Phantom Noise

[sonolink]

I'm finishing an 8 channels Eden preamp unit made out of Rochey's Eden preamps, MicFE and control boards. The thing is that one problem I have found on this build is that when Phantom is engaged there is a slight crackling/windy noise in the background. A solution that was offered to me was to implement a Low Pass RC filter.

A few weeks ago I bought  a 4x 312 APIs with Fabio boards from a member of this forum. The unit is well built and sounds great with dynamic mics. When testing it with a condenser what was my surprise to hear the same slight crackling/windy noise in the background!!

So I asked myself:

-is it the mic? (a Behringer cheap calibration mic)
-is it a lack of RC Filter in the API unit too?
-what is the root of this problem?

I will test both units with a good condenser mic as soon as I bring opne from the studio but I don't think it is the  mic...

Any ideas?
Thanks
Sono

 

[emrr]

I would bet on the mic.  If I recall one of the B cal mics has a highly non-symmetrical current draw. 

 

[[silent:arts]]

One Mic and 12 Channels (two different circuits / design) with this problem?
I would try another Mic.

 

[JohnRoberts]

I'm finishing an 8 channels Eden preamp unit made out of Rochey's Eden preamps, MicFE and control boards. The thing is that one problem I have found on this build is that when Phantom is engaged there is a slight crackling/windy noise in the background. A solution that was offered to me was to implement a Low Pass RC filter.

A few weeks ago I bought  a 4x 312 APIs with Fabio boards from a member of this forum. The unit is well built and sounds great with dynamic mics. When testing it with a condenser what was my surprise to hear the same slight crackling/windy noise in the background!!

So I asked myself:

-is it the mic? (a Behringer cheap calibration mic)
-is it a lack of RC Filter in the API unit too?
-what is the root of this problem?

I will test both units with a good condenser mic as soon as I bring opne from the studio but I don't think it is the  mic...

Any ideas?
Thanks
Sono

The noise could come from different things.

Are all 4 exactly the same?

While dynamic mics will generally ignore phantom voltage, you can us a 200 ohm resistor in place of a mic, and see if you hear that noise with phantom engaged. 

This is still not definitive since  phantom mics draw current that will change input conditions.

You can mimic this too with two more resistors from pins 2 and 3 connected to pin 1 (say 10K 1%).

If the preamps are still dead silent you may have an issue with the mic's active circuitry, Another possible obscure fault is wiring /connection error that imbalances the input, preventing some common mode noise from cancelling out.

Not a single obvious candidate but several possibilities you should check.

JR 

PS Isn't a cheap Behringer mic redundant?  :

 

[sonolink]

[quote author=JohnRoberts]
PS Isn't a cheap Behringer mic redundant?  :
[/quote]

It is actually......but as usual it's a long story......I have moved to live near the studio so right now the house is a cardboard boxes mess and I wanted to finish both preamps (the 312s needed to be changed from 120 to 240VAC) and then I saw this blackbox in the middle of all my things and remembered it's that Behringer calibration mic I bought about 10 years ago after downloading Room EQ Wizard to check if my recently built mixing room freq response was ok........and never used cos my partner had a really cool Bruel&Kjaer Soundmeter!!
So anyway when I saw the black box I thought Hey it's a condenser, right? I can test for phantom....

I will check with a proper mic and will try JohnRoberts suggestions
Thanks to all for the input!

 

[Gene Pink]

Small diaphragm condenser mics that get some moisture in them can exhibit a sort of "popcorn", or frying bacon noise at a low level. Probably due to internal dust. My condensers, used outside on a show on a really humid day, will do that now and then.

We simply gate them and ignore it, as these condensers are usually on a drum kit hi-hat and L-R overheads anyway, where gating would be appropriate anyway.

Gene

 

[sonolink]

Small diaphragm condenser mics that get some moisture in them can exhibit a sort of "popcorn", or frying bacon noise at a low level.
We simply gate them and ignore it, as these condensers are usually on a drum kit hi-hat and L-R overheads anyway, where gating would be appropriate anyway.

Don't get me wrong, I get your point and appreciate your input but  my point was to determine the source/root of the problem

Personally I seldom use mics over HH (451 kinda thing I understand) since I find that with OHs well placed it's enough and I never really use gates on OHs since generally I always "hear" them on tails etc...

In any case, I find that gates or no gates, the noise is still there. You might not hear it upfront when the music is on but it's there and affects the sound. Keep in mind that this is in a studio context... So the solution is to find out where the noise comes from to get RID of it. Also I tend to avoid keeping crap down since crap always tends to float and spill you right in the face especially after compressing, mixing and mastering!

Thanks for the moisture tip though. I hadn't thought of that.

Cheers
Sono

 

[sonolink]

Ok so it wasn't any of the above. I forgot to mention that the preamps line outs were connected to a Behringer ADA8000 connected to a MOTU 896mk3 line input.

I tried the calibration mic on a mic input directly on the MOTU and it was silent as gold.....so I connected the line output of the 312s to a MOTU input and HEY no noise!! So obviously thre ADA8000 was creating the noise....
The Edens are not TOTALLY silent but s/n ratio is excellent!

Anyway problem source found and sorted
Thanks a lot for the input guys!!
Cheers
Sono

 

[JohnRoberts]

Ok so it wasn't any of the above. I forgot to mention that the preamps line outs were connected to a Behringer ADA8000 connected to a MOTU 896mk3 line input.

I tried the calibration mic on a mic input directly on the MOTU and it was silent as gold.....so I connected the line output of the 312s to a MOTU input and HEY no noise!! So obviously thre ADA8000 was creating the noise....
The Edens are not TOTALLY silent but s/n ratio is excellent!

Anyway problem source found and sorted
Thanks a lot for the input guys!!
Cheers
Sono

So why was the noise not present for dynamic mics?

JR 

 

[sonolink]

Good question......  ???

Gotta do the resistors thing then....

 

[ricardo]

So why was the noise not present for dynamic mics?

I can well believe that the Behringer ADA8000 sprays enough yucky RFI to affect the electronics in the Behringer mike.  (This type of 'RFI' noise is due to demodulation

It can come through the leads and/or the shields and affect mikes with poor CMR.  I think Dorsey & Royer have posted articles on how to improve CMR on cheapo mikes including (some versions) of the Behringer measurement mike.

P48V supplies themselves can be noisy and again this is affected by poor CMR of mikes.  See eg

http://www.audiomastersforum.net/amforum/index.php/topic,8654.msg77163.html#msg77163
http://outrecording.com/tascam-dr-680-noise-test/ http://outrecording.com/tascam-dr-680-noise-test/

.. but poor P48V is not the problem in this case.

A dynamic mike floating at LoZ and without active bits won't react to RFI which will be determined by the preamp, its CMR, its earthing arrangements bla bla ...

 

[sonolink]

Hello everybody

I'm back with the same problem. I have tried several mics and 3 mic preamps but I always hear that kinda of light frying pan noise in the background when engaging phantom. When I use dynamic mics there is no noise at all.
I've tested running a Neumann TLM103, an AKG 414 and the same Behringer calibrating mic. I've tried with the API Fabio clone, an 8 channels Eden and a MOTU 896mk3. I've tried several cables. Same thing...

Any chance it could come from my house electrical installation? (The noise is NOT hum)

Thanks for your help

 

[ruffrecords]

Have you put a scope on the phantom supply when it is deeding a condenser mic?  AC couple it and turn the sensitivity right up.

Cheers

Ian

 

[sonolink]

I'm sorry I do have a scope but I don't know how to do what you suggest. What does "deeding" mean btw? Sorry for the language barrier....

 

[ruffrecords]

I'm sorry I do have a scope but I don't know how to do what you suggest. What does "deeding" mean btw? Sorry for the language barrier....

Sorry, my bad typo. I meant feeding a condenser mic; in other words when the phantom power is on and a condenser mic is connected.

Cheers

Ian

 

[RuudNL]

Did you try the test with the two 10 K resistors as mentioned before?

"You can mimic this too with two more resistors from pins 2 and 3 connected to pin 1 (say 10K 1%)."

This proves if the problem is in the microphone or in the microphone amplifier!

 

[sonolink]

Sorry, my bad typo. I meant feeding a condenser mic; in other words when the phantom power is on and a condenser mic is connected.

Oh I see what you mean
So you mean connecting the scope to pin 2 and gnd or pin 3 and gnd?
What do you mean by "AC couple it"? Again sorry for my English

Did you try the test with the two 10 K resistors as mentioned before?
"You can mimic this too with two more resistors from pins 2 and 3 connected to pin 1 (say 10K 1%)."
This proves if the problem is in the microphone or in the microphone amplifier!

No. I didn't since the problem exists with 3 different mics and 3 different preamps.

 

[JohnRoberts]

Sorry, my bad typo. I meant feeding a condenser mic; in other words when the phantom power is on and a condenser mic is connected.

Oh I see what you mean
So you mean connecting the scope to pin 2 and gnd or pin 3 and gnd?
What do you mean by "AC couple it"? Again sorry for my English

Did you try the test with the two 10 K resistors as mentioned before?
"You can mimic this too with two more resistors from pins 2 and 3 connected to pin 1 (say 10K 1%)."
This proves if the problem is in the microphone or in the microphone amplifier!

No. I didn't since the problem exists with 3 different mics and 3 different preamps.

You need to rule out possibilities using deductive reasoning, what remains is your noise source.

If you can rule out the preamps, what remains are the mics.

Perhaps another experiment is to intentionally imbalance the input (with different value resistors  say 10k and 11k, don't need to be 1%. if that causes noise, it is coming from phantom supply  but mic is affecting it's ability to reject the noise. 

In theory a rogue mic cable could affect this ability to reject common mode noise too, but not very likely.

JR

 

[ruffrecords]

Sorry, my bad typo. I meant feeding a condenser mic; in other words when the phantom power is on and a condenser mic is connected.

Oh I see what you mean
So you mean connecting the scope to pin 2 and gnd or pin 3 and gnd?
What do you mean by "AC couple it"? Again sorry for my English

Most scopes have a switch on the input that has three positions, AC, DC or GND. The AC setting switches in a capacitor in series with the input so any dc voltage (in this case the 48V) has no effect. All you see is the AC signal which is what we want to see.

Cheers

Ian

 

[sonolink]

Yes of course. My scope is a cheap digital Owon but it has that. Thanks for clarifying

I'll report back as soon as I've  connected the scope.
Thanks a lot

Cheers
Sono