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Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

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Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Fri May 17, 2019 6:52 am
by tardis58
I have 2 small Mackie Mixers Mackie: 402-VLZ3 and a second that I currently don’t have the number for but is slightly bigger.
They both work well but intermittently produce a suddenly loud repeated banging or thumping noise, that would continue for hours if ignored and sometimes disappears if the units is turned off for a period.
There is no consistency in the set up.
There is no obvious error in settings or use.
We think it only occurs if there is a feeding source possibly a laptop or phone.
But it’s infrequent and hard to pin down.
Has anyone experienced similar?
Anyone any idea what it is and how we can prevent it?
Thank you

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Fri May 17, 2019 10:21 am
by Hugh Robjohns
tardis58 wrote:I have 2 small Mackie Mixers Mackie: 402-VLZ3 and a second that I currently don’t have the number for but is slightly bigger.
They both work well but intermittently produce a suddenly loud repeated banging or thumping noise...

The fact that it happens with two different mixers means that it's unlikely to be a mixer fault -- the chances of exactly the same fault happening on two different devices at the same time is very slim.

So I'd be looking at external factors: namely, the signal source, the mains power supply, and the speakers or whatever the mixer is connected to.

We think it only occurs if there is a feeding source possibly a laptop or phone.

There you go... investigate that idea more thoroughly. Does the noise go away when you disconnect that source?

If so, is the noise an inherent 'feature' of that source, or is it due to the way it's connected?

For example, could it be related to the phone or laptop polling for a wifi signal or checking other online accounts, or checking in with a local telecomms mast?

Could it be that it is connected to a mic input with phantom power turned on? Could the phantom volts be overwhelming the device's output circuitry (eg, reverse-biasing output capacitors) after a certain time? If so, connecting via a DI box might well help.

Intermittent faults or problems are always the hardest to resolve... You first need to be able to make the fault happen reliably!

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Fri May 17, 2019 6:19 pm
by tardis58
Very careful and helpful reply.
But my colleague and I have now reproduced the error in 5 or 6 locations with completely different setups. Sources and amp speaker configurations.
The phantom power is a good call but does not appear to make a difference.
The fault is now consistent every night and seems more likely when it’s on for a protracted time.
It also appears to stop if you turn off power source and turn on again.
Please keep thinking.
As it’s more consistent we may have more chance to analyse it.
I’m going to ask for it to be left on tonight and we may get a chance to review tomorrow.
It has been very variable.
We agree that happening in two different mixer from the same company appears very unlike
Unless there is a common glitch

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Fri May 17, 2019 11:16 pm
by James Perrett
Sounds similar to an issue I had with a reverb unit. It would work fine for hours and then you'd hear a rumble or sometimes a big crack before it went back to working fine. I still haven't fixed it but as far as I can tell it seems to be coming from one of the op amps close to the input.

It does seem strange that the same thing has started to happen on two different mixers at the same time - I'm just wondering whether it might be interference from a powerful radio transmitter. Are there any local radio amateurs or CB enthusiasts?

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Sat May 18, 2019 12:30 am
by Eddy Deegan
Hugh Robjohns wrote:
tardis58 wrote:We think it only occurs if there is a feeding source possibly a laptop or phone.

There you go... investigate that idea more thoroughly. Does the noise go away when you disconnect that source?

I think this is worth re-emphasising. Were you able to confirm whether or not the noise is only evident when a source is connected to the mixer(s)?

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Sat May 18, 2019 7:53 am
by tardis58
I think it is only present when there is a source connected.
Various sources

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Sat May 18, 2019 10:18 am
by Hugh Robjohns
tardis58 wrote:I think it is only present when there is a source connected.
Various sources

In which case you need to explore those sources and the way they are connected more carefully.

Unbalanced connections are notorious for suffering problems with ground-loops and rely upon a clean ground reference. Any noise on the mains power safety earth can be added to the wanted signal, as can external interference from nearby radio transmitters etc (including nearby hand-held walkie-talkies.

So how are you connecting whatever you are connecting?

H

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Sat May 18, 2019 9:11 pm
by AlecSp
Have you eliminated the problem being with downstream kit, say the amplifier/active speaker that the mixer is feeding.

Once a problem is occurring, pinpointing it is all about removing bits of the signal chain and seeing which the fault follows. To test the above, try using an alternative amp/active speaker - also try listening on headphones.

This is pretty basic stuff, and should be obvious. It never ceases to amaze me how few people think to do it. Like guitarists with big pedalboards and sound problems who don't start by just plugging the guitar straight into the amp, and then working backwards through the pedalboard.

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Sun May 19, 2019 6:23 pm
by tardis58
Logical reply
But all components have been changed in a diversity of ways.
active speakers , amplifier, short cables, long cables.
Balanced unbalanced to the amp/speakers.

Various sources.

Presumably I’ll be criticised but the source is often via a short unbalanced cable from a laptop or phone or iPod. Mini jack to 2x phono.

Yeh not perfect but a very common source I’ve used thousands of times and has never produced this thumping sound before with other mixers or systems

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Sun May 19, 2019 6:54 pm
by Hugh Robjohns
See my post above.

Unbalanced connections are notorious for problems like this, although I've frequently plugged the headphone outputs of phones and iPods into unbalanced stereo line inputs on my own 1402vlz Mackie console without any problems. So you'll hear no criticism from me for trying to do that!

However, you seem to saying the thumps happen with multiple different unbalanced sources, and that suggests to me that the problem is related to a local source of intermittent interference and/or disturbances to the mains supply.

The only way to track problems like this down is to work through the system very methodically until you can reliably and consistently identify exactly where the unwanted noises are getting in to the system. It takes considerable time and patience and requires a solid understanding of the electrical interfacing arrangements between the different items of equipment.

So, are the amps/speakers thump-free on their own? If so, connect them to the mixer (or driver rack etc) using balanced cables. Quiet? Then connect sources to the mixer, one at a time...

Once you have positively identified where the noises are coming from you can work out whats causing it and come up with a solution.

But working on the previous basis that its coming from your unbalanced aources, a worthwhile experiment to try would be to connect the unbalanced source to the mixer via a transformer isolator box -- I like to use the ART DTI -- and from that box to a balanced stereo line input using balanced cables. Alternatively, use a DI box and connect via a pair of mic inputs. Does that make any difference?

Re: Thumping/Banging noise on two different Mackie small mixers. Mackie 402-VLZ3 and a larger one

PostPosted: Sun May 19, 2019 9:13 pm
by Mike Stranks
Are there perchance any radio mics in this equation? If so, what make/model?