What is this problem?! A phantom power issue?

teainthesahara

teainthesahara

New member
This is ticking me off! One of my pre's is doing something weird.
With a condenser mic hooked up, and phantom power turned on, the signal i am hearing is hissy (big noise floor), 'thin' sounding, and the clip light on the preamp is on constantly. When I hook up a dynamic to the same preamp (phantom off), it sounds and works absolutely fine.

Any ideas?
 
Sounds simple (not to offend) but, have you tried a different condensor mic? Have you tried another cable just to make sure. Those would be the first and most simple things to check. After that we need to know a little more about the phantom source, the mic pre's...are they all integrated into a single mixer board?

Anyone else?
 
Yup, those were the first things I tried, and i was able to rule out the mic's, and the cable as the source of the problem. The mic pre is a stand-alone unit, with a push button switch to turn the phantom power on/off. It's my symtetrix 528 :( . Damn! I was getting such a great sound from this unit (and still am, with the dynamic mics). The schematic for this pre is posted here:

http://www.symetrixaudio.com/tech_support/web_support_only/528.htm

Any more ideas?

Thanks
 
If you have a multimeter check the voltage across pin 1 and 2. as well as 1 and 3

1 neg
2 Pos
3 pos

Should read around 48 volts dc current. on 1 and 2
and 48 volts between 1 and 3
If not, you need to have unit serviced. Could be something as simple as a bad switch.

C
 
Last edited:
Big Kenny: It was an AKG 535eb. It works fine on all my other preamps.


CGibson: Damn! I hoped it was something I could do myself. To check the phantom voltage, you just clip the multimeters leads to the pins on the XLR jack, correct? I was thinking if the labour charge involved in this is going to be expensive, i just might use the thing for dynamic mics for now, and in the future contact these people (http://www.audioupgrades.com/pl1.html) to upgrade the entire unit and fix it at the same time.
 
teainthesahara said:
Big Kenny: It was an AKG 535eb. It works fine on all my other preamps.


CGibson: Damn! I hoped it was something I could do myself. To check the phantom voltage, you just clip the multimeters leads to the pins on the XLR jack, correct? I was thinking if the labour charge involved in this is going to be expensive, i just might use the thing for dynamic mics for now, and in the future contact these people (http://www.audioupgrades.com/pl1.html) to upgrade the entire unit and fix it at the same time.
Click to expand...

You can buy a multimeter for about $20.00
set the dial to DC voltage above 50 volts DC
touch the black lead to the #1 pin
touch the Red lead to #2
you should get a reading between 45 - 50 volts
do the same thing on the #3 pin

Every studio should have one for a number of reasons so the $20.00 investment will go on forever.

C
 
Usually a phantom power problem is going to show itself as really low gain with possibly some distortion. Maybe that mic and pre just don't sound very good together.
 
CGibson - thanks for the instructions. I'll try that today.

TexRoadkill - the description you wrote fits as well; the signal does have very low gain (although the clip light is on). Im quite convinced that it's not a bad mic-preamp match-up; the sound is way to hissy and off in gain i think...i'll try it with a few more condensors just encase though...
 
teainthesahara said:
CGibson - thanks for the instructions. I'll try that today.

TexRoadkill - the description you wrote fits as well; the signal does have very low gain (although the clip light is on). Im quite convinced that it's not a bad mic-preamp match-up; the sound is way to hissy and off in gain i think...i'll try it with a few more condensors just encase though...
Click to expand...


Good Luck Man!
I hate problems like this. Just when everything's going great, poof a flat tire.

C
 
Checking the voltage is a great idea...I'm just wondering if maybe the voltage is falling down under load...this might be a little more difficult to check. The mic needs to be connected. You'll have to carefully...very carefully take the shell off the cable then do the same voltage checks.


sjl
 
punkin said:
Checking the voltage is a great idea...I'm just wondering if maybe the voltage is falling down under load...this might be a little more difficult to check. The mic needs to be connected. You'll have to carefully...very carefully take the shell off the cable then do the same voltage checks.


sjl
Click to expand...

True, very true.
That's also a great idea to check the voltage drop.
It might drop as much as 10 volts with a load but maintain a constant voltage above 35 volts or so.
Good call Punkin

Like punkin said, slide the shell out of the way to expose the back side of the leads before you plug it in.
Check the voltage across the pins but DO NOT cross pins with multimeter leads.

C
 
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