A Question About HUM

[GLM]

Do you have a DMM? Did you measure the AC voltage at the socket with all the equipment turned on?

Unfortunately I dont.

 

[Cqwet Dbdfte]

Unfortunately I dont.

The Brymen BM869 should give you microvolts sensitivity. Not expensive.

 

[Khron]

Do you have a DMM? Did you measure the AC voltage at the socket with all the equipment turned on?

The Brymen BM869 should give you microvolts sensitivity. Not expensive.

I can't speak for the OP, but i myself am getting a bit confused - are we now talking about measuring the 100Hz (and harmonics) on the audio output(s) of the device in question?

Or the noise present (or not) on the 50Hz mains?

Or both? Or....?

 

[Cqwet Dbdfte]

I can't speak for the OP, but i myself am getting a bit confused - are we now talking about measuring the 100Hz (and harmonics) on the audio output(s) of the device in question?

Or the noise present (or not) on the 50Hz mains?

Or both? Or....?

No, the 100Hz noise is in the signal, at low levels I expect, but higher than the normal noise of the unit.
An isolated high impedance load on the circuit would not cause an overload nor induce another ground loop.
Remote troubleshooting is difficult as the observer may not catch relevant stuff.
A low pass filter could be added to enhance DMM values.

 

[scott2000]

Not sure I understand the question?

You answered it fine

The issue is only present in the WA

Some things are just built differently.... Divas
Always nice to know you have less than perfect something or other though so not a bad thing if it reveals that...

 

[Matt Syson]

You should start off by buying yourself a multimeter (around 18 Euros at Screwfix or other building supplies place or even some supermarkets) and measure the mains at your power sockets. There will be you tube videos to show how to do this I have no doubt.
You could even buy a mains power meter (I got one at Leroy Merlin or was it ELeclerc Brico as I am in France?). These are effectively a mains plug on one face with a matching socket on the other and it has a display of mains Voltage, Current and Power and is simply plug in so no expertise needed and handy for measuring stuff around the house or studio so you can see where your money goes.
As you say you are rural and have farms nearby I would suspect low mains and although the WA unit SHOULD handle 10 percent low mains you could actually be a bit lower than that (or the WA unit doesn't really conform to specification). you souwed the 100 Hz 'peak but you must have plugged it into something else to get that display since it is neither the WA or headphones.

 

[ruffrecords]

OK, can you do this test. Turn the mic gain down as low as it will go without engaging the the line input. Turn the level control to12 0'clock. Make up a male XLR cable plug with pins 2 and 3 shorted together and plug it into the mic input. Measure the level of hum at the output.

Cheers

Ian

 

[Evertide]

Test as Ian suggested AND turn out the light...

 

[DaveDC]

Hi GLM:

Here is a little tech background that may help you understand how we are analyzing your situation.

Unwanted interference can enter your system from the outside in three ways:

1. Magnetically, like a vibrating electric guitar string near its pickup. Magnetic interference is sensitive to the orientation of the magnetic field, which is why checking the orientation of the device was suggested. Fixing it can be done by reorienting either the sender or the receiver, reducing the strength of the sender’s field, or reducing the sensitivity of the receiver to such fields.

2. Electrostatically, like when you pick up a static charge from petting a cat, then you get zapped when you touch a grounded metal object. Electrostatic coupling is not orientation sensitive, but is sensitive to distance. It is usually fixed by shielding, i.e. interposing a grounded metal surface between the sender and the receiver.

3. Conducted, from a current flowing through a wire that is unintentionally part of your signal path. These are difficult to find in a studio because everything is wired to everything else and current flows every which way. To find this, you need to break all of the wiring except the minimum needed to make the gear run. That is why folks wanted you to use headphones for testing, since they aren’t wired to any other gear. The shorting plug Ian suggested is similarly not connected to other gear.

Unwanted interference can also be generated spontaneously within a piece of gear. Interference can be a byproduct of a mains undervoltage condition, where the unit’s power supply is being starved of voltage. That is why we want you to see if you can measure your mains voltage. A fix might to use a mains transformer to slightly boost the voltage for this particular bit of kit. Or your power utility could choose a different transformer tap for your feed.

I hope this helps.

 

[GLM]

Hi GLM:

Here is a little tech background that may help you understand how we are analyzing your situation.

Unwanted interference can enter your system from the outside in three ways:

1. Magnetically, like a vibrating electric guitar string near its pickup. Magnetic interference is sensitive to the orientation of the magnetic field, which is why checking the orientation of the device was suggested. Fixing it can be done by reorienting either the sender or the receiver, reducing the strength of the sender’s field, or reducing the sensitivity of the receiver to such fields.

2. Electrostatically, like when you pick up a static charge from petting a cat, then you get zapped when you touch a grounded metal object. Electrostatic coupling is not orientation sensitive, but is sensitive to distance. It is usually fixed by shielding, i.e. interposing a grounded metal surface between the sender and the receiver.

3. Conducted, from a current flowing through a wire that is unintentionally part of your signal path. These are difficult to find in a studio because everything is wired to everything else and current flows every which way. To find this, you need to break all of the wiring except the minimum needed to make the gear run. That is why folks wanted you to use headphones for testing, since they aren’t wired to any other gear. The shorting plug Ian suggested is similarly not connected to other gear.

Unwanted interference can also be generated spontaneously within a piece of gear. Interference can be a byproduct of a mains undervoltage condition, where the unit’s power supply is being starved of voltage. That is why we want you to see if you can measure your mains voltage. A fix might to use a mains transformer to slightly boost the voltage for this particular bit of kit. Or your power utility could choose a different transformer tap for your feed.

I hope this helps.

This is incredibly helpful and really generous of you to share your wisdom in a way that I can actually understand.

 

[kidb]

Just to check off more variables, is the power cable 3 pin to the wall? and is the power at your place grounded or 2 prong? Loads of issues with 2 prong arrangements, I’d also suggest removing it from the rack, isolating it from all other metal, to see if that changes anything if not already done, but boy 100hz sure makes me wonder about the switch mode psu in that thing, not sure what else can cause 100hz and not 50hz. Cheers!

 

[NoisyIndividual]

Here's a thing you can try.
Take the mains lead out of the unit and measure resistance between Neutral and Earth on the mains inlet of the equipment.

There shouldn't be anything, it should be open circuit, infinity ohms.
If there is, this can induce hum through your entire system.

The Neutral is usually connected to earth where it enters the building, though in rural Ireland this might actually be anywhere on the planet.

But if you connect Earth to Neutral locally by accident, you could create a massive Earth Loop that will confuse you til you die.


The Isolation transformer you mentioned should actually make a difference if this is the case, either fitted to the offending unit or the whole system.

Edit: In fact given your circumstances I think I would get one for the studio anyway.


It could also be that your "Earth" connection is a pole hammered into the ground outside your house.
Sometimes watering it can help so I've heard, if it isn't boggy enough already.

 

[Cqwet Dbdfte]

A 100Hz noise would exclude magnetically induced noise and point to a low AC mains voltage, as 100Hz and higher harmonics are produced by the rectification.
Divide and conquer, test each piece separately. The WA unit may draw more power sucking down the voltage.
Measure it.

 

[gordon]

Have you measured the Mains Voltage in your area as it sounds rural. Lower mains voltage can result in the Power supply voltage regulator not being able to do its job as it needs enough voltage above the DC rails to be able to regulate.

 

[ccaudle]

Take the mains lead out of the unit and measure resistance between Neutral and Earth.

I feel like people are posting without reading the discussion so far.

First, o.p. had already stated he does not currently have a multi-meter.

Second, the o.p. has already stated he is not experienced or comfortable working on mains power, so providing step by step safety guidelines would be prudent.
The first step would be to point out how to determine which is line and which is neutral in a standard power cord.
The next step would be to verify that there is no voltage between neutral and protective earth. Suggesting to measure resistance without verifying that the system was not miswired is placing too much faith in old rural properties. If it is miswired with hot connected to what should be neutral then blowing the fuse in the meter is the absolute best case. Worst case would be the inexperienced person is lulled into false security assuming the neutral line has no power and suffers shock or electrocution from lack of sufficient safety precautions.

 

[NoisyIndividual]

I did not mean to measure resistance on the house power supply cables, I meant in the equipment that is giving the problem. I have edited my post to make this clear.
If there IS any such connection between Earth and Neutral IN THE EQUIPMENT, it is likely to give all sorts of issues, at least here in the UK and Ireland.

 

[GLM]

Rest assured everyone, that nothing scares me more than electricity! So, nothing will be done with any potential to cause myself some harm.

Fascinating reading the information all the same.

I do have a friend who is a full time electrician. He doesnt understand audio, but he lives and breathes power. So having these suggestions will be really helpful when he (eventually) pays me a visit.