direct boxes and stereo

[Mr_-G-]

Thanks Nordi,
So I take it that a (sub) mixer to reduce all kbds output (unbalanced) cables to just two balanced cables to the main PA mixer still needs a DI box in between?
I thought that a balanced line would avoid noise from lights, long cables, etc. Are you are saying that the sub-mixer would not provide the kind of galvanic isolation that the DI transformers can even if the cable from the submixer to the PA mixer is balanced?

At the moment I use unbalanced cables to the PA mixer and had no problems. It is just that I think it would be useful to have the DI box, but I am not keen on getting one if I do not really need to.

[RedLeo]

if we use a small mixer to mix a couple of kbds, and the mixer has a balanced output, this can be connected to the PA. Is this exactly the same as a DI box?

No , it's not. To elaborate on Nordi's answer: There are two things to consider here, the first being balanced/unbalanced obviously, but the second is Mic level/Line level. Your mixer outputs may be balanced, but they will be Line level outputs, which are not suitable for plugging into Mic level inputs on the main PA mixer. Here, you would need a DI box to reduce the output of your keyboard mixer from Line level to Mic level. The DI box would also further protect your submixer outputs from any Phantom power (as discussed in earlier posts) AND provide the "galvanic isolation" ie protection from ground loops between the two mixers. As you can see, a DI box does a lot of jobs! (There is also the issue of impedances and impedance mis-matching, but that's a problem for another day).

Do mixers have the "ground lift"? (I guess it would be trivial to add it), looking at some circuits.

It's probably not a good idea to mess with the grounding of a mixer. Remember that the mixer has strong and careful grounding, as it can be plugged into a huge number and variety of musical instruments, and any or all of them could have mains power, causing great potential for ground loops and other problems. Mixer designers take this all into consideration, and tampering with it could lead to all sorts of difficulties.

I guess that if the mixer does the job of a DI box, then I would be more inclined to buy a mixer.

As I'm sure you've gathered by now, a mixer doesn't do the job of a DI box, so if you run balanced lines between the two mixers, a DI box (or two) is still neccessary.

At the moment I use unbalanced cables to the PA mixer and had no problems. It is just that I think it would be useful to have the DI box, but I am not keen on getting one if I do not really need to.

Running unbalanced lines from mixer to mixer works, because you are running Line level output to Line level input, so everything matches correctly.

As you see, the whole subject can get pretty complicated, but I think you can understand now that Balanced/Unbalanced is only part of the whole thing.

Just to clarify, if your keyboard mixer has both unbalanced and balanced OUTPUTS, they will all be Line level. However, the balanced INPUTS of your PA mixer will be Mic level, and if it has any unbalanced INPUTS (probably jack sockets), these will be Line level. (This is a generality. There may be other possibilites, but what I have said holds good for most normal situations).

[Mr_-G-]

Thank you.
You have clarified lots of things!