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RME User Forum → FireWire & USB series → XLR Input - Mic or Inst?
Hi, what is the best way to set up a couple of external preamps connected to the the front panel inputs on the Fireface series (XLR > XLR)? The line inputs at the rear are all in use and in my case it's an 802 interface. I don’t want phantom power, but I'm uncertain whether the XLR inputs should be set to ‘instrument’ or ‘microphone’ (with gain knobs all the way down) on Total Mix?
Thanks,
M
Both, XLR and TS work for line level sources. Maybe it’s more a question of what connection you prefer, balanced with XLR plugs or unbalanced with 1/4“ TS plugs.
Magic manual, page 38/39 tells:
19.2 Microphone / Line / Inst Front
The four sevo-balanced microphone inputs of the Fireface 802 use XLR/TRS combo jacks. A two colour LED displays present signal (green, from –46 dBFS) and warns against overload (0 dBFS).
XLR
The gain range of the XLR inputs is 54 dB, adjustable from +6 dB to +60 dB. This equals a sensitivity from +10 dBu down to -44 dBu, referenced to full scale of the AD-converter. The soft switching, hi-current Phantom power (48 Volt), switchable per channel, provides a professional handling of condensor mics. The usage of a hi-end integrated circuit (That 1510) guarantees outstanding sound quality, lowest THD, and maximum Signal to Noise ratio in any gain setting. Up to a level of +10 dBu, the front XLR input can also be used as Line input.
TS
The unbalanced TS Line inputs, which can be used alternatively, add even greater flexibility to the Fireface 802. With 800 kOhm input impedance (Hi-Z), TS jack and adjustable input gain over a range of 54 dB the front-side inputs can be used perfectly with keyboards, sampler, CD player, guitars and much more. These inputs handle levels from –33 dBu up to +21 dBu, turning them into full level Line inputs. Thus the unit can also be used as Line gain amplifier.
The TS jacks are free of phantom power.
Thanks for the reply. Yes, I prefer an XLR input. What I'm wondering is whether an XLR input channel should be set to 'Instr' or not in Total Mix when connecting an external preamp, or does it make a difference? There doesn't seem to be an audible difference to the sound when I toggle 'Instr' button on and off in Total Mix. Because I'm already applying gain with the external preamps, should I enable the orange 'Instr' button in Total Mix in order to bypass the Fireface's own mic preamps? Or do I just make sure the gain knobs are all the way down? In other words what is the best way to bypass the RME preamps while using the XLR inputs from an external preamp? Or is it possible?
Thanks again,
M
Don't set to "Instrument" this would gain up your signal a bit and you don't want that.
Let the gain closed thats fine.
The 'instrument' setting is for guitar and bass which always use TS cables, so the button only affects the TS input but not the XLR input I think. The preamps are not bypassed in every case (at least not to my knowledge).
You can experiment with different gain settings / combinations on your preamps and the FF802. If you have really good external ones, I would add more gain there and keep the 802 input as low as possible. With weaker ones maybe it would be better to use not too much gain there and add some dB at the 802 input.
Thanks you both for the replies. I think that you are right oli77sch and the XLR inputs are not affected by the 'Instr' switch in Total Mix. I will keep the gain on the 802 all the way down as I'm attached to the sound of my preamps. I just wanted to check my XLR inputs are set up on the 802 correctly.
Thanks for the feedback. I just want to be clear on this before I start a project. Most engineers would recommend connecting an external preamp to an audio interface using a TRS cable. I have my preamps connected to the front of my 802 using XLR cables. According to the 802 manual 'the front XLR input can also be used as Line input.' So as long as the gain is turned down on the 802, this connection should be fine then?
Thanks for the feedback. I just want to be clear on this before I start a project. Most engineers would recommend connecting an external preamp to an audio interface using a TRS cable. I have my preamps connected to the front of my 802 using XLR cables. According to the 802 manual 'the front XLR input can also be used as Line input.' So as long as the gain is turned down on the 802, this connection should be fine then?
Yes, it’s fine, no worries!
Most preamps have balanced line level outputs, some use XLR, others use 1/4" TRS plugs/sockets. The form factor of the plug doesn’t make a difference on the sound or the sound quality. Also in most cases it’s not a problem to use unbalanced connections, at least with short cable runs. So the TS input would be fine too. The 'proper' line inputs are on the back of the unit, balanced TRS.
Thank you for the reply. That's reassuring. I just looked at the 802 manual again and the full statement on this is "Up to a level of +10 dBu, the front XLR input can also be used as Line input." I'm pretty sure my preamps exceed this level! TBH I've never noticed any issues at all with the 802 using the XLR's input for my preamps, but perhaps going forward I should look at the rear TRS inputs to be on the safe side? Appreciate the feedback.
Going over + 10 will clip the input with an over warning. Easy to see and hear. No mythical loss. so no clip=no problem. Matching sensitivity, is for convenience, all meters will show the same, not for audio quality. In your case watch the rme meters, not the preamp, or both, but watch the rme for overs.
Thanks for the reply Vincent. I haven't had any overs on the 802 meters, so all good. I might try the TRS inputs just to compare.
Thank you for the reply. That's reassuring. I just looked at the 802 manual again and the full statement on this is "Up to a level of +10 dBu, the front XLR input can also be used as Line input." I'm pretty sure my preamps exceed this level! TBH I've never noticed any issues at all with the 802 using the XLR's input for my preamps, but perhaps going forward I should look at the rear TRS inputs to be on the safe side? Appreciate the feedback.
On the TS you could go up to +21dBu, worth to try this too. Make sure your ext. preamp accepts unbalanced connections on its output and use cables female XLR -> TS with XLR pin 3 ('cold') connected to 'ground'. I often use the TS inputs on my Babyface pro for preamps with balanced outputs and never had issues.
Great stuff. Thanks oli77sch for the tip!
Fyi, all will sound the same, it is just electrical levels into the same signal path
The output on external mic preamps is line level
no matter the type of plug or if its balanced or not.
Use instrument (HiZ) input for guitar or bass, for example,
which have passive pickups, and everything else
with active electronics is line level signal.
If you input consumer level products (HiFi gear, a mobile phone, etc.)
in the interface, set the gain in TM appropriately to -10 dB,
and for pro audio (studio) gear set it to +4dB.
That will give you the proper headroom for the signal.
I'm not sure if when the gain on the mic preamps on the interface
is all the way down that it bypasses the preamps when line level
signal is used or if it goes through the preamp circuitry nevertheless.
Some interfaces have that bypass.
RME User Forum → FireWire & USB series → XLR Input - Mic or Inst?
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