Tom Campbell wrote: Does the signal from the direct box stay at the same level regardless of the amplifier's volume level.
The direct box sends the mixer a LOW impedance signal to go over
a long length of cable. It has nothing to do with controlling volume per se. The photo below shows a typical use of a DI.
This is done because you sending a long high impedance signal cable from your instrument to the mixer which might be 100 feet away from you is like to trying fill a swimming pool with a straw. The impedances would not be proper and you would suffer signal loss, at many frequencies.
The direct box still has to go through a preamp section of the mixer. The DI (direct box) just converts your instrument's high impedance signal to
low impedance to get the signal to arrive at the mixer intact.
Results vary as to the quality of sound on the quality of the transformer in your DI.
The Jensens are a standard of quality in DI transformers for pro stage and studio.
You jogged my memory...the direct box drops the impedance.
I'm using my amp as a monitor with the pre-amp going to the mixer board. So if the sound guy sets my guitar at a specific volume level, and I increase the amps volume on my end, I would then mess up his board mix for my guitar?
You would increase stage volume by adjusting your amp but that would depend on what else is going on on stage, what and where are there extra mics.
If you are using ear buds, (I take it these are In Ear Monitors-IEM'S) that would block you from hearing your amp properly and if you turn up the amp you are defeating the overall purpose of earbuds. This means that your being able to hear yourself is a function of the sound person running the PA. In most pro situations there is not only a sound man running the FOH (front of house) PA system there is another soundman/men running a completely separate mixer for stage volume and mixing what each musician hears, who of and how much off to the side of the stage. This involves a more complex system of mixdowns and the mixer used for monitor mixes is a different animal altogether. These are able to provide custom mixes for each person on the stage. Meaning you can choose to hear most of you and less of everyone else or just you, the singer, the bass player, your choice.
If your gigs are sporting spartan PA gear, then a headphone mixer system can be used to give each musician the ability to turn him/herself up or down along with a few other players on the stage.
Without knowing what gear you are using here is a basic idea video of how that would happen.
https://www.youtube.com/watch?v=B_MKUHZKY08
Better
quality ear buds could also help out but basically you need to fight for your right to hear yourself in your buds and if the gear and expertise to achieve that is lacking, then the cliche "YMMV" is the result.
Is it the power amp that determines the volume of the speaker output?
Yes
and no.
Some power amps have volume controls and many do not which means the valve gate or the volume control gas pedal resides in your preamp.
Turning up your preamp that feeds the direct box will most likely change the volume going to the mixer, but that is the soundman's job to fix.
Better solution is run the direct box out of your guitar (after your volume pedal) NOT YOUR PREAMP this way the signal level though the direct box will not change except for your swells from the volume pedal.
Then you can turn your amp up without affecting the level sent to the PA. You would have to do a line check on your volume pedal swells as it appears in the PA mixer. But again it is the soundman's job to be able to mix your instrument such as it is with a volume pedal.
After that it's how your band works with the stage volume and each other on stage to pulse as a unit and a good soundman who knows your music and each song's quirks.
