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Noise from Phantom Power (Neumann/Avalon)
Old 16th May 2003
Gear Maniac
oortnyc's Avatar

Noise from Phantom Power (Neumann/Avalon)

When I plug my Neumann TLM-103 inot my Avalon 737SP I get a very bad sizzle noise on the mic. I tracked it down to the phantom power of the avalon. If I send phantom to the TLM from another source (Brent Neve, MackieD8B) the mic works fine and the avalon sounds great. I tried the avalon with a 414 and it works fine. Avalon said that it is a problem with the mic not being able to handle true 48v phantom, they have seen this problem with other mics but never Neumann. Is my TLM in need of service? If so, where should I send it? Why does it work fine with other phantom sources? Any Thoughts?
Old 17th May 2003
Lives for gear

If you have a multimeter you could take a look at the phantom coming from each unit and see which run on what voltages to give you an idea if the "48 Volt" theory makes sense. It is unlikely a Neumann couldn't handle 48 Volts - this has been the nominal phantom power voltage since Mozart was a kid.
Old 17th May 2003
Lives for gear
C.Lambrechts's Avatar

on the other hand the avalon seems to work fine with other mics ... which for me puts the TLM in as suspect number one. The TLM series isn't exactly Neumann's 'finest' range imho but that shouldn't have anything to do with it.

Best thing to do would be to try the TLM with another 737sp unit and see if it acts the same. Where are you based ... maybe another GS in your neighbourhood with a 737 ???
Old 17th May 2003
Gear Maniac
oortnyc's Avatar

my Brent Neve is puttng out 48.3Vdc and the 737 is at 51.2Vdc. But I don't think this really shouldn't matter. Doesn't the mic actually attenuate the voltage down to about 35Vdc. Not really sure. To me it seems like something faulty in the mic. Do I have to send it to Neumann or is there someone in NYC that reapirs these?
Old 17th May 2003
BevvyB's Avatar

no probs here with exactly that config
Old 17th May 2003
Gear Maniac
oortnyc's Avatar

If you don't mind checking, what voltage is the 737 putting out? Thanks
Old 19th May 2003
Tim Farrant's Avatar

I seem to recall another post somewhere of this exact same problem. You have to remember that generally the 48V is fed onto the mic lines via 2x 6k8 resistors (not sure if this is the case with the Avalon - sound like it is not) So the actual voltage arriving at the mic will depend upon the amount of current it is drawing. This is why the voltage is so high in the first place. A mic that draws alot of power, such as the TLM170 at 10mA I believe, brings the actaul voltage arriving at the mic down to about 20V (when fed via 2x 6k8 ohms).

Therefore, you need to measure the voltage with a mic connected. If the 48V is applied to the mic line via a centre tap on the input transformer with no feed in resistor (like the old days), the voltage arriving at the mic will be 48V, which may upset some microphones.

Gee - I hope this makes sense...

Old 19th May 2003
Lives for gear
doug_hti's Avatar

sounds like the mic, hope you get it worked out.

However, in the mean time. Have you really made sure you don't have any interference, such as lights, dimmers, electrical stuff, etc. around. I have a 737, and I get a buzzing, a bit higher than a 60 hz special, that only comes in when I have the EQ inserted, at certain times. Found out it was a dimmer in another room.
Old 19th May 2003
Gear Maniac
oortnyc's Avatar

The 737 works fine with a 414 and with a tube mic that has its own power supply so I am pretty sure that it is the mic. I have been working around it by multing the mic and getting phantom from another pre. But I would like to know if the mic needs repair. If this is a problem then there may be other problems with the mics sound. I do not have another TLM103 to compare it to. - Does anythone know a place in NYC to fix Neumann's? Thanks
Old 19th May 2003
Lives for gear

My guess is the phantom regulator in the Avalon has gone south.

When it's noisy, the unbalanced audio output of the TLM-103 converts this noise from common mode to a differential signal. This is what you're hearing.

This'll happen with some of the AT mics too.

A mic with a truly balanced output will ignore the noise to a much greater degreee and you won't hear it.

The fact that you can power the mic from another source and have it quiet with the Avalon tends to support this too.
Old 21st May 2003
Gear Maniac
oortnyc's Avatar

I appreciate all of the input!!!
I did some phantom testing:
Brent/Neve w/ No load = 49.2VDC
Avalon 737 w/ no load = 51.3VDC

Brent w/ TLM103 = 38.7VDC
Avalon w/ TLM103 = 38.9VDC

Brent w/ 414 = 42VDC
Avalon w/ 414 = 42.5VDC

So they are basically the same readings. I found out that like Dan said I get the same problems from my Avalon with a AT4030. So is the problem with the Avalon or just the combination of the Avalon with certain mics?

Thanks -

Starting to look like I have to box up the Avalon.
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