General high noise floor troubleshooting

[ricercar.record]

hi, wanted to get some of you knowledgeable folks thoughts/methods/plans of attack on general troubleshooting high noise floor in audio gear. I know that's a pretty general statement but from my limited understanding it seems much more difficult to begin to know where to troubleshoot or start looking in a piece of gear that is operating as it should as far as the main signal path, i.e. no distortion or noise in the signal and all controls functioning as they should, frequency sweeps are flat, appropriate gain, etc. I know that noise as far as a grounding hum can be approached by re-examining your grounding scheme throughout the power supply and audio path, but what about just self noise (hiss) being high. Where would you begin to look for the cause of this issue and how would you approach troubleshooting it with equipment? Apologies for the ignorance, but hopefully I can gain some insight from this excellent resource of people.

 

[sircletus]

Are you talking about a specific piece of gear giving you trouble here? If you are, fill us in!  If you're speaking generally, that's okay too.  But the more info, the better!

 

[bruce0]

Finding noise sources is fun and sometimes nearly impossible!

But sircletus is right, tell us the noise story.

Most important of all is
1) What type of noise?  Is it hiss?  hum? scratching when adjusting things?  Pops or bumps?  Repeated clicking or zinging? A radio announcer telling the weather? Distortion at high levels?
2) What does it sound like? Is it a high hiss, a phase shifting hiss (shw, shw, shw), a coarse sharp hum or a low hum etc.

The reason this matters is the noise itself is your primary diagnostic tool, and can tell you a lot.

For example:  Hiss is rarely sourced from power lines.

 

[JohnRoberts]

All active circuits make noise. That is their natural state. To determine when the noise is excessive requires test equipment and proper methodology (terminated inputs, etc.).  Some relative listening tests, like if one input channel or one bus in console makes more noise than others may indicate a specific problem area, but generally you need to measure against performance specifications.


JR

 

[audiomixer]

high noise floor can also be a sign of a badly adjusted level / gain setup. to much gain in one part and attenuation accordingly somewhere else.

- Michael

 

[ruffrecords]

The frist thing to do is to try to isolate the source. You can do this by turning level controls up and down. If the noise does go up and down when a particular control is operated then the main noise source must be before that level control. If it has no effect then the noise source must be after that level control.

Unless the design is particularly poor, the noise from the input stages will dominate. The other thing you need is a method of measuring the actual noise level in dBu. Sound cards can be used but you do need to calibrate them properly first.

Cheers

Ian