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[Tommy Peel]

The normal sound person at church asked me to come by after work today to look at their assisted listening system because it has a terrible sounding scratchy hum coming from the receivers. The system is a Nady ALD-800( http://www.nady.com/ald800.html ) which I realize is most likely the problem. When the transmitter is off the receivers have a relatively small amount of background noise. When the transmitter is switched on and unplugged from the mixer(x32 if it matters) there is the aforementioned scratchy hum(possibly AC hum but I'm not 100% sure). The noise varies when you move the receiver around but is always fairly loud. If a CD is played the noise fades into the music somewhat and is much less noticeable but when someone is speaking through a mic the noise comes close to drowning out the speaker. I've tried increasing the output level on the mixer and on the transmitter with no luck. The church does have 2 Sennheiser wireless handheld mics(and will be getting 4 more when Musicians Friend gets some more because they back ordered them) and a Shure wireless lapel mic. However whether these were on or off made no difference. Changing the plug and circuit it was plugged into made no difference. Whether the receiver was 1 foot or 100 from the transmitter made little difference.

Questions: Is there any way to tweak the current system to make it better? If not, what is a good system/brand of system to get?


Thanks,
Tommy


Sent from my iPad using Tapatalk HD

[brian maddox]

well here's my thoughts.

sounds like the Automatic Level Control is bringing up the level of noise that is being introduced at the input.

the unit has a mic and a line input.  coming from an X32, it should be plugged into the line input.  the mic input has voltage on it for an electret mic and would probably cause this issue if it's being used.

if the line input is being used, the input level control may be too high.

or, the adapter you are using to get the XLR to the 1/4" input may be wrong.  it should be a proper XLR to T-S unbalanced adapter, or perhaps a balanced to unbalanced transformer.

in short, assuming the unit isn't just broken, something is causing the noise at teh input and then the ALC is raising that level in the absence of input signal to the loud level you're hearing.  figure out what is causing the noise at the input, and you'll find the problem.

i think. 

[David Kaiser]

How old is the ALD-800 transmitter? That Nady hearing assistance system has been around for a long time. It may simply need some TLC from the Manufacturer. I have two Williams Sound Transmitters from the 90's that both went on the fritz over Thanksgiving weekend.  The one for hearing assistance suddenly wouldn't transmit more than 20 feet and the one for the Spanish translation developed a huge hum that only went mostly away when a heavy case was placed on the top of the transmitter. Both had been working excellently at the previous conference.

[Jerome Malsack]

With the wall wart power supply's you will find that moving the power supplies and other gear near the transmitter might correct or change the problem. 

I have the Carvin PM-100  basically same as your Nady.

Possible also a ground lift issue on the power supply. 
Try running a DI with ground lift and see if this helps on the hum.  The plugs on the wall wart allow reversing the plug.  Try turning 180 degrees in outlet.   

[Tommy Peel]

How old is the ALD-800 transmitter? That Nady hearing assistance system has been around for a long time. It may simply need some TLC from the Manufacturer. I have two Williams Sound Transmitters from the 90's that both went on the fritz over Thanksgiving weekend.  The one for hearing assistance suddenly wouldn't transmit more than 20 feet and the one for the Spanish translation developed a huge hum that only went mostly away when a heavy case was placed on the top of the transmitter. Both had been working excellently at the previous conference.

The system isn't very old; maybe 3-5 years old. I remember them getting it to replace the old system they used to use.

With the wall wart power supply's you will find that moving the power supplies and other gear near the transmitter might correct or change the problem. 

I have the Carvin PM-100  basically same as your Nady.

Possible also a ground lift issue on the power supply. 
Try running a DI with ground lift and see if this helps on the hum.  The plugs on the wall wart allow reversing the plug.  Try turning 180 degrees in outlet.   

I tried the wall wart flipped both ways. The transmitter was originally setup behind the stage on top of the power amps. Before I made this post I moved it to FOH near the sound board in an attempt to help but it made no difference. I'll try the DI ground lift next time I get a chance but being that it does it unplugged I doubt it'll matter. The normal sound guy ended up moving to the floor in the sound booth(which is one of those terrible ones located in a loft like space above  the foyer maybe 10 feet from the ground floor to the floor of the sound booth) and lowering the antenna. Anyway he said it was better. I'll look at it tonight when I go up there to install a couple of new wireless mics and see how it is now.

Do you know of a better system to buy if we were to replace it?

Thanks,
Tommy

[Jerome Malsack]

You could look into www.assistedaudio.com 

Williams Sound PPA377   

Replacing the transmitter with a better quality would mean your receivers would still work.  One of these receivers should not have a ground loop issue. 

Stationare Transmitter  LT-800-072   around  $500.00

[Brad Weber]

Replacing the transmitter with a better quality would mean your receivers would still work.

Did you verify that for that transmitter with the specific exiting receivers as not all manufacturers and models use exactly the same tunings within the 72MHz ALS band?
 
You mentioned that the Nady system is 3-5 years old and replaced an earlier system.  Has the Nady system ever worked properly?  If so, did anything change around the time this problem started?
 
Have you verified the mix and levels going to the ALS transmitter?  The fact that CD playback 'pushes' the noise down while a mic signal doesn't suggests it may be a mix or gain structure issue.
 
Another possible option is that over time and with all the moving the transmitter frequency may have drifted a bit.  Then there is the off chance that someone opened up the transmitter and changed the internal dip switch settings.
 
And the obvious one, has anyone talked to Nady?

[Bob L. Wilson]

Did you verify that for that transmitter with the specific exiting receivers as not all manufacturers and models use exactly the same tunings within the 72MHz ALS band?
 
You mentioned that the Nady system is 3-5 years old and replaced an earlier system.  Has the Nady system ever worked properly?  If so, did anything change around the time this problem started?
 
Have you verified the mix and levels going to the ALS transmitter?  The fact that CD playback 'pushes' the noise down while a mic signal doesn't suggests it may be a mix or gain structure issue.
 
Another possible option is that over time and with all the moving the transmitter frequency may have drifted a bit.  Then there is the off chance that someone opened up the transmitter and changed the internal dip switch settings.
 
And the obvious one, has anyone talked to Nady?

Slightly less obvious but probably just as likely, knowing how Nady gear is built, when you have the transmitter open to check the dip switch settings look for leaking bulging capacitors. Defective cheap caps from that era are killing all kinds of gear long before its time. Just google "bad capacitors" or check out this link http://www.badcaps.net/ for lots of pictures of what to look for.

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