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what kind of noise is this

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what kind of noise is this

Postby plodsmeade » Sat Nov 10, 2018 4:28 pm

Hi all

This is coming out of a Drawmer CMC2 fed from an Echo Layla 3G:

https://clyp.it/0kmpbvuo

The CMC2 and Layla are clean in isolation. The noise happens when patched with balanced or unbalanced cabling. The CMC2 has no ground on it's PSU.

I've unplugged everything else like HDs, visual monitors etc., as the intermittent nature of the noise might suggest something like that.

Any guesses?

cheers
p
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Re: what kind of noise is this

Postby Hugh Robjohns » Sat Nov 10, 2018 4:54 pm

What else is plugged into the monitor controller?

Is the computer grounded?

H
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Re: what kind of noise is this

Postby plodsmeade » Sat Nov 10, 2018 5:21 pm

Got the multimeter out and the IEC feeding the PC's PSU certainly is.
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Re: what kind of noise is this

Postby plodsmeade » Sat Nov 10, 2018 6:39 pm

Just saw your first question, and then also realised I hadn't tried unplugging the monitors (Focal CMS40).

Whether they are powered on or not, removing their IECs makes the intermittent stuff go away, as does removing their jacks from the CMC2.

Here's what it sounds like now with only the Layla connected to inputs 1 and 2:

https://clyp.it/rrvnnsve

This is with both the CMC2 headphone output and Layla preamps at max gain (with file about -40dBFS) so probably normal.

But, I distrust CMC2 in combination with my soldering now. I would normally assume the latter is the problem but the right headphone channel is not behaving if the PSU input is even delicately wiggled, cutting out or dimming, and wiggling of the jack inputs is not giving me repeatable results. Separate issue perhaps.
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Re: what kind of noise is this

Postby plodsmeade » Sat Nov 10, 2018 7:20 pm

Testing the loom I soldered just using the Layla out to in suggests it's rock solid for once.
Something's going on with the CMC.
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Re: what kind of noise is this

Postby Hugh Robjohns » Sun Nov 11, 2018 12:09 am

plodsmeade wrote:Just saw your first question, and then also realised I hadn't tried unplugging the monitors (Focal CMS40). Whether they are powered on or not, removing their IECs makes the intermittent stuff go away, as does removing their jacks from the CMC2.

I suspected as much. It suggests a ground loop between the monitors and computer.

Make sure both monitor speakers are powered from the same mains distribution plugboard as the computer to minimise the loop area. That might cure the noise problem on its own. If not, you may need to look at cutting and isolating the screen connections in the balanced connectors going into the speakers. Other options are available if those measures don't fix it

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Re: what kind of noise is this

Postby Martin Walker » Mon Nov 12, 2018 2:10 pm

Hi plodsmeade!

Hugh is (of course) spot on, but if you want a step-by-step guide to tracking down ANY ground loop problem then you may find my Q & A here of some help:

https://www.soundonsound.com/sound-advi ... -my-studio

The tricky thing often is that the noises are due to multiple ground loops, so solving one of them may not necessarily cure the whole problem.

In the most annoying cases, correctly breaking one ground loop may actually result in your overall ground loop noise going up rather than down (due to others still waiting to be solved), so sometimes you have to be extremely systematic :headbang:


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Re: what kind of noise is this

Postby plodsmeade » Wed Nov 14, 2018 1:05 am

Thanks for the tips. I will report back when I've had a chance to investigate further.

p
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