• Registered: 2023-01-02
  • Posts: 3

Topic: UFX II: Noise when line level signal connected to instrument input

Problem:

Quiet but audible high-pitched noise when Oberheim Matrix 6R line output connected directly (via unbalanced cable) to Mic/Inst input 9 of RME Fireface UFX II. Oberheim and UFX II getting power from same circuit.

Page 38 of the manual (https://www.rme-audio.de/downloads/fface_ufx2_e.pdf) indicates that the UFX II should be able to handle this scenario without issue:

The unbalanced TRS Line inputs (R is connected to ground), which can be used alternatively,
add even greater flexibility to the Fireface UFX II. With 1 MOhm input impedance (Hi-Z), TS jack
and adjustable input gain from +8 dB to +50 dB, the front-side inputs can be used perfectly with
keyboards, sampler, CD player, guitars and many more. They handle levels from -21 dBu up to
+21 dBu, turning them into full level Line inputs. Thus the unit can also be used as Line gain
amplifier.

Input Channel Settings:

Mic/Inst input 9 set to Instrument: On. Preamp Gain: +8db. Autoset Gain: On.

Output Channel Settings:

Monitored via headphones (AKG-K240) connected to Phones Out 11/12. Output Level: Lo. Volume: +6db.

Troubleshooting steps:

The following steps suggest that the problem is isolated to the scenario described in the above problem statement.

  • Swapped unbalanced cable w/ balanced cable, no change

  • Routed same source signal to Mic/Instrument 11 input, no change

  • Swapped source (Matrix6R synth line out) w/ another source (Roland MKS-50 line out), no change

  • Swapped line-level source (Matrix6R synth line out) w/ a headphone-out source (Matrix 6R synth headphone out) output, adjusted gain, noise disappeared

  • Swapped line-level source (Matrix6R synth line out) w/ an instrument-level source (electric guitar) output, adjusted gain, noise disappeared

  • Swapped line-level source (Matrix6R synth line out) w/ a mic-level source (Shure SM57) output, adjusted channel type & gain, noise disappeared

Question:

Is this behavior unexpected (as the manual suggests), or expected?

  • Registered: 2016-06-14
  • Posts: 1,142

Re: UFX II: Noise when line level signal connected to instrument input

Hi!

Only guessing, I would say the Oberheim has unbalanced line outputs. So a balanced cable wouldn’t make a difference on the also unbalanced instrument input 9 (-12) on the UFX. Anyway after swapping cables you know, it’s not only a bad cable causing the noise.
Because the problem persists on input 11 I would think the problem comes from the synth, but then you say the noise is also there with another synth plugged in…?
I would go further with troubleshooting and test the synth line out plugged to a 'real' line input (1-8).

UCX - FF 400 - Babyface pro - Digiface USB - ADI-2 (original)
Mac mini M1 - Macbook pro - iPad Air2
  • Registered: 2023-01-02
  • Posts: 3

Re: UFX II: Noise when line level signal connected to instrument input

Hi!

The noise disappears when connecting this same setup to a "real" line input 1-8.

  • Registered: 2016-06-14
  • Posts: 1,142

Re: UFX II: Noise when line level signal connected to instrument input

t8dogg wrote:

Hi!

The noise disappears when connecting this same setup to a "real" line input 1-8.

I’m not an expert but maybe the issue is related to the impedance then. Question: are the inputs 9-12 on the UFXII switchable between line and instrument?

UCX - FF 400 - Babyface pro - Digiface USB - ADI-2 (original)
Mac mini M1 - Macbook pro - iPad Air2
  • Registered: 2023-01-02
  • Posts: 3

Re: UFX II: Noise when line level signal connected to instrument input

No, inputs 9-12 are switchable only between mic and instrument (not between line and instrument). But because the manual says:

With 1 MOhm input impedance (Hi-Z), TS jack
and adjustable input gain from +8 dB to +50 dB, the front-side inputs can be used perfectly with
keyboards, sampler, CD player, guitars and many more.

I am under the impression that the UFX II should support this use case without noise.

  • Registered: 2020-08-14
  • Posts: 109

Re: UFX II: Noise when line level signal connected to instrument input

Hey there! I am experiencing similar, with Nord rack 2! lesser noise through Line In 7,8 instead of mic/inst in of 11/12.

Would you know why..?