i have a system that used to have a lot of d.i. boxes in it due to earth loops.{see other thread!!}
now i solved 99% of the problems, and no longer have to use d.i. boxes, mainly due to the fact that i did serious electrical work, and gave every amp and appliance in the system its own independant power line from the same fuse board.


the thing is, on my bigger speakers, i notice a slight humm, or ground noise, when the amp is up full. at no 10 as it were.
but if i turn the amps down to 7, its gone. and i still have loads of power to play with, as it is a thomann t amp3000 i think.

is this normal practice? just turn it down to ger rid of the humm? it sounds grand, its a night club system with loads of power so i can get away with turning down the all the amps to be honest.

or am i being just lazy using this as a quick fix?
thanks again for taking the time to read this.

Edited by xanadu (04/09/09 11:08 AM)

Check again. When you turn the amp all the way up, you're probably hearing hiss, not hum. Hiss is caused by amplifying the movement of electrons in the circuitry upstream of the amp. It can often be reduced by proper gain structure, but you'll probably always have some hiss with the amp turned all the way up.

If it is indeed hum, that would indicate a ground loop. But if you've connected all components to the same fuse board, that shouldn't happen.

thanks for the reply.
where would one find a gain control? the only 1 i came across is on the back of the monitor. i am running thomond t amps and achat speakers , an alen and heath mixer and an ev crossover unit,cant see a gain knob or function on any of these.

Start with the mixer. Let's say you plug a guitar into input number 1. The signal flows through channel 1. At the top of the channel strip (near where you plugged in the guitar), the first thing in the signal path is (usually) the gain knob (called "trim" on some mixers). If you turn up the gain (or trim) too much, you'll overdrive the input amplier (preamp) causing distortion in the signal. If the gain (or trim) is too low, you'll have to amplify the signal somewhere down the line, thereby also amplifying noise in the circuitry. It's important to set the gain (or trim) for every channel so that you're getting a really strong signal from all instruments/vocals, but not too high so as to cause distortion in any of the signals.

Down the channel strip from the gain, you probably have some EQ knobs. If these are turned down all the way, you'll have to compensate by amplifying the signal somewhere down the line, thereby also amplying noise in the circuitry. If the EQ knobs are turned all the way up, you may be overdriving the next stage, causing distortion in the signal. Then there's the fader (slider) for each channel. If these are turned down too far, you'll have to compensate by amplifying the signal (and noise) somewhere down the line. If they're too high, you could be overdriving the next stage, causing distortion. Then there's the main fader which controls the combined signals from all channels. If the main fader is too low, you'll have to turn up the amp, which will also amplify noise. If too high, you may overdrive the amp input, causing distortion. The last thing you want to adjust is the amp volume.

This process is known as gain staging (or setting the gain structure). With a little practice and familiarity with your particular gear, the resulting mix should be relatively noise-free.

thank you so much.

on each strip of eq knobs and vol sliders there indeed is another knob marked "level" this indeed must be a gain,as it is has a direct control on the volume. i wondered why the hell there was another volume control, as this alen and heath mixer already has 2 master volumes.

so gain it muast be.its in the same position across 6 channels . a level knob{which i now take to be gain}.
knobs for high, mids and lows and the slider.