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Help Connecting Mic Preamp To Fireface
Old 28th January 2007
  #1
Here for the gear
 

Help Connecting Mic Preamp To Fireface

I am the proud owner of a FF400.

I would like to connect my SPL GoldMike mic preamp to my FF400. I'm not sure how best to do this! I hope someone can help.

My GoldMike mic preamp has two outputs:

1. balanced XLR +4dBu
2. unbalanced jack 0dBu

My FF400 has these inputs (stolen from manual):

TRS Line Rear (Inputs 5-8)
The Fireface has balanced line inputs as 1/4" TRS jacks on the back of the unit. The electronic input stage is built in a servo balanced design which handles unbalanced (mono jacks) and balanced (stereo jacks) correctly, automatically adjusting the level reference.

When using unbalanced cables with TRS jacks: be sure to connect the 'ring' contact of the TRS jack to ground. Otherwise noise may occur, caused by the unconnected negative input of the balanced input.
One of the main issues when working with an AD-converter is to maintain the full dynamic range within the best operating level. Therefore the Fireface 400 internally uses hi-quality electronic switches, which allow for a perfect adaptation of all rear inputs to the three most often used studio levels.

The 'standardized' studio levels do not result in a (often desired) full scale level, but take some additional digital headroom into consideration. The amount of headroom is different in different standards, and again differently implemented by different manufacturers. Because of this we decided to define the levels of the Fireface in the most compatible way.

Reference 0 dBFS @ Headroom
Lo Gain +19 dBu 15 dB
+4 dBu +13 dBu 9 dB
-10 dBV +2 dBV 12 dB

With +4 dBu selected, the according headroom meets the latest EBU recommendations for Broadcast usage. At -10 dBV a headroom of 12 dB is common practice, each mixing desk operating at -10 dBV is able to send and receive much higher levels. Lo Gain is best suited for professional users who prefer to work balanced and at highest levels. Lo Gain provides 15 dB headroom at +4 dBu nominal level.

Neutrik Combo - Microphone / Line Front (Inputs 1-2)
The balanced microphone inputs of the Fireface 400 offer an adjustable gain of 10 dB up to 65 dB. The soft switching, hi-current Phantom power (48 Volt) provides a professional handling of condensor mics. The usage of a hi-end integrated circuit (PGA 2500) guarantees outstanding sound quality, stunning low THD, and maximum Signal to Noise ratio in any gain setting.

The two combo jacks also allow for the usage of mono and stereo TRS jacks. These jacks usually carry line level signals. To adress this correctly, the input gain can be lowered to 0 dB. The inputs are still operating servo-balanced, but can now handle levels up to +10 dBu.

Overall the inputs 1/2 can work with levels from –55 dBu up to +10 dBu. Two LEDs display a present signal (from –65 dBFS on) and warn against overload (-2 dBFS).

TRS Instrument / Line Front (Inputs 3-4)
The instrument inputs 3/4 of the Fireface 400 are exceptionally flexible. Several gain and impedance options make them the ideal receivers for both line and instrument signals.

Line
Inputs 3/4 have balanced line inputs as 1/4" TRS jacks. The electronic input stage is built in a servo balanced design which handles unbalanced (mono jacks) and balanced (stereo jacks) correctly, automatically adjusting the level reference.
When using unbalanced cables with TRS jacks: be sure to connect the 'ring' contact of the TRS jack to ground. Otherwise noise may occur, caused by the unconnected negative input of the balanced input.

Inputs 3/4 operate in perfect harmony with the rear inputs 5 to 8, as they use the same level references:

Reference 0 dBFS @ Setting 3/4
Lo Gain +19 dBu Pad
+4 dBu +13 dBu No Pad
-10 dBV +2 dBV Inst
------- +8 dBu Inst + Pad

Instrument
The main difference between a line- and instrument input is the input's impedance. Via the option Inst 3 and Inst 4 in the Settings dialog, the input impedance changes from 10 kOhm to 470 kOhm. At the same time the input sensitivity rises to –10 dBV. Using active instruments this setting can already cause overloads. Therefore the option Pad is still available, reducing the
sensitivity by 6 dB.

The instrument input operates servo-balanced, thus handles balanced signals correctly as well.

Input Gain
Via Input Gain in the Settings dialog, or using the rotary encoder on the front, an additional gain can be applied to the input signals of channels 3/4. The gain range is 0 dB up to 18 dB, in steps of 0.5 dB. This option not only allows to use sources with low level output signals, but for example also to adjust the balance between channel 3 and 4 precisely, already before the recording takes place.

Overall the inputs 3/4 can work with levels from –16 dBu up to +19 dBu. Two LEDs display a present signal (from –65 dBFS on) and warn against overload (-2 dBFS).


What is the best way just to connect the two and get the best possible sound and bypass the Fireface preamps? I'm confused by all this jargon!
Old 28th January 2007
  #2
Lives for gear
 
DrDeltaM's Avatar
 

Use balanced XLR +4dBu out to TRS line in set to +4dBu reference level.
Old 28th January 2007
  #3
Gear Maniac
 
Jbassist's Avatar
 

Realy.. realy dumb question maybe.. but what is the big difference between working/recording in -10DBV or +4DBu?
Old 28th January 2007
  #4
Lives for gear
 
DrDeltaM's Avatar
 

Quote:
Originally Posted by Jbassist View Post
Realy.. realy dumb question maybe.. but what is the big difference between working/recording in -10DBV or +4DBu?
Just a matter of what you choose as reference level.

In general, -10dBV is used for prosumer, usually unbalanced gear. +4dBu is used for professional, usually balanced, gear.
Old 28th January 2007
  #5
Gear Addict
Doesn't the Goldmike have digital out? Why not use the spdif?
Old 29th January 2007
  #6
Here for the gear
 

Many thanks for that. Just one more question, or two! Does that mean I need a balanced XLR to TRS (stereo type jack) cable?

Can I simply use an XLR to XLR and set the FF400 input gain to 0? Or would this still make use of the FF400 preamps?

I'm afraid I dont have a digital out on the preamp.
Old 29th January 2007
  #7
Lives for gear
 
DrDeltaM's Avatar
 

Quote:
Originally Posted by steventucker71 View Post
Many thanks for that. Just one more question, or two! Does that mean I need a balanced XLR to TRS (stereo type jack) cable?
Yes, that's the exact cable you need.

Quote:
Originally Posted by steventucker71 View Post
Can I simply use an XLR to XLR and set the FF400 input gain to 0? Or would this still make use of the FF400 preamps?
That would indeed run thru the FF400 preamps, and it's not advisable to do with line signals.

Quote:
Originally Posted by steventucker71 View Post
I'm afraid I dont have a digital out on the preamp.
That's normal, the GoldMike doesn't have digital outputs standard, not sure if it's available as option, quite possible.
Old 30th January 2007
  #8
Here for the gear
 

Many thanks for your help! Works a treat.
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