Another question... Unbalanced on a Balanced....

[SFM-Ptgal]

Alright... What If I connect an unbalanced domestic Sony cd player to a balanced 600 ohm input of the console? Should I take care with something?

Thanks!

 

[ChiefEngineer]

Outputs are problems into inbalanced on some consoles (like Wheatstone and some others) but inputs don't usually create issues.

 

[CW]

Alright... What If I connect an unbalanced domestic Sony cd player to a balanced 600 ohm input of the console? Should I take care with something?

Thanks!

MOST if not all currently produced consoles are NOT 600ohms...that went away in the 80s...they use active balanced inputs (read that as OP AMPS)...and the input is more like 20K Ohms....hooking an unbalanced output to a balanced input will not be a problem. Hook the center or hot of the unbalanced to the + of the console input..leave the - floating...tie the grounds/shields together...IF you are worried about audio ground loop, etc, get a 8ohm to 1k ohm transformer from Radio Shack...hook one side to the unbalanced hot and ground...(preferably the 1K side), then hook the other side to + and - of the console and leave the shield/ground floating (YES I said that right)...
YOUR levels will be the biggest issue....consumer gear is -10dbm....professional is +4dbu.....BUT with one lead open (in this case, the - lead if you connect direct), the input can be driven at about -6dbm ok....so the -10dbm willl be a little low but will work ok..Pro consoles are ALL unbalanced inside...the active balanced is created by op amps today and not transformers....on the input, one opamp inverts the (-)in polarity and then another one combines + and the inerted -....
on the output, the unbalanced signal splits to two opamps..one is non inverting, the other is inverting and creates the - signal. If you tied just to the + and shield/ground, it would be pretty much a consumer board....there is NO balanced audio INSIDE the unit.....its only done when connecting to the outside (to prevent hum pickup). To hook a BALANCED signal to an UNbalanaced INPUT, you leave - floating and connect + to HOT or center and Shield/GND to unbalanced ground...you MAY be a little hot but it will be ok...(maybe 4db at max hot if you keep the console at 0VU)

 

[Chuck]

The real problem will be low level. Most unbalanced consumer devices have a nominal output level of -10 dbm. Professional balanced equipment is usually engineered for +4 dbm, a 14 db difference. If the console does not have enough gain, it may not be a happy marriage. Impedance matching may be another issue. You can usually go from a low impedance output to a high impedance input with no problem. Going from high to low creates distortion and usually a drastic roll-off of bass response. The wild card is not all balanced inputs are really low impedance. You'll just have to try it to see if it works OK. If not, there are a variety of matching devices out there. Henry Engineering, Peavey and a lot of others make -10 to +4 converter boxes.

 

[CW]

The real problem will be low level. Most unbalanced consumer devices have a nominal output level of -10 dbm. Professional balanced equipment is usually engineered for +4 dbm, a 14 db difference. If the console does not have enough gain, it may not be a happy marriage. Impedance matching may be another issue. You can usually go from a low impedance output to a high impedance input with no problem. Going from high to low creates distortion and usually a drastic roll-off of bass response. The wild card is not all balanced inputs are really low impedance. You'll just have to try it to see if it works OK. If not, there are a variety of matching devices out there. Henry Engineering, Peavey and a lot of others make -10 to +4 converter boxes.

The +4dbu only if both + and - of the active balanced line is connected...when only one lead is active, the level drops to about -6dbuor so...plenty with consumer levels of -10dbm....ALSO consumer gear is HIGH Z out....input to the pro gear is 20K or high Z...not a problem...going the other way, the LOW Z out of the active balanced pro gear is a voltage source and not a power source (IE Xfmrs/600ohm etc)...driving the consumer High Z input with an output off the Pro gear (only using ONE hot lead, either + or -) will work fine with NO freq response problems..been there, done that...NOW with a POWER matched network (600ohms source or termination), there could be an issue....
Remember, ABC Radio Networks designed the ACTIVE balanced circuit in the early 1980s to get around these issues with 600ohm balanced lines. With HIGH Z inputs, low Z outputs and voltage sourced instead of power sourced, the issues are gone...

 

[Info-warrior]

MOST if not all currently produced consoles are NOT 600ohms...that went away in the 80s...they use active balanced inputs (read that as OP AMPS)...and the input is more like 20K Ohms....hooking an unbalanced output to a balanced input will not be a problem. Hook the center or hot of the unbalanced to the + of the console input..leave the - floating...tie the grounds/shields together...

I've always been told to tie shield and negative together, otherwise, you'll get reduced level. That's the way I've wired my console (Behringer). Is this a practice only used with 'semi-pro' gear?

 

[CW]

I've always been told to tie shield and negative together, otherwise, you'll get reduced level. That's the way I've wired my console (Behringer). Is this a practice only used with 'semi-pro' gear?

No it is not and it COULD damage your gear if done on an output....
The + and - leads are merely 180degrees out of phase...connecting either one to shield/ground does NOT change the level in any way on an input (It would be like shorting one side of a balanced transformer to ground) BUT it doesnt cause any damage since it is an input to an opamp and thus you merely are tying it to ground (HOW that would raise levels, I want someone to explain it to me...35years in the biz and "I" sure can't see it BUT doing do on an OUTPUT will cause that hot lead (+ or -) to be a dead short to ground..and this could damage the opamp in that circuit (some are more forgiving than others but they are still outputting into a dead short)...NOT A GOOD THING!....NEVER NEVER NEVER tie either hot lead to Ground!!! Always let the unused float!!!

 

[littlejohn]

Let's change that lst to 'never tie a leg to ground on equipment with active balanced outputs.' If the oputput is transformer balanced - like the Premium Line ITC machnes just to pick one, you will have to tie one leg to ground. As someone said above, be careful with outputs, and know what the topology of the equipment is before you hook it up.

 

[gtomas]

As somebody already mentioned, power transmission requiring impedance matching (like 600 Ohms) has long been abandoned in the audio industry. Voltage transmission is what I'll dare to say all audio manufacturers use today and have been for quite a few decades. In voltage transmission source impedance is low, while the input impedance is high producing no voltage loss on the line. As long as the input impedance of the audio input is reasonably high (>10k), you don't have to worry about impedances...

Going back to balanced and unbalanced connections, just a tiny correction - the level difference between consumer and professional equipment is not 14dB, but actually 12dB. That's because standard consumer level of -10dBV is referenced to 1V and professional +4dBm level is referenced to 0.775 V.

If you're connecting unbalanced audio output to balanced audio input, my advice would be to wire the signal lead to + balanced input and ground lead to both - balanced input and ground. As CW pointed out, you can do this only for inputs (that is tieing - input and ground together) which I believe is clear to anyone doing audio wiring. Or at least it should be! You have to have at least some basic understanding of audio and what you're doing...

You can leave the - input floating, but there's couple of problems with it. You're loosing all CMMR capability of the balanced input, the - input can pick up noise and interference that would than appear in the audio and lastly, some manufacturers don't even use ground as a reference for balanced input (as it is not necessary) especially if there's a transformer on the input.

So, the best way that I would suggest (short of putting a high-quality transformer at the input) is to use a shielded twisted-pair cable, connect the hot wire to the signal lead on the consumer's equipment audio output, tie cold wire and shield together and connect them to ground lead on the consumer's equipment audio output. Wire as usual on the balanced input (hot pin 2, cold pin 3, shield pin 1).


Regards,
Goran Tomas

 

[fm-engineer]

I've always been told to tie shield and negative together, otherwise, you'll get reduced level. That's the way I've wired my console (Behringer). Is this a practice only used with 'semi-pro' gear?

No it is not and it COULD damage your gear if done on an output....
The + and - leads are merely 180degrees out of phase...connecting either one to shield/ground does NOT change the level in any way on an input (It would be like shorting one side of a balanced transformer to ground) BUT it doesnt cause any damage since it is an input to an opamp and thus you merely are tying it to ground (HOW that would raise levels, I want someone to explain it to me...35years in the biz and "I" sure can't see it BUT doing do on an OUTPUT will cause that hot lead (+ or -) to be a dead short to ground..and this could damage the opamp in that circuit (some are more forgiving than others but they are still outputting into a dead short)...NOT A GOOD THING!....NEVER NEVER NEVER tie either hot lead to Ground!!! Always let the unused float!!!

On the old A500 Wheatstone they recommended shorting - to ground when driving unbalanced sources. It depends on the configuration of the op amps. In most cases, you never short them, just leave the - floating.

 

[cgould]

MOST if not all currently produced consoles are NOT 600ohms...that went away in the 80s...they use active balanced inputs (read that as OP AMPS)...and the input is more like 20K Ohms....hooking an unbalanced output to a balanced input will not be a problem. Hook the center or hot of the unbalanced to the + of the console input..leave the - floating...tie the grounds/shields together...

I've always been told to tie shield and negative together, otherwise, you'll get reduced level. That's the way I've wired my console (Behringer). Is this a practice only used with 'semi-pro' gear?

I have always tied the (-) lead of a balanced INPUT to ground / shield for unbalanced gear.

1) Less chance of picking up noise (especially if there is any RF floating around)

2) I've run into many situations where you get an increase of level on that channel (probably due to the use of simpler OPAMP balanced input
circuitry). Yes, technically there should NOT be a difference in level, but depending on what games they play with their particular scheme, you CAN notice an increase in level by grounding the (-) INPUT...

-C

 

[RadioFixerCLE]

I have a balanced output from a processor going into a consumer line-in of a domestic amplifier.

The way I made the cables was this: Live and return connected as normal. Leave shield floating at the RCA plug end. Works fine...but I wonder if that can be a problem.....

I admit this whole balanced/unbalanced connection thing confuses the daylights outta me (newbie). :-[

 

[greg.hahn]

I have a balanced output from a processor going into a consumer line-in of a domestic amplifier.

The way I made the cables was this: Live and return connected as normal. Leave shield floating at the RCA plug end. Works fine...but I wonder if that can be a problem.....

I admit this whole balanced/unbalanced connection thing confuses the daylights outta me (newbie). :-[

Stephanie just remember that balanced lines are an innovation of many years ago and were created by using transformers on all outputs and all inputs. They are very immune to noise that way, but good transformers are expensive, and all transformers are heavy and bulky.

When they started using op amps in audio equipment it all changed. An op amp has an unbalanced output, but if you take a second op amp off the output of the first one and invert it, you have a nearly identical output that is opposite in polarity. So if you use the first op amp for your + connection and the second one for your -, you have sort of the same thing as that old transformer balanced output, with one big exception: the transformer was completely happy with having one of it's terminals grounded. But grounding the output of an op amp is not a good thing!

You can use something to monitor the outputs with respect to ground and see if the + output to ground and the - output to ground have the same amount of signal at a decent level. (Use a telco butt set, or high Z headphones, or an AC voltmeter.) If they do, you have an active-balanced output as I described above, and you don't want to ground either side. The solution is to remove the wire from the - output and connect it to ground.

Now for the original question posed by SFPTgal: Connecting your Sony CD players to a 600 ohm balanced input is not the best solution, but I've seen it done and it does work without hurting anything other than your performance. If you're using a board like an Autogram IC-10 you can probably jack up the levels on the board and get away with it.

The best solution would be to get a Henry Matchbox to go between the CD player and the board. But the Matchbox probably costs more than the CD player did to begin with.

I assume you are in a low budget situation or you wouldn't have asked the question to begin with. So just go ahead and hook it up and see how it sounds. You'll probably be just fine.

 

[speakerman]

These are hard to beat http://www.jensen-transformers.com/iso_aud.html . I always feed in a 300 Hz square wave and put a an adjustable pot across the input while monitoring on a scope. Adjust the pot for best square wave shape with no overshoot. Pull out, measure and replace with a fixer resistor. Sometimes you need to build-out the the source feed to the transformer to get the best match. Clean and quiet end result. A lot depends on the length of cable between the source and destination.

 

[speakerman]

I missed a 0 on the test frequency in the last post. It should be 3000Hz rather than 300. I didn't do a preview before posting.
More coffee needed please.

 

[Studio1]

Alright... What If I connect an unbalanced domestic Sony cd player to a balanced 600 ohm input of the console? Should I take care with something?

Thanks!

YOUR levels will be the biggest issue....consumer gear is -10dbm....professional is +4dbu.....

As I believe it, consumer levels are -10dBV and pro levels are generally +4dBm.

 

[CW]

MOST if not all currently produced consoles are NOT 600ohms...that went away in the 80s...they use active balanced inputs (read that as OP AMPS)...and the input is more like 20K Ohms....hooking an unbalanced output to a balanced input will not be a problem. Hook the center or hot of the unbalanced to the + of the console input..leave the - floating...tie the grounds/shields together...

I've always been told to tie shield and negative together, otherwise, you'll get reduced level. That's the way I've wired my console (Behringer). Is this a practice only used with 'semi-pro' gear?

I have always tied the (-) lead of a balanced INPUT to ground / shield for unbalanced gear.

1) Less chance of picking up noise (especially if there is any RF floating around)

2) I've run into many situations where you get an increase of level on that channel (probably due to the use of simpler OPAMP balanced input
circuitry). Yes, technically there should NOT be a difference in level, but depending on what games they play with their particular scheme, you CAN notice an increase in level by grounding the (-) INPUT...

-C

Didnt say you couldnt do it..I HAVE tied the - lead to ground in a lot of cases for the reasons you posted....
BUT INCREASE IN LEVEL?? No way thats possible...you are grounding the input of an inverting op amp..thus no signal flow..
(the - input is only inverted 180degress and then added to the + input NON inverted audio internally) IF you saw level increase. something is NOT wired right...a GROUND short on the - lead should not cause any additional level input...on active or transformer inputs for that matter!

NOW in BALANCED use. you should only attach shield to the equipment at the SOURCE and let shield FLOAT at the Termination....(notice I said balanced use...NOT unbalanced)...Shield on active balanced is NOT a ground return...and only acts as a RF/Noise shield but CAN lead to a ground loop hum issue if every shield is tied at INs and OUTs....(I KNOW! I had a studio that drove me crazy because of that..I inherited it..when we changed the console out and went from a PR&E BMXII to a RMX28, EVERY shield into the RMX was left floating...and shields OUT were connected ONLY at the RMX...HUM went away and I was happy same principle behind using Cat5 in studio wiring...shield is no longer a real audio ground.

 

[CW]

I have a balanced output from a processor going into a consumer line-in of a domestic amplifier.

The way I made the cables was this: Live and return connected as normal. Leave shield floating at the RCA plug end. Works fine...but I wonder if that can be a problem.....

I admit this whole balanced/unbalanced connection thing confuses the daylights outta me (newbie). :-[

Steph, ACTIVE balanced is merely an out of phase push pull circuit. With transformers, one of the "outside" leads of the xfmr could go to ground with little issue....as the cicrcuit was totally floating due to transformers on both ends....a ground on one side did not cause any issue (maybe a hum if there was ground loop problem already)....
Active balanced use opamps to create the balanced circuit....the + and - are the same lead; just 180deg out of phase with each other. (The + is inverted by an opamp thus creating the - lead..there is some microscopic time delay between the two but in analog audio you wont see it in short cable runs...maybe if the thing ran for MILES...but doubt it).

In your case, you should have the hot or center lead of the RCA cable going to + and the shield of the RCA cable going to SHIELD at either end of the pro gear...ON THE input to the pro gear, you CAN tie - and shield together...but NEVER tie an output to GROUND or SHIELD...remember, in active balanced, there is no real RETURN..(heck Ive been in the biz for 35 yrs and its still confusing to me..but hey it works

Active balanced is like unbalanced if you disregard the - lead and, inside pro gear, guess what......its 100% unbalanced! The "balanced" is only used when outside the box; this was done to allow active balanced devices to interface to legacy transformer circuits with no issues but mimnimize hum while making gear easier to design.....(actually you can use + or - as a hot lead output to an unbalanced input...but you want to stay consistant with wiring...eventually you may end up with an out of phase issue...and that will really drive you nuts!) you COULD almost wire a studio as totally unbalanced..(Ive seen it done)...but you do expose yourself to possible issues.

I have driven a telco dry pair (not a POTS line) directly from a console output with no problems...one jerk engineer though (who thought he knew everything because he used to work for Pacific Bell as a cable man...big whoop) and works for a California group, argued with me that it needed eq and impedance matching...MAYBE back in the days of LONG cable connections and BC gear being 600 ohm transformer out....but in the modern world (post 1980s), that doesnt hold true...
1) The voltage source opamp is LOW Z out (almost zero) and will drive ANY load without loss of freq response or level
2) the telco cable maybe runs for a couple of hundred or thousand feet..then hits a mux hut or SLIC cabinet or DSLAM or something that then converts it to T1/fiber...so I am gonna worry about EQing that??? I doubt it......After that its likely fiber many miles to the xmtr site where it drops back to copper for maybe a mile, at the most...Sorry, in the OLD days, he may have been right but the jerk refused to listen and it almost came to fists (I dont like it when a jerk is screaming at me about something he WRONG about...and I do telecom work as well...more than he does)....luckily I dont work with that idiot anymore..might have thrown him off the tower someday (and...........would have made a lot of people happy if that had happened =

 

[cgould]

Didnt say you couldnt do it..I HAVE tied the - lead to ground in a lot of cases for the reasons you posted....
BUT INCREASE IN LEVEL?? No way thats possible...you are grounding the input of an inverting op amp..thus no signal flow..
(the - input is only inverted 180degress and then added to the + input NON inverted audio internally) IF you saw level increase. something is NOT wired right...a GROUND short on the - lead should not cause any additional level input...on active or transformer inputs for that matter!

NOW in BALANCED use. you should only attach shield to the equipment at the SOURCE and let shield FLOAT at the Termination....(notice I said balanced use...NOT unbalanced)...Shield on active balanced is NOT a ground return...and only acts as a RF/Noise shield but CAN lead to a ground loop hum issue if every shield is tied at INs and OUTs....(I KNOW! I had a studio that drove me crazy because of that..I inherited it..when we changed the console out and went from a PR&E BMXII to a RMX28, EVERY shield into the RMX was left floating...and shields OUT were connected ONLY at the RMX...HUM went away and I was happy same principle behind using Cat5 in studio wiring...shield is no longer a real audio ground.

Yes, you are right...if the balanced input is built as you describe...which is the proper way to do it. I've run into many "cheap and dirty" active balanced inputs (rarely used in pro gear, but all over the place in semi-pro gear) where a single opamp stage is used as an active balanced input. In this case, grounding the non-inverting side of the op-amp stage does increase the level you get on that channel input when using unbalanced gear.

I just threw that out there to back up what a previous poster heard about that same trick...I've observed this myself on some gear.

-C

 

[cgould]

....I forgot to post that you are also right about the polarity thing. Grounding the (-) side won't change the level...but grounding the (+) side will - if the input stage is a simple single op-amp active balanced input stage....

Be aware that using the (-) input as the "hot" side will also flip the polarity of the audio too...

-C