Direct out/ Pre Post/ Gnd Lift

[sprocket750]

Hey, I'm a guitar player and used to only playing through low watt tube amps. I joined this group and now playing about 75% bass guitar. I just bought a Orange crush 100BXT for my first bass amp. I'm going to be using it live at a small bar gig in a few weeks and I need to know what the Pre Post/ Gnd Lift buttons are used for when I talk to the sound guy about using the direct out. I assume the Pre Post switch is no eq when on Pre and eq settings when on Post, correct? Not sure what the ground lift switch is for.

 

[Downunderwonder]

The pre is used to take the amp tone out of what goes to FOH.

Ground lift takes away the ground of your amp signal so there is only the mixer ground on that line. Sometimes the amp ground is at slightly different potential from actual ground than the mixer which gives you a ''ground loop'' noise on the line. That gets interrupted with the lift button. Best I can explain with no electrical smarts.

You will probably need your dinky amp up on a box closer to your ears if you want to hear it in a rock band.

 

[sprocket750]

The ground lift seems like a no brainer to take out of the signal to the PA. It would seem to me that would be a default setting and not an optional switch.

 

[lz4005]

I assume the Pre Post switch is no eq when on Pre and eq settings when on Post, correct? Not sure what the ground lift switch is for.

Pre/post: yes. Pre is like having a DI in front of your amp. Post will send your signal with amp EQ settings and any distortion from the preamp to the PA.

Ground lift: leave it off unless there's a buzz when you plug into the PA. If that happens flip it and see if the buzz goes away.

 

[lz4005]

The ground lift seems like a no brainer to take out of the signal to the PA. It would seem to me that would be a default setting and not an optional switch.

In certain circumstances that could get you electrocuted.

 

[sprocket750]

Thanks. btw, I'm only turned up half way on this amp during practice in a basement and it is in most cases too loud. I'm sure it will be different on stage in a small bar but surely it will get the job done along with stage monitors.

 

[JimmyM]

Thanks. btw, I'm only turned up half way on this amp during practice in a basement and it is in most cases too loud. I'm sure it will be different on stage in a small bar but surely it will get the job done along with stage monitors.

While a 100w combo isn't going to be the loudest amp in the world, it should easily be enough for you onstage in a small bar.

 

[bigbri5050]

In certain circumstances that could get you electrocuted.

This was always the risk back in the 50/60's and some people died grabbing a mike or guitar. In those days the mike was litererly connected to the input valva that he 300v D.C. If the insulation went it was a killer! However, now with solid state electronic and the fact that there are Earth Leakage trips on your electrics the risk is minimal. If you are gigging around, make sure that you have an Earth Leakage trip built into each plug the band uses.

 

[agedhorse]

This was always the risk back in the 50/60's and some people died grabbing a mike or guitar. In those days the mike was litererly connected to the input valva that he 300v D.C. If the insulation went it was a killer! However, now with solid state electronic and the fact that there are Earth Leakage trips on your electrics the risk is minimal. If you are gigging around, make sure that you have an Earth Leakage trip built into each plug the band uses.

Not necessary on any amp with a legitimate 60065 or 62368 safety approval.

 

[fdeck]

I wish every bass amp came with a block diagram in the owner's manual. But I drew a crude diagram that should be fairly representative of most amps:

The pre/post switch lets you choose whether the DI output is affected by your tone and volume controls. "Post" means the DI signal will be affected by the tone and volume controls of the amp (and any other effects such as overdrive). In principle, it gives you some control over how your bass will sound coming out of the PA. The drawback is that if you make small adjustments on stage, the PA tech might have to re-adjust their own settings.

"Pre" means that it's more or less straight from your bass. This is my preference, 100% of the time, but YMMV. I don't want a heavily processed sound, and I have to trust the PA tech to make me sound good, because if I don't then they won't. And I want to be able to scoot my volume up and down a bit in order to blend with the band on stage.

Ground lift is more complicated and lets you choose whether the bass amp and PA system share a common electrical ground. The benefit of ground lift is that it can solve some problems with 60-cycle hum if there are other electrical problems in the venue. The downside is that it doesn't solve the underlying problem, which may also be a safety issue in some cases.

About safety issues, I am quite leery of gear and stages in venue, because I can't inspect and critique everybody's gear and setup. I think there are possible scenarios where portable ground fault interrupters are not protective of every possible problem.