• Registered: 2022-04-15
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Topic: Settings for connecting a high end mic pre to RME Fireface 800

I have just purchased a high end mic pre (Great River NE-1NV) which I will be connecting to a rear input of my RME Fireface 800 using a balanced cable (XLR to balanced ¼ inch). Apart from the RME, there is no other hardware in the chain between the Great River preamp and my computer (PC with Cakewalk as my DAW).

My question is which setting on the RME unit should I choose for optimum performance and sound quality in this situation? Should I choose +4dBu or -10dBV for the RME input (There is also the third option of Lo Gain). And which setting for the output?

This subject of “+4dBu or -10dBV” has always confused me, despite having done some research on it. I stated "high end mic pre" only to distinguish it from "consumer level" equipment, which some say is best suited to -10dbV. I hope someone can offer some advice.

2 Reply by ramses (edited by ramses 2022-04-15 10:10:46)

  • ramses
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Re: Settings for connecting a high end mic pre to RME Fireface 800

Different standards exist for connecting different types of analog audio equipment with different connection types and signal levels.

Reference levels: Consumer level at -10 dBV (0.316V) for devices like CD/DVD players. Usually in studios (but nowadays also to be found in the HiFi world) you find higher audio levels +4 dBu (1.23V) or significantly higher up to +24dBu.

Regarding cable connections, best is to use balanced cables to have more protection against electrical noise.
There are two plug standards supporting balanced (three wire) connections:  XLR and TRS.
IMHO best is using XLR plugs (from Neutric) in terms of stability / plug design and they are lockable.
Some inputs can be switched to be used for connecting instruments like guitar bass using TS plugs called Instr or Hi-Z.

Balanced connection carry the audio signal in two polarities (+/-) and have a circuit to eliminate the differencies (noise) and having a higher signal (studio levels), which makes it possible to use longer cables.

Your FF800 is best designed to connect any type of analog gear by having line inputs, supporting balanced and unbalanced connections (with different reference levels) and unbalaned instr/"Hi-Z" inputs as well as outputs for headphones.

More information to that see manual ch 21 (inputs), ch 22 (outputs), ch 29.1 (technical section).
https://www.rme-audio.de/downloads/fface800_d.pdf
https://www.rme-audio.de/downloads/fface800_e.pdf

When connecting other equipment to an analog input the goal is to choose an input level, so that the connected device does not overload the analog input of your recording interface, otherwise you will get distortion. But you also do not want to choose a reference level that is intended for hotter signals, then you will end up with a too low input signal for recording with less dynamic and lower SNR.

Check your mic preamp's manual. It will surely support balanced connections and the typical studio level +4dBu.
Set the analog input of your FF800 to a matching reference level, most likely both devices will support +4dBu.
Your Mic preamp has a knob to adjust the output volume. You can use this to perform adjustments.
Dial in an output volume so that you have enough headroom before 0dB.
If you think the output of the preamp appears too hot, try the next higher reference level "Lo Gain".
Most likely the input signal will be too silent, then go back to +4dBu

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13
  • Registered: 2022-04-15
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Re: Settings for connecting a high end mic pre to RME Fireface 800

Thank you, Ramses, for taking the time to give such a detailed response. The advice you have given seems to make sense.

I have to wait for a shipment of Mogami balanced cables before I can properly test the levels of the Great River preamp. I’ve only had the preamp for two days, and at the moment I can only use an unbalanced XLR to 1/4 inch cable from the Great River pre to the FF800. With the unbalanced cable and the FF800 at +4dBu, the signal is pretty hot/high—a lot higher than when I use the FF800 onboard mic pres.

The Great River manual doesn’t specify +4dBu, but it does have the choice of an unbalanced (1/4 inch) and a balanced (XLR) output. The manual only states that for the balanced out the “XLR pin 2 is hot”. For the unbalanced it says “1/4 inch -10dBv”.

I think I will wait for the Mogami cables to arrive, and if the signal is still high I can try what you suggested—the Lo Gain setting.

Thank you again.

  • ramses
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Re: Settings for connecting a high end mic pre to RME Fireface 800

Telarco wrote:

The Great River manual doesn’t specify +4dBu, but it does have the choice of an unbalanced (1/4 inch) and a balanced (XLR) output. The manual only states that for the balanced out the “XLR pin 2 is hot”. For the unbalanced it says “1/4 inch -10dBv”.

I think I will wait for the Mogami cables to arrive, and if the signal is still high I can try what you suggested—the Lo Gain setting.

Thank you again.

Manual: Gain Staging
The NV Series preamplifiers offer comprehensive gain staging capabilities, controlled by two
knobs on the front panel. The large gain knob adds an increment of 5db of gain with each step,
while the small output knob, the pot, delivers continuous adjustment of the output level. The
input range of the large knob is 0db to 60db and the output range of the small knob is
approximately -22db to +10db relative to the "CAL" marking on the front panel. The overall
maximum gain is 70db in the 1200 ohm input impedance mode.
Great River Tips:
Generally, the signal will be affected the least by keeping the large knob turned down and the
small one up. More coloration occurs when the input stage does most of the work, so cranking
the large knob and trimming back the output control will tend towards a thicker sound. When
the input stage clips, it gets ugly, so keep an eye on it.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13
  • Registered: 2022-04-15
  • Posts: 6

Re: Settings for connecting a high end mic pre to RME Fireface 800

Yes, there is a lot of scope for adjusting levels using the input gain and the output level controls. A welcome feature is also the separate input and output level meters.

When I said I was getting a hot signal, I meant relative to what the meters on the Great River preamp were telling me. When they were at what I thought was quite a safe level, the levels in my DAW were occasionally exceeding zero db. But this is most likely because I was outputting from the balanced XLR jack using an unbalanced cable (an old mic cable I’ve had for years that has an XLR connecter on one end and a ¼ inch connecter on the other).

I think it’s best that I wait for the proper balanced cable to arrive and then I can get serious about testing levels. Your response to my question, Ramses, and some further reading, has given me a good starting point by knowing that +4dBu is the recommended setting for the FF800.