Help: Volume, Master Volume, Trim, Distortio

Subject: Volume, Master Volume, Trim, Distortion
From: UB Ed
Date: 02 Nov 01 - 11:13 AM

This is what I think I know:

On an amplifier, if you have volume and master volume, a high setting on master (with a low setting on the volume)will provide a "clean" signal and a low setting on master (with a high setting on volume) will produce a distorted signal.

This should also apply to an instrument going into a sound board. Trim adjusted right below the peaking level should allow for individual slider volume to be adjusted to any level without distortion. However, individual channel volumes higher than the overall board's master volume will result in distortion.

OK, that being said, what about acoustic instruments with the "on board" electronics? It would seem you would want the volume on the instrument turned all the way up for the non-distorted sound. Except the folks I play with insist that 3/4 is the preferred setting for clarity (And that provides them more flexibility to turn up or down as the situation permits).

So, does the pre-amp associated with on board electronics inherently distort at full volume settings?

Ed

Subject: RE: Help: Volume, Master Volume, Trim, Distortio
From: GUEST,Claymore
Date: 02 Nov 01 - 11:33 AM

It's called "gain staging" and the ideal is to have both the instrument preamp, the trim and the master volumne set within about 25-30% of eachother. As you get to peak output from any given amplifier (or preamp) you start to pick up the inherent noise of that given amplifier. So the idea is to get that stage above the noise floor and safely within the relatively quiet "headroom" of that stage.

If, at any point, you find a real diversion from the ideal, you may have a poorly designed piece of apparatus in that "stage" of the "chain" and you may be forced to compromise to overcome the weakness. With the overlap that each stage gives you, it is often possible to do this, but two poor performing pieces of equipement can take you beyond recovery. Thus, several "magic boxes" or processors may cause you more problems than they are worth.

Subject: RE: Help: Volume, Master Volume, Trim, Distortio
From: UB Ed
Date: 02 Nov 01 - 01:28 PM

Ever reliable Claymore, especially when the question has to do with sound. Thank you.

I assume I am correct in my belief that the trim, channel volume and board volume all behave as amplifiers?

Subject: RE: Help: Volume, Master Volume, Trim, Distortio
From: GUEST,Claymore
Date: 02 Nov 01 - 02:34 PM

In reality they are potentiometers, but they do add to the percieved volume at the end of the chain, which is then sent to the big momma waiting to be tickled (the amp). In simple terms, think of them as bath tubs, each which must be filled to above the "noise floor" (an area at the bottom edge of that particular gain stage) and not too full (above peak, where distorion occurs). By playing with the faders or knobs, you should be able to detect which stage is giving you the noise. If you detect that the offending stage is in a processer in the chain, see if you can remove the noise by dropping the ground out (putting a two prong adapter on the three prong plug) or if the box has a "ground lift" button).

Finally, if that doesn't work, you might want to see about getting a "power conditioner" (a form of power strip that usually mounts over a processor rack with pull out lights etc. - good cheap one come in around $60.). They can be used in place of power strips for sound equipment, and clean up the power, if all your gear is first plugged into them. Properly used, they can clean up about 90% of your noise problems. Good luck!

Subject: RE: Help: Volume, Master Volume, Trim, Distortio
From: Big Mick
Date: 03 Nov 01 - 10:22 AM

Claymore, you are a wonderful Mudcatter. I made a smartass comment to you once, that I regret. Your information is always spot on. You have answered some important questions for me. Long live the Mudcat!!

All the best,

Mick

Subject: RE: Help: Volume, Master Volume, Trim, Distortio
From: Bernard
Date: 03 Nov 01 - 11:11 AM

Earth loops are tricky things, as removing safety earths can cure hum, but could kill you if there's a fault.

For example, you're holding your guitar and your lips touch a microphone. One is plugged into faulty equipment which isn't earthed, the other is plugged into equipment whish is correctly earthed... you become a capacitor between the two. Death can be instant. No joke.

Simple answer? Leave earth loop tracking to those who know what they are doing, or learn about it. An earth loop hum is caused by a current flowing in the earth wire - maybe only a few millivolts, maybe more - and you need to know how it is getting there.

Your best protection is a good DI box with transformer isolation. If used properly, the current then has nowhere to flow.

I'm a professional P.A. engineer, BTW.