VO-BB - 20 YEARS OLD!

[Rob Ellis]

Just got a new pre-amp after selling the Avalon. It's a Brent Averill 1073 desktop. LUV it, esp on the 416.

BUT...I'm getting an audible hum from it--not terrible, but it bothers me. And say what you will about the Avalon, I didn't have this problem.

I have isolated what seems like everything. Also recorded into my laptop without the laptop plugged into a wall outlet and still got the hum, so that would seem to eliminate any electrical circuit question. I use a short XLR mic cable or or XLR cable to connect to my interface and it's never been a problem before.

BTW it's not the interface cuz I have two and it happens with both of them.

Also not the 10 ft. mic cables I use to connect the mics to the pre-amp, because when I plug the mics directly into the interface, no hum. But when I do this and just turn on the pre-amp, the hum appears (even though the mics are not plugged into the pre-amp.) So just introducing the pre-amp into the signal chain (again, even though the mics aren't plugged into and phantom power isn't engaged) causes the dreaded hu,m.

Any thoughts you have are most welcome.

This is really frustrating because I love this new pre-amp.

[cyclometh]

Any chance the preamp is picking up hum from an external electrical signal? Does it ever waver or change tone?
_________________
Corey "Vox Man" Snow
http://voxman.net

[JTVG]

I had this problem in my new studio with the power supply for my mic. In fact, I stayed up all night long trying to figure it out. I finally noticed when I moved the PS out of the booth and plugged it into a surge strip, the hum went away. I had previously tried all the outlets in the room using an extension cord to reach them, a different surge strip, going direct into a line conditioner and nothing worked expect going direct into this one particular strip. I have no idea why. Deirdre mentioned on here she uses 3 prong to 2 prong outlet adapters to fix hum. Might be worth trying that.
_________________
Joe Szymanski
http://www.joethevoiceguy.com

[Rob Ellis]

Here's a sound sample spoken slowly so you can hear the hum between words

http://WWW.ROBELLIS.INFO/images/mics_into_Brent_Averill.mp3


Let me know if you hear it, or if you think I'm being too picky. I think I hear it more on the 416.

[cyclometh]

I can definitely hear it. It's a 60hz tone and implies something going on with power for the preamp, since you've isolated everything else. Can you run the preamp on a different circuit? Should also check grounding on the circuit you're using for its power.
_________________
Corey "Vox Man" Snow
http://voxman.net

[cyclometh]

I uploaded a sample test tone at the same frequency here:

http://www.cyclometh.com/audio/60hztone.mp3

It's a bit louder (by design) than the tone on your sample, but you can hear that the pitch is identical. It's a square wave 60hz tone.
_________________
Corey "Vox Man" Snow
http://voxman.net

[Rob Ellis]

I wonder if this would do the trick

http://www.samedaymusic.com/product--EBTHEXLR

[cyclometh]

[cyclometh]

More possibilities to check out (from what I've seen/read, it sounds like the usual culprit is a ground loop or other grounding issue):

http://ask.metafilter.com/171268/Help-me-rid-myself-of-this-annoying-hum
http://www.native-instruments.com/knowledge/questions/269/How+to+get+rid+of+ground+loops+%2850+or+60+hz+hum%29%3F
_________________
Corey "Vox Man" Snow
http://voxman.net

[Mike Sommer]

Check all your connections-- seems like you have. Check them again.

The next thing to do is find out if the hum is from the Brent Averill and not some caprice of the audio chain. It could very easily be a wire shifted in the box and is giving you a power supply hum.

If you have a friend with a studio, take it over there and see if you still get a hum from the box.


If the pre is clean then it could be a ground loop hum. A ground loop lift will help -such as the box you noted in this thread. (There can be problems with these classic pres and modern equipment not wanting to play well together in regards grounding path which leads to hum. )

Also try Quad 4 XLR cables.

The hum sounds pretty low grade, so check and make sure power supplies and AC lines are not crossing or mixing with audi cable. And note where the unit is sitting, the box should reject noise RF or AC interference, but you could be next to a really strong field.

Good luck. Happy hunting.
_________________
The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

[Rob Ellis]

What's interesting is that the sound samples were recorded at 35 db, and then when I amplify (by about 15 db) the hum becomes more prominent.

But when I record at 40 db and then amplify, there is almost not any hum at all.

Maybe I just need to always keep it at 40 db or higher when recording.

I prefer to record a little lower just to keep the room tone down, but it's not clipping or anything at 40 db.

I'm using a 5 ft. Monster cable to run between the pre and interface, which has always seemed to work fine.

[Mike Sommer]

Like I said it's a pretty low grade hum.

So, if I'm following you correctly when you set the Brent Averill at 35 dB
and boost the gain in the DAW you get the hum, but when you set the BA
to 40 dB and boost in the DAW no hum-- Correct?

And I'm assuming by the word "amplify" you mean boosting the signal in
DAW or Normalizing?

So it sounds like the hum is coming "most likely" from the path between the
pre and the interface. Or, form the interface and the computer. It's not
coming from between the the mic and the pre. If it was the hum would be
amplified equally with the the mic signal.


Next: Let me be frank. Monster Cable is crape. There I said it. It's
over priced hype. A Quad 4 XLR cable or Star Quad Audio Cable, helps
provide electromagnetic shielding through a simple process of twisting the
leads together. When you twist two wires together you are in effect
making a capacitor (gimmick capacitor) and this helps shield stray RF and
electromagnetic fields from entering or escaping the leads and thus creating
hum. Or a straight wire is an antenna, capable of transmitting or receiving
a signal- twist two wires together and it is no longer an antenna.

In the image below from our good friends at Canar illustrates how there
are two like colored leads, the blue wires are twisted together and so are
the whites, the breaded shield adds extra protection.



Let's also understand whenever you bring a new pice of gear into the mix
you risk the possibility of hum. This is why big studios spend thousands of
dollars designing, installing and checking their equipment grounding systems.
So your old cable may have been working fine with your other preamp, but
this Discreet Class A solid-state preamp can and will change things like
impedance, which will make noise (that was always there) more noticeable.

Pre-made off the shelf Quad cables are expensive. I get raw Quad cable
off the shelf for about .50¢ a foot; along with some Neutrik connectors and
a little soldering, and you'll have the best cables on the block.

This Bloke makes it look easy, which it is when your shield is twisted and not
braided, and you only have 3 leads to deal with and not 5. (Note the burn
marks on the hands.-- good times)
http://www.youtube.com/watch?v=sRvkd9XBbpc
_________________
The Blog:
http://voiceoveraudio.blogspot.com/

Acoustics are counter-intuitive. If one thing is certain about acoustics, it is that if anything seems obvious it is probably wrong.

[Rob Ellis]

I also tried a Blue mic cable---didn't make any difference.

[Rob Ellis]

Would this be the right stuff?

http://www.fullcompass.com/product/280769.html

[Mike Sommer]