Balanced / Unbalanced?

[ITGITC]

Originally posted by gangsu:

I knew if I tried to get my head around this thread, it would piss me off, and it has.

 

WHY WHY WHY does everyone keep telling me I need a DI.

That's pretty descriptive writing there, Sue. It paints an interesting picture.

 

Why do you need a direct box? Because lots of soundguys are like Donkeys and do only what the've been taught to do or what they've always done in the past.

 

The standard is for keyboards to go through a direct box (or many) - one for each output. This buffers the output and converts it to a signal in the format that the Donkey can use back at his mixing desk. He's sitting there looking at LOTS of microphone inputs and wants to fill them all up with microphones or signals from direct boxes. He doesn't want to have to THINK about fooling with anything else.

 

It's a standard, Sue. That's why you should use a couple of direct boxes (for stereo) when you are performing with a group that is using a professional PA system with a Donkey.

 

Tom

[gangsu]

oh my god.

 

[ITGITC]

Originally posted by gangsu:

oh my god.

 

Hey - YOU are the one who wrote it.

 

I'm just a guy.

[guestuserguestuser.com]

Ha, ha! Yes, Is There Gas In The Car?, that really puts things in perspective! Thanks

 

By the way, may I call you CarGas? for short?

[JeffLearman]

Gangsu, there are 4 issues when connecting audio gear like the stuff we're talking about:

 

1) balanced / unbalanced -- you got that covered.

 

2) hi-z / lo-z -- you got that covered, too.

 

3) level. Your synth is LINE level, the mike preamp is MIC level. Your synth will put out up to 2 volts or more (+4dBu nominal). Mike preamps are made to handle signals in the millivolt range (as low as -60dBV nominal). Most mixers these days can handle it, though, as mentioned above. Some (like Behringer) could clip unless you keep your master level turned about half way down.

 

4) PHANTOM POWER. This is a DC voltage (usually 48V) fed into the micropone by the mixer, to allow the use of electret condenser mikes without requiring a battery or external power supply. (All mixers don't do this, but many do, and some have a switch to turn it off.) This DC voltage is used by the mike, and is easily ignored by the mike preamp. However, it might not be ignored by your synth's output drivers.

 

I don't know what would happen. It might be harmless. It depends on the circuit your synth uses to drive the balanced outputs, and also to some extent the circuitry in the mixer. It's conceivable that both your synth and the mixer would try to drive the same conductor to different voltages, which would generate a lot of current. Eventually one or the other would either hit a current limiter or blow a fuse or burn out a part. One end could hit a current limiter and the other end could blow a part. It might seem to work fine for hours or even days and then POP (much like connecting two outputs together to feed a single input can).

 

I really, really, really, really, wouldn't do it until I was convinced by someone I really, really trusted that it wouldn't damage your synth -- and taking into account the variety of circuit designs that are possible at both ends.

 

One of the things that the direct box buys you is that it eliminates the DC offset of phantom power.

 

Gasman is right, though, that most sound guys keep it safe by not coloring outside the lines. This isn't stupidity or even ignorance, it's merely knowing the limits of your own knowledge. It's surprising how much one needs to know about electronics to safely color outside the lines. Most sound guys are not electronics experts.

[gangsu]

Originally posted by learjeff:

Gangsu, there are 4 issues when connecting audio gear like the stuff we're talking about:

 

1) balanced / unbalanced -- you got that covered.

 

2) hi-z / lo-z -- you got that covered, too.

 

3) level. Your synth is LINE level, the mike preamp is MIC level. Your synth will put out up to 2 volts or more (+4dBu nominal). Mike preamps are made to handle signals in the millivolt range (as low as -60dBV nominal). Most mixers these days can handle it, though, as mentioned above. Some (like Behringer) could clip unless you keep your master level turned about half way down.

 

4) PHANTOM POWER. This is a DC voltage (usually 48V) fed into the micropone by the mixer, to allow the use of electret condenser mikes without requiring a battery or external power supply. (All mixers don't do this, but many do, and some have a switch to turn it off.) This DC voltage is used by the mike, and is easily ignored by the mike preamp. However, it might not be ignored by your synth's output drivers.

 

I don't know what would happen. It might be harmless. It depends on the circuit your synth uses to drive the balanced outputs, and also to some extent the circuitry in the mixer. It's conceivable that both your synth and the mixer would try to drive the same conductor to different voltages, which would generate a lot of current. Eventually one or the other would either hit a current limiter or blow a fuse or burn out a part. One end could hit a current limiter and the other end could blow a part. It might seem to work fine for hours or even days and then POP (much like connecting two outputs together to feed a single input can).

 

I really, really, really, really, wouldn't do it until I was convinced by someone I really, really trusted that it wouldn't damage your synth -- and taking into account the variety of circuit designs that are possible at both ends.

 

One of the things that the direct box buys you is that it eliminates the DC offset of phantom power.

 

Gasman is right, though, that most sound guys keep it safe by not coloring outside the lines. This isn't stupidity or even ignorance, it's merely knowing the limits of your own knowledge. It's surprising how much one needs to know about electronics to safely color outside the lines. Most sound guys are not electronics experts.

ok, so i'm good on 1) and 2).

 

3)is no big deal, that's what volume controls are for.

 

You've got me on 4).

 

to be on the safe side, all i would have to do is take a peek at the microphones in use, jot down the model number, look it up (since I can guarantee I won't recognize what type it is), if they're cheap condenser mics that require the use of phantom powe.... HEY. I can plug a mic into the PM3. I'm assuming a condenser mic. Implying that the PM3 also has built in phantom power?

 

See what happens when I try to think about this stuff?

 

Tell you what. I hesitate to assume anybody's an idiot. That includes myself, and the sound man. So tell me what specific question to ask him re his board. I know i've been told that investigating the facts to avoid the bullshit will rot my mind. .... Hey Zoot, wherever you are.

[ITGITC]

Ummmm,

 

Where did I go wrong?

 

I thought the Donkey analogy would put this topic to rest. but nooooooooo.

 

 

Dear Sue,

 

Purchase two direct boxes and use them when you're in a situation that calls for them.

 

Love ya... mean it!

 

Tom

 

There. That should do it!

[gangsu]

Et tu, GAS?

Why does my idea of simple sound so complicated to the rest of the world? Story of my life!

 

he's already got the box. I just need the cable.

[ITGITC]

Originally posted by gangsu:

Et tu, GAS?

Why does my idea of simple sound so complicated to the rest of the world? Story of my life!

 

he's already got the box. I just need the cable.

I can relate to that, Sue. Everything seems over-complicated all of a sudden. Maybe because it's April 15th and some folks (in the US) are grumpy because they have to pay their taxes today.

 

Most Direct Boxes allow you to use a 1/4" balanced or unbalanced cable from your keyboard to the box. You'll need two for stereo, of course.

 

On top of that, you'll need another pair of 1/4" cables to go from your direct box to your keyboard amp.

 

The sound guy who is providing the box should also provide the proper cable to go from the Direct Box to his mixer.

 

Does this help? Or do I have to get on a plane and come up there and show you - personally? (You DO have airports in the WayBack, don'tcha Sue?)

[Prague]

The IMP 2 does force you to use your ION in an unbalanced output mode. It then converts the signal to a low impedance, balanced, MIC LEVEL signal.

 

The IMP 2 transformer isolates phantom power from the IONs output.

 

The sound guy may do this so that ALL balanced signals can run into his mixer at the same level, into the XLR inputs, and with phantom power.

 

It's a convenience for him and will work fine.

 

Just use 10 feet or less regular cables to the IMP 2 and you should be fine. Let him provide the IMP2's, though.

[gangsu]

Hi. He's got a DI that's all shiny chrome and sits up on rubber feet. Either a good one, or an original model from the 50's, I'm not sure which. I'll buy some 4' cables and let him do his job.

 

Oh. Were you talking to me? I do not have an ION. Or a second job.

 

thanks, all.

[JeffLearman]

There you go, gangsu! That's the attitude. A cheap solution to avoid an argument.

 

To answer your question, the technical question would be:

 

"Are you running phantom power?"

 

If the answer is "no", the question is:

 

"Are you really, really, sure? Can you show me the switch? Actually, here's my volt-ohm meter, gimme that mike cable ... scritch scritch ... YOU SONOFABICHINLIAR! YOU TRYIN TO FRY MY KEYS? !!!"

 

 

Why does my idea of simple sound so complicated to the rest of the world?

Because you're trying to color outside the lines, girl! Don't you know that mixing A's and B's is condemned by the Bible, illegal, immoral, and fattening? Decent people just don't do it!

 

Like I said on another post: I'm looking forward to the day when all our audio is digital wireless and self-assembling. Sound guy fires up his mixer, runs cables to the few antique vintage items we have, but for the rest he just sees the list on his screen and says "OK, play the Zonitron. Good. Now, the Fleebium. OK, got that. Hmm, I see two Snafoobars: Gangsu's and Fred's. Fred, gimme a level on that Foobar."

 

And of course, things won't have changed too much, so the sound guy won't believe we're really playing at concert levels.

 

BTW, we must always have pity on the poor sound guy. If we sound great, nobody notices him. If we sound like crap, he gets blamed. He's the first one there and the last to leave, and he leaves ... alone. Or worse, followed by the geek who wants to finish his point about why discombobulating those fragistats will really help to collectimize the fluximators, which is way cool because ...

 

Now, what was I saying? ... Something about impedance ...

[gangsu]

LOL, you write a good story, learjeff. I do admire the fact that you've managed to get through to me.

 

(truth be told, I can't wait to question him on phantom power. Perhaps I should wait til he's hooked me up.)

[wmp]

Balanced lines and microphones are identical with regard to signal path. Signal ground is supposed to be isolated from chassis ground (shield). Phantom power is delivered to the sleeve (negative) and ring (positive), which ought to be chassis ground and signal ground and isolated from one another. I run phantom power on a Mackie CR1604VLZ with a PC2X, no problem.

 

If the line is unbalanced, then the female connector for the ring should be absent. Should be no problem also. Though I suppose it's remotely possible to short phantom power, which puts the board at risk, not the unit connecting to it.

 

You'll have to try harder if you want to fry your keyboard.

[Prague]

If your keyboard is plugged into the XLR's of your Mackie, then you are applying phantom. Phantom power is only present on the XLR inputs of Mackies (and most mixing boards).

 

Phantom power is applied to both pins 2 and 3 of a XLR connector. If a straight cable with a TRS and XLR connector is made, 48V will be on both the Tip and Ring.

 

Most keyboard audio outputs are cap-coupled, so the phantom would be isolated. However, those output caps may not have a 48V working voltage. There is little reason that they would have more than 10 or maybe even 25V. Damage would ensue.

 

I wouldn't apply phantom to a keyboard.

[gangsu]

Originally posted by wmp:

You'll have to try harder if you want to fry your keyboard.

You've been holding back on me.

I'm able to go directly into Mackie SRM450s. 1/4" balanced TRS to XLR. I know, because it's been done.

I remember having to argue I mean bat my eyelashes for permission from the forum at large to pull that one off, as well.

Is this the same old?

Sheesh

The sound man told me that Mackie's have "blank" built into them, a certain something that the mixing board doesn't. I couldn't make out what particular "blank" he was referring to, he's french, i'm english. He did make it quite clear that the signal would not be strong enough. He mentioned nothing about blowing up my keyboard.

[wmp]

Hmm, I'll take that under advisement until I have time to look it up. I'll assume for now I was repeating bad juju.

 

Thanks.

[Prague]

Those Mackies have an XLR input and an amplifier built into them. You're fine.

 

Maybe he just wanted to see those eyelashes!