M3700 Noise on main output (resolved)

[Baal Prod Studio]

Hi everybody, here is my problem. When I listen to a channel by control room (A or B), there is a background noise. When I listen to the same source in the solo mode (main fader at the same position), the noise disappears. Have you an idea about that? Thank you for your replies!

 

[witzendoz]

When you listen to the main outputs you are listening to the sum of all the inputs, is solo mode you are only listening to the channel input. Are you talking about noise that goes up and down with the channel fader or the total noise of the whole mixer?

Alan.

 

[Baal Prod Studio]

Thank you for your reply Alan. The 32 faders are down. I just open the main fader and it's noisy. If I switch on a solo button (always with the 32 faders down), the noise disappear. I haven't this problem with the M3500...

 

[witzendoz]

What is the noise like, hissy, spiky, hum?

Try muting all the aux sends and monitor faders, not just turn them down, does the noise reduce or go away?

Alan.

 

[Baal Prod Studio]

Hi Alan thank you for your help, I muted all channels and aux sends, faders down. When I listen by the stereo outputs all is good (the sound comes directly from the main fader). When I listen by the control room (a or b), the noise appears when I up the volume, turning the CR knob... It seems that the problem comes from there.

 

[witzendoz]

What type of noise is it?

 

[Baal Prod Studio]

It's a sort of buzzing sound with several different frequencies simultaneously...and only when I open the control room knob. So, it can't be a ground problem.

 

[witzendoz]

There could be a problem with the outputs on the desk, however there could be an issue with the connections, what are you plugged into? Power amp, active monitors<, balanced or unbalanced wiring?

Alan.

 

[Baal Prod Studio]

Today, I just tested the earphones output, without wiring. I turned on the earphone knob at middle position, and the main fader at 0 . The buzz was there. After that, I pressed the CR button on. The buzz was there too. And finally I pressed a solo button on, no more buzzing sound... (Solo knob at middle position).

 

[witzendoz]

Sounds like there is an open unshielded circuit somewhere in the console that is bypassed when the solo is on.

I assume you are doing these tests with everything muted (manual not automation mute) channel faders, aux faders, monitor faders, effects return faders? Also talking of automation, is the automation bypassed while you are doing this? Just in case it's the automation side causing the problems.

Make sure also that there is not a whole load of line inputs turned up full and all feeding the master bus.

You may have to get a tech in to have a look at this problem.

alan.

 

[Baal Prod Studio]

Sorry for my late reply and thank you very much for your help Alan. I was touring these last weeks and was very busy. I called a tech. He will come next week.
Michel

 

[Baal Prod Studio]

I'm back from Boston, and last week a technician went in my studio. The problem was not the mixer but the xlr between the mixer and the amp. He just disconnected the ground on the 2 xlr, and now, all is working in silence! Thank you so much for your help Alan.

 

[mrconfuse]

Sounds like there is an open unshielded circuit somewhere in the console that is bypassed when the solo is on.

I assume you are doing these tests with everything muted (manual not automation mute) channel faders, aux faders, monitor faders, effects return faders? Also talking of automation, is the automation bypassed while you are doing this? Just in case it's the automation side causing the problems.

Make sure also that there is not a whole load of line inputs turned up full and all feeding the master bus.

You may have to get a tech in to have a look at this problem.

alan.

Hey Alan,

looks as I have the same behavior as mentioned by Baal Prod Studio, but the cables are not the problem. I have tested different ones an also disconnected the ground of the xlr cable I used.

No matter what my Control Room has hum and noise. When I Solo just one Channel it is gone. When I solo all channels the hum and noise returns, but not as intense as it is when the CR is on without solo (I tried to measure equal level CR gain and Solo gain with a signal).

Could this really be an open unshielded circuit somewhere somewhere in the console?

A friend of mine came up with the thought that the control room amplifier maybe has a
capacitor that is not working anymore. Is that valid thought?

Should I check the PSU if there is something not working right?

Martin

 

[witzendoz]

I am assuming that you did all the things I talked about earlier in the thread, muting the sends etc,

The earthing stuff between the amp and the mixer, lifting the shield etc, can also happen between the mixer and the recording equipment. What is connected? A tape machine or an interface.

I am connected to a Tascam MX2424 hard disk recorder, previously and now occasionally I connect to a Tascam MSR16s tape machine. Between the Console chassis and the chassis of the MX2424 / Tape machine, I connect a thick earth cable. The background hum reduced to about 10% of what it was, this however is trial and error.

You also have to look at disconnecting shields on the cables connecting this gear to the console.

I also have a computer (interface) connected to the console for when I mix to stereo using the console. This used to cause a slight buzz, I placed isolation noise filters on the in and out lines to the interface and they are now completely silent.

Also a side note, I recently put a large screen TV on the wall and connected the HDMI to the computer, we can now see the recording wav forms easy while tracking. However the TV caused a buzz on the console, until I tried it on a different power outlet and it went away. This shows how fickle the power and earthing is within the studio.

Let me know how you go.

Alan