How exactly is the 'sound chain' for live bass set up?

eoinwalsh · #1 06-10-2011, 03:17 PM

I started a thread about DI boxes but I felt that this question should be in a separate thread.

First of all, is this correct ? :

When we use a DI box, we go from the instrument straight into the box. The box is then connected to the amp/head and also separately to the mixer. So the engineer gets two signals : the sound of just the bass going through the box and the sound of the bass after it has gone through the amp/head.

Is that right? If not, please explain the chain to me.

Secondly, if a soundman connects an XLR cable to 'direct out' on the head like on this GK head, this means that a DI is not being used and instead the sound going to the mixer is the sound of your bass through the amp. Is that right?

And finally, if that is correct, does that mean the signal coming from your amp to the mixer via the XLR cable is an unbalanced, high Z signal and is thus more prone to noise?

Thanks very much.

Gearhead17 · #2 06-10-2011, 03:35 PM

When we use a DI box, we go from the instrument straight into the box. The box is then connected to the amp/head and also separately to the mixer. So the engineer gets two signals : the sound of just the bass going through the box and the sound of the bass after it has gone through the amp/head.

Is that right? If not, please explain the chain to me.

If you plug the bass straight into the DI box, the sound guy gets the sound of your bass, not anything else.

Secondly, if a soundman connects an XLR cable to 'direct out' on the head like on this GK head, this means that a DI is not being used and instead the sound going to the mixer is the sound of your bass through the amp. Is that right?

There is a button called Pre/Post on the GK head. Pre means you get the sound of the bass right off the input jack of the GK head - no amp tone. Post means you get the signal of the amp head (your bass tone 100% effected by the amp head's controls).

And finally, if that is correct, does that mean the signal coming from your amp to the mixer via the XLR cable is an unbalanced, high Z signal and is thus more prone to noise?

The signal coming from the XLR cable off the amp head is a low-impedance signal and can easily go 100' without noise or signal degradation.

Hope that helps.

eoinwalsh · #3 06-10-2011, 04:46 PM

That's not quite what I asked.

What I wanted to know was how everything is connected. Is it instrument straight into DI box and then DI box to the amp/head and also separately to the mixer?

And if an XLR cable is connected to the direct out, does this mean a DI box is not being used ?

And if a DI box is not being used in his case, how then can the signal be a balanced, low impedance one ? I thought a DI box must be used in order to get a balanced signal.

Gearhead17 · #4 06-10-2011, 05:09 PM

[quote=eoinwalsh;11025792]That's not quite what I asked.

What I wanted to know was how everything is connected. Is it instrument straight into DI box and then DI box to the amp/head and also separately to the mixer?

Yes. Most DI boxes have a parallel output on them.

And if an XLR cable is connected to the direct out, does this mean a DI box is not being used ?

You could have a DI box before the amp and use the XLR out on the amp head for two DIFFERENT signals if you wanted. You can send one DI box signal from the instrument before the amp, and then send another signal from the amp head. That would be two channels of sound sent to the mixer board via two XLR cables. You have two live signals right there.

If you already have the DI box in front of the amp, you do not have to use the Amp head XLR out. A separate DI box is generally used because it sounds better than the amp DI, the amp's coloration is not needed for the signal, or the DI you want to you use has it's own pre-amp.

And if a DI box is not being used in his case, how then can the signal be a balanced, low impedance one ? I thought a DI box must be used in order to get a balanced signal.

You can plug some part of your rig into a microphone pre-amp which should allow you to send an low-impedance and balanced XLR signal out of it. You can plug that straight into the stage snake and the sound guy will have it at his mixer board.

eoinwalsh · #5 06-10-2011, 05:14 PM

Very good. Thank you.

Gearhead17 · #6 06-10-2011, 05:14 PM

No problem.

uhdinator · #7 06-10-2011, 07:06 PM

Think of the DI box as a Y cable. It sends the instrument level out uneffected to the amp and a balanced low impedance mic level to the mixer via an XLR cable.

DI outs on amps are effected by pre amp level and EQ of the amp and are balanced XLR also. Amp DI's can cause ground hum issues sometimes and a DI box before the amp usually does not have that issue. Some sound guys prefer DI box as it eliminates level and EQ issues caused by you fiddling with amp settings as well.

Components in amp DI circuits are sometimes not as high quality as a good DI box as well.

JohnMCA72 · #8 06-10-2011, 09:13 PM

You can mix & match signals in a variety of ways. Most common (at least in my experience; YMMV) is to put the DI ahead of everything except a tuner in the chain from the instrument to the amp. That sends a clean, dry signal to a channel of the console. Another option is to put the DI after any effects, but ahead of the amp.

So far, the only signal sent to the PA is from the DI. However, sometimes the amp will be mic-ed as well, with 2 channels sent to the console. 1 channel is dry (no effects, no amp/speaker "coloring" of the tone, etc.) & the other has all of the effects & coloring that the amp puts out. The mixer can manage the 2 signals however they need to, to get the end sound that they want in the final mix. That sort of thing usually only happens in very high-end gigs.

So, the answers to your questions, as is so often the case, is "It depends."