Humming noise since adding a vocopro DA-1050pro mixer to our system.Have connected a ground loop isolator but it makes no difference.The mixer is the only change in the system

I used to be a hi-fi enthusiast many years ago.
A low frequency hum can be caused by inadvertently creating a "hum loop". This is when audio separates are earthed or grounded where they are plugged into the power outlets and then connected together using screened audio leads where the screening is connected to both plugs.
The situation can become worse when one of the separates is a type that isn't grounded.

Ineffective or insufficient power supply smoothing and/or shielding leaving an AC ripple on the DC also creates a hum or in the case of poor design or bad shielding can radiate AC magnetism into the high gain input stages of amplification.

Whatever the cause of the hum it can be aggravated by poor matching of separates with regard to input/output sensitivities and impedances. If the pre-amp stage gains have to be high to compensate for a low input signal the signal-to-noise ratio will always be poor through every stage. Small signals requiring large amounts of amplification requires low impedance circuitry and appropriate sensitivity.

Food for thought...

First, check your levels on the console. Is anything turned up high, channels, gain settings on channels? Check and see if the noise exists whith the main outputs muted or turned down. If it goes away it is a fader or gain setting on a channel. If it persists, then you have a co nection issue with the USB . Try a different cable. Make sure the Mac is on the same electrical circuit as the mixer, or if it is on battery, try adding it on the electrical circuit with the mixer. See if location of the mixer to the computer makes a difference as well. They may be too close to each other. Hopefully one of these things will fixya.

Hello,

I need a bit more information but from what i can tell it's about the power supply capacitors issue, as this devices are known to develop such kind of humming annoying noise when they go under the specified value, let me know further,
Regards.

If it is a 60Hz or 120 hz hum, the fault may be a bad solder connection to a filter capacitor in the power supply.

If it is a hum like a bad mic connection, you may have dirty contacts on an input, dirty tracks on a mixer control, even on the EQ portion.

It may also be a bad cable is connected, or a 1/4 inch jacked input may not be grounding out when the plug is removed. You may have a bad ground on the power feed and you have a ground loop as a result, or a cable is faulty and creating it's pwn ground loop to something else.

Contact cleaner is not a bad idea, slide pots are notorious for spurious noise over time. LPS1 is not bad, but it does use silicone as the dry lubricant portion.

If all of that is ruled out, look internally for bad solder joints- anything that looks crumbly is suspect, and also check for loose wires and jacks with bad solder connections. Also look for loose connectors too.

Make sure you are using BALANCED audio interconnect cables AND that the speakers and the mixer are powered from the SAME receptacle... Yes, this means running extension cords. It is a ground loop problem. You should be using XLR or TRS cables BALANCED cables from the mixer to the basss unit of the L1 system. The bass unit and the mixer MUST be powered from the same receptacle to avoid ground loops and hum.

Make sure ALL of the interconnected equipment is powered from the SAME receptacle to avoid ground loops due to the safety ground. DO NOT Use two wire power or use ground lifting plug adapters. Make sure you use balanced lines, either XLR or TRS cables. Do NOT use TS cables.

This sounds like a ground loop. Make sure ALL (including the computer) interconnected devices are powered from the same receptacle. Make sure there are no lamp dimmers around as these can cause hum...

You need to solve a ground loop problem. Read up about DI's and ground-lift. The problem is circulating currents from the power line back to the system.

FIRST power ALL interconnected equipment from the same source. Do NOT run the keyboard from a stage plug that is different than what your board and amps run from for system safety.

For many situations you will want to use a DI very near the keyboard with ground lift setting. Then run XLR balanced line to your mixer board. You mixer aand all the amps and the keyboard need to be powered from a single receptacle or power conditioning module.

Try hooking your mixer up to your Mackies without the laptop. Does the hum go away? Try hooking your laptop output up to the Mackies without the mixer. Does the hum go away? Make sure that all your power cables run from the same outlet and have the ground or third pin intact on the plug. Also make sure that you are using shielded cables for any connection that carries an audio signal. This includes the cables going to your Mackies as they are powered amplified monitors. Make sure that the cables to your Mackies are balanced and haven't been altered to unbalanced. You will need to use unbalanced cables from your laptop unfortunately but try to find ones with a shield and three conductors ( right and left signals and a common or ground) that have a separate shield from the common. The shield should only be connected to common at the output of the device where the signal starts. A better explanation is at these links:http://www.epanorama.net/documents/groundloop/ also http://www.epanorama.net/documents/groundloop/cable_shielding.html

There are LED's all over these and you don't say which are lit... If they are mute or solo LED check the switches for a solo button or mute that is set.

IF they are the output level LED's plug in a set of phones and crank the phone volume up to losten if there is feedback or oscillation that is causing this.

HUM PICKUP due to a ground loop could be causing this. Make sure that ANYTHING connected to the unit that is also powered receives pwer from the SAME receptacle. If you have devices that receive power from a different receptacle you MAY have a ground loop. Noise on power lines can DAMAGE the equipment due to excedding the common mode input and output capability of the unit.

Finally, a strong local radio transmitter MAY be interfering. Sometimes the interference can go backward into the output lines to trigger the indicators.

As a test, when event occurs again, start unplugging anything connected to the mixer and see if disconnecting anything stops the problem. If you can have the problem with ONLY the power connected, then check if you have inadvertently created a loop within the unit by your settings.

Please refer to the "signal flow" diagrams in your user manual to see the possible feedback paths you can cause a loop to form.

REMEMBER the oscillation MAY be occuring well above the frequency you can hear !!!!

If you have access to an oscilloscope that would see if there is an oscillation going on.