.

PREAMP OUT Focusrite-
Pin 1: Screen/Chassis
Pin 2: Audio 0°
Pin 3: Audio 180°

Measurements- No Power

XLR Transformer Out OP1 from pin 2 to 3 = 17 ohm (1 is grd/shield to 2 or 3 is O.L.....which per your info above this is NO CENTER TAP....so needs connect Ring to Sleeve)
Thanks!

On the other output Non-Transformer Post Mic OP.... I get pin 2 tip to 3 ring = 199 k ohm. So this data shows it is fitted with a "DC Drain resistor"
Now pin 1 to 2 is 100k ohm and pin 1 to 3 is 100k ohm.

And which cable is best for this to go to the Unbalanced Line In on the audio interface? Does a shorted OpAmp to ground cause damage?

I havent done the signal test yet. To tell if its Balanced or a Differential Amp? no mention of what kind of cable to use for Unbalanced load gear.

The Manual mentions it is Balanced.

Post Mic OP Connector: XLR Signal: Balanced
Operating Level: +4dBu Maximum O/P Level: +26dBu Signal is routed directly from the Preamp after the gain stage, trim and phase reverse circuits of the input section and can be fed from the Mic, Line or Instrument

OP1 Connector: XLR Signal: Balanced (Transformer)
Operating Level: +4dBu Maximum O/P Level: +26dBu Signal is the transformer output stage.

Thanks for info, something I didnt know.
 
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