

aviorrok wrote:The noise appears only when the analyzer button set to post, when the button set to pre there is no noise.
aviorrok wrote:The noise appears only when the analyzer button set to post, when the button set to pre there is no noise.
hz37 wrote:Are you saying you can actually hear this as noise?
Dave B wrote:The fact that it is not there on the input means that the eq itself is more than likely causing the issue.
Hugh Robjohns wrote:As James commented above, I thought we had narrowed the problem down to the Warm preamp and a potential ground-loop or interference issue.
I suspect the fact that this ~20kHz tone appears only at 48k and higher as sample rates is due to unfortunate beat frequencies between the digital rig and something in the Warm preamp (switched mode PSU perhaps, or unintended self-oscillation maybe). Resolving any ground-loop problems may well make the HF tone disappear permanently.
H
Hugh Robjohns wrote:The fact that it only happens when the preamp is powered up suggests a fault with the preamp to me... since a simple ground-loop would be present all the time regardless of powering status. Which is what I thought we identified a while ago.
Having said that, the unwanted noise (from the preamp) would appear to be getting into the system via the grounding of the control line from the UPS.
If it's not already the case, I'd start by making sure the preamp is plugged into the same power outlet as the UPS since that will minimise the group-loop area.
After that, I'd try breaking and isolating the screen connection in the balanced cable from the preamp to the interface, ideally inside the TRS plug at the interface end. That will break the ground-loop -- if there is one -- and that might well help... but it really depends on where the interference is actually getting in to your system.
H
aviorrok wrote:I solved the problem
I connected the UR242 input to preamp output with XLR and not TRS and the noise is gone!
Maybe you know why?
Hugh Robjohns wrote:As James commented above, I thought we had narrowed the problem down to the Warm preamp and a potential ground-loop or interference issue.
Resolving any ground-loop problems may well make the HF tone disappear permanently
Martin Walker wrote:aviorrok wrote:I solved the problem
I connected the UR242 input to preamp output with XLR and not TRS and the noise is gone!
Maybe you know why?
Aha - then it does sound like a ground loop issue, as by moving from TRS to XLR connections you are now balanced and have broken the loop![]()
As Hugh said over a week ago:Hugh Robjohns wrote:As James commented above, I thought we had narrowed the problem down to the Warm preamp and a potential ground-loop or interference issue.
Resolving any ground-loop problems may well make the HF tone disappear permanently
Martin
aviorrok wrote:But th TRS is also a balanced cable am I wrong?
Also ground loop frequency is about 40-55Hz so I don’t think it’s a ground loop issue with the TRS
aviorrok wrote:I solved the problemI connected the UR242 input to preamp output with XLR and not TRS and the noise is gone! Maybe you know why?
Wonks wrote:Ground loop noise can be any frequency and is often quite high pitched.
Both the TRS and XLR outputs on the WA preamp are balanced, as are the front XLR/TRS combi inputs and rear TRS inputs on the interface.
The UR242 is a slightly funny beast in that both the XLR and the TRS on the combi inputs can be mic or line.
With the front inputs used as line inputs, the pad switch is supposed to be used to drop the signal level down so the preamp can then amplify it again.
Also, the TRS input on input 1 can be selected as Hi-Z
The rear line inputs 3 and 4 are balanced TRS and software switchable between -10dBu and +4dBV (-10 is the default).
So when using a TRS cable, aviorrok,
a) Was the pad switch engaged?
b) Was it plugged into input 1?
c) if b), was the Hi-Z switch engaged?
The only possible physical difference between the TRS and XLR inputs is the Hi-Z switch on input 1 . If that was in, then the WA output may be prone to picking up more interference. Either that or the TRS cable has a fault on it and is letting in noise.
So try the TRS cable on input 1, but with the pad switch in (if not already and ensure the Hi-Z switch is out (obviously the +48v power should be off).
If you still get the noise, but when using the XLR cable on the same input you don't have it, then either there's a bad connection to the TRS socket in the UR242, but more likely there's a problem with the cable.
I'd also try the TRS cable on inputs 3 and 4 (switching the mode to +4dBV first in software) to see if that works. This should determine if its a faulty XLR socket.
Personally I'd keep the WA plugged into one of the rear sockets, leaving the front ones free for easier access.
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