DI & Phantom power question

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LemonTree

LemonTree

Suck 'em and see!
here's a quick rundown of my setup...

Allen & Heath GS1 24/8/2 into my Delta 1010 into my PC

I'm trying to record a bass guitar part over a drum pattern. I can't get enough signal plugging the bass straigh into the line in on the desk, so I've aquired a DI box (CAi Countryman Associates inc). when I take the line out of the DI into the XLR on the desk the signal is still as weak as the line in method.

I've switched the Phantom power on and the signal is greatly boosted but, there's a horrible BUZZ comming through my monitors. I've tried switching the ground on the DI box.

Any ideas what could be causing this? Is it normal to get a line buzz when using Phantom power?
 
Ahh, you probably have a bass with single coils, try turning your pc monitor off, the buzz may dissappear.....


Amund
 
Damn Lemon Tree,

Do you have ANY idea what Phantom Power is???
Well, lemme tell ya: It ain't for boosting signals!
it is used to power up cond. mics!

.. and do you have ANY idea what a DI is used for??
it's to get high-Z signals into Low-z balanced signals to run over longer distances.

The DI is always a good idea to plug your bass. It will get a cleaner signal to your desk, some DI's have a groundlift which is handy.

What you need is a plain'ol amplifier.

please be gentle with the Phantom Power next time, it has the power to destroy some precious mics if you don't care.
(and ALWAYS use balanced lines, you know them XLR things...!!)

you're a lucky boy if ya didn't destroy something already.

my advise is to get to know the things you have and want to use, so you will have happier times and get great recordings.
I know you will!

good luck with it
 
roman said:
Damn Lemon Tree,

Do you have ANY idea what Phantom Power is???
Well, lemme tell ya: It ain't for boosting signals!
it is used to power up cond. mics!

.. and do you have ANY idea what a DI is used for??
it's to get high-Z signals into Low-z balanced signals to run over longer distances. ...<snip>...
Click to expand...
Unless the phantom is powering the DI, in which case that's exactly what he should be doing. It could be a pasive (I don't know) but it still should not be a problem.

The DI is getting the bass to the board's mic pre so at least you're on the right track LT.
Wayne
 
passive

Type 85 Direct Box Specifications
Input Resistance :
Pickup mode:10,000,000 ohms, 10 times the input resistance of a typical guitar amplifier

Speaker mode: 10k ohms


Input Capacitance :

60 Picofarads, equal to two feet of low capacitance guitar cable.


Maximum Input Level :

Pickup mode: 5 Volts P-P

Speaker mode: 300 Volts P-P
Equal to 2,800 watts into 4 ohms.


Input Protection :

220 Volts RMS and 20,000 Volt static discharges.


Voltage Gain :

Pickup mode: -10dB
Speaker mode: -46 dB


Noise (shorted input) :

149 dB SPL, 1 kHz at 1% T.H.D.


Frequency Response :

20Hz to 20kHz ± 1dB


Distortion :

0.018% THD @ 1kHz and 1 V P-P in
0.08% IMD 10kHz/60Hz 1 V P-P in


R.F. Filtering :

250 kHz Low Pass on input
30kHz Low Pass on output


Power Requirements :

48 V @ 0.4 ma Phantom or 9 V battery


Dimensions :

1.75 in. x 3 in. x 5 in.
(45 mm) x (77 mm) x (127 mm)


Weight :

18.5 oz. (0.52 kg)




But I'm still getting that low level hum/buzz when the trim goes up to about ¾ on the board.

Is phantom power generaly noisy? I'm actualy still getting the buzz with NOTHING plugged into the board at all
 
Last edited:
Re: passive

LemonTree said:
...<snip>...
Power Requirements :

48 V @ 0.4 ma Phantom or 9 V battery

But I'm still getting that low level hum/buzz when the trim goes up to about ¾ on the board.

Is phantom power generaly noisy? I'm actualy still getting the buzz with NOTHING plugged into the board at all
Click to expand...

Phantom power on, (or battery -not both), there should be no added noise (unless you have the pre-gain way up, then maybe some).
But you're getting the noise with nothing plugged in? Is the phantom being on making a diference here or not?
Wayne
 
yeah the phantom being on brings in the buzz, and there's no battery in the DI box. But I've got the trims up so far to hear it now I don't really think it's an issue any more. I's much worse through the headphones than it is through the monitors. To hear it throught the monitors I need to turn the monitor level up to about 9.....this is with nothing plugged into any of the channels and all the faders on the ground floor.

Just the age of the desk I guess and I can't hear it on the recording when I play it back so £200 well spent I think
 
No... the 'phantom thing' isn't bringing in the buzz... the 'phantom thing' is allowing the active amplifier in the Countryman to work.

Phantom power is used to power amplifiers. There is an amplifier that requires power to operate in a FET condenser microphone, there is an amplifier in the Countryman Associates DI... that's why it's called an "active DI". A "passive DI" employs a transformer to alter the impedance from around 10k ohms to like 1k, an active DI does this via an internal amplifier [+/- 3db].

The 'buzz' you are experiencing could be caused by any one of a myriad of problems. It could be 'airbourne' as 'Plexi' suggested, it could be a 'ground loop'.

If it's 'airbourne', it should be reduced by shutting off the computer monitor, or moving farther away from the computer monitor... it should also be reduced when you touch the strings.

If it's a ground loop... you might try using a battery in your DI box and adding a 'pin 1 lift' adapter between the output of the DI and the input of your desk. This will 'lift' the audio ground from the DI to the desk... but will also kill the supply of phantom power to the unit as phantom power uses 'pin 1' for it's '0 volt reference' (ground)... if you kill the phantom power, the amplifier won't work unless you a battery installed in the unit.

Best of luck sorting out your problem...
 
Here's a goofy trick that I used before to get rid of bass hum.

Plug bass into D.I.

Plug D.I. into mixer.

Have Bass Player remove 1 shoe and sock.

Place bare foot of Bass player on metal surface (oooh cold!) of D.I.

Viola!

I don't know exactly why this worked, but it did.

Love to hear why, and I'm sure I will:D
 
ground loops can be dangerous.

you create the possibility of injuring, perhaps even killing a person, by allowing ground loops to continue... and especially if your method of "fixing" it involves using the person as a ground lead. if there was a short/electrical problem, and the current was sent down the common ground line (generally pin 1 on balanced cables is connected to the electrical ground socket as well as metal surfaces, correct me if i'm wrong), your bass player could get all of that current going through him.

i had a talk with a live sound guy who was working a show in which a high-power tube guitar amp had its ground wire severed (i now refuse to work with people who have one), and the guitarist was sent to ER because of the shock when his lips touched the vocal mic.

make no mistake, sound jobs really are a life-and-death business :)
 
Yes, I narrowly escaped getting seriously zapped myself, same exact situation, but my guitar took the brunt of it, melted the string instantly & left a nice little burn mark on the headstock where the string touched the mic!

In the first post above, I was using no amp, no phantom power, so there wasn't enough current to hurt anyone.

This is definately not a first course of action, and won't work for all situations. But the noise disappeared whenever I would pick up the D.I., so I just had the bass player step on it the whole time and it worked!

PROCEED WITH CAUTION

I sure don't want anyone to get hurt!
 
Only if you are using your blow-dryer also, and smoking while you put hair-spray on your head.
 
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