Hi everyone,

Would there been any reason why I couldn't use this for my monitor mix? I plan on using one of these for my FOH mix but would like to add one as well for the monitor mix.
http://www.sweetwater.com/store/detail/CleanBoxII

We recently got a new bass player and unfortunately his bass puts a loud hum in to the monitor mix, I am assuming I got some sort of ground loop going and haven't been able to peg down the problem, the FOH mix handles it very well and hardly noticeable but I am not sure what I can do for the monitor mix. I am already running him through a DI-box and that doesn't seem to help much.

Quote JordanE:

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We recently got a new bass player and unfortunately his bass puts a loud hum ... I am already running him through a DI-box and that doesn't seem to help much.

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The CleanBox II is just a couple of transformers in a box, and it's used to break the ground path between input and output which will prevent a ground loop being formed in that signal path (there may be other paths that still create ground loops of course!).

If you already have a DI box between the bass and the rest of the system -- and that DI box has it's ground lift function enabled -- then your problem isn't from a ground loop involving that source.

It may well be that you have other ground loops in your system, but scattering CleanBox IIs about the place isn't a very sensible approach. It may appear to cure the problem if you're lucky, but you'd be much better off finding out where the source of the problem lies and dealing with it more coherently.

I'd suggest starting out by rigging your PA system and the FOH desk and making sure that is hum free, then conect your stage sources, checking as you go, and then do the same for the monitors and monitor, and then the sources.

Hugh

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Technical Editor, Sound On Sound

Thanks for that, I will keep checking and try to find the source of it. As it stands now when I mute the bass guitar channel are hum just about completely stops, Like I said the main mix is fine but the second monitor mix is pretty much unusable due to the bass player. We are running a DI-Box and I do have the ground lift switch engaged.

The only thing I have not tried is changing cables out, I do not have any cables that will do the job laying around at the moment.

Is there no bass amp on stage, and/or is the monitor mix for in-ear monitoring?

Otherwise, bass guitar is seldom needed in the monitoring chain. This is because bass frequencies are not directional, meaning that they can be heard about equally well anywhere. Except if the band is using IEM, of course... Or if the stage is very large, and then you would need decent size stage monitors to be useful for any bass.

Clean audio begins by sorting out a clean mains power supply. For small venues, I usually try to have all audio electronics powered from a single socket in a "star" topology. 16A goes a long way to power a rock band in a pub! If the backline, FOH and monitor amps are drawing power from separate sockets, then you can expect to have ground loops. If your rig trips the circuit breaker, then use two sockets on separate circuits but try to stay on a single phase. For drawing more than 32A, I would want to see the building technician and plan for a 3-phase mains supply.

When possible, the phase you use for audio should be separate to the phase for the lights. Real world situations means you probably won't know if this is the case in advance. Try to "sound check" dimmed lights before sound checking the band, as you may find you have to reroute power cables. (Dimmer packs make the most noise on the mains when the lights are dimmed to about 20%.)

Other notorious "power pollutants" are bar fridges and restaurant kitchens, which will use power from all three phases. This you will rarely have a chance to find out before the show begins. That's all part of the charm.

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cheers,
t-:

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Is there no bass amp on stage, and/or is the monitor mix for in-ear monitoring? Otherwise, bass guitar is seldom needed in the monitoring chain. This is because bass frequencies are not directional, meaning that they can be heard about equally well anywhere. Except if the band is using IEM, of course... Or if the stage is very large, and then you would need decent size stage monitors to be useful for any bass.

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No bass amp on stage, using couple of wedge monitors. This is good to know, I will just take him out of the monitors from here on out.

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Clean audio begins by sorting out a clean mains power supply. For small venues, I usually try to have all audio electronics powered from a single socket in a "star" topology. 16A goes a long way to power a rock band in a pub! If the backline, FOH and monitor amps are drawing power from separate sockets, then you can expect to have ground loops. If your rig trips the circuit breaker, then use two sockets on separate circuits but try to stay on a single phase. For drawing more than 32A, I would want to see the building technician and plan for a 3-phase mains supply.

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I have two power amps, one is powering the mains and the other is powering the monitors, both amps are plugged in to a power conditioner and being pulled from the same socket.

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When possible, the phase you use for audio should be separate to the phase for the lights. Real world situations means you probably won't know if this is the case in advance. Try to "sound check" dimmed lights before sound checking the band, as you may find you have to reroute power cables. (Dimmer packs make the most noise on the mains when the lights are dimmed to about 20%.)

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Yup, we have about 10 of those dimmer lights and I noticed that it adds some hum to the headphones when I am monitoring but I do not hear it in the main mix.

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Other notorious "power pollutants" are bar fridges and restaurant kitchens, which will use power from all three phases. This you will rarely have a chance to find out before the show begins. That's all part of the charm.

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Kitchen behind the stage but that shouldn't affect anything unless I have equipment down there plugged in, which I don't.

Quote JordanE:

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JordanE Quote:

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Is there no bass amp on stage, and/or is the monitor mix for in-ear monitoring? Otherwise, bass guitar is seldom needed in the monitoring chain.

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No bass amp on stage, using couple of wedge monitors. This is good to know, I will just take him out of the monitors from here on out.

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I didn't mean to say that only having the bass in the FOH mix is sure to be satisfactory for the musos on stage. To get a good groove, you must ensure that the drummer and the bass player can "lock into" each other: they need to hear each other well. The FOH will let them hear the bass fundamentals, but they will have trouble hearing the overtones of transients which are important for keeping tempo. The DI you have for the bass guitar should have a parallel-out jack, and an easy fix is perhaps to feed this signal to a bass amp in the backline.

Quote JordanE:

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I have two power amps, one is powering the mains and the other is powering the monitors, both amps are plugged in to a power conditioner and being pulled from the same socket.

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Everything else, like the mixer and an extension cable feeding mains to the gear on stage, should also be getting juice from the same socket. Then you will have eliminated the most common reason for ground loops.

Quote JordanE:

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Yup, we have about 10 of those dimmer lights and I noticed that it adds some hum to the headphones when I am monitoring but I do not hear it in the main mix.

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Do the dimmers add noise to the monitor wedges? You may want to try using a different socket (phase) for the lights. Having access to an electrical diagram of the building would be useful for this.

A very useful gadget for your tool kit is a socket tester, to check that the power sockets have proper wiring of earth, neutral and live. This tool can save lives, as well as expose sources of hum!

It seems that you have the luxury of staying in the same venue, then you could take your time to experiment with different configurations. There is no better teacher than good old trial and error.

--------------------
cheers,
t-:

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I didn't mean to say that only having the bass in the FOH mix is sure to be satisfactory for the musos on stage. To get a good groove, you must ensure that the drummer and the bass player can "lock into" each other: they need to hear each other well. The FOH will let them hear the bass fundamentals, but they will have trouble hearing the overtones of transients which are important for keeping tempo. The DI you have for the bass guitar should have a parallel-out jack, and an easy fix is perhaps to feed this signal to a bass amp in the backline.

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His AMP is stilling right their and I was thinking of doing that, until I can get a better stage mix going. I will do that on Sunday and see how it goes.

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Everything else, like the mixer and an extension cable feeding mains to the gear on stage, should also be getting juice from the same socket. Then you will have eliminated the most common reason for ground loops.

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Fantastic tip! I will definitely check in to that and make sure that they are.

Quote:

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Do the dimmers add noise to the monitor wedges? You may want to try using a different socket (phase) for the lights. Having access to an electrical diagram of the building would be useful for this.

A very useful gadget for your tool kit is a socket tester, to check that the power sockets have proper wiring of earth, neutral and live. This tool can save lives, as well as expose sources of hum!

It seems that you have the luxury of staying in the same venue, then you could take your time to experiment with different configurations. There is no better teacher than good old trial and error.

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As far as I am aware there is no noise to the monitor wedges that the dimmers adds, the main mix has a tid bit and I mean just a tid bit when things are up really loud. Like I said I only notice it in the head phones when I am monitoring.

Will do some research on that tool and may pick one up. I do have the luxury of staying in the same venue, but how they originally set up the system and cut corners and not to mention my lack of experience in this field, makes it extremely difficult..