Mackie VLZ4 sound issues

Be_LL

Member
We bought this mixer a few weeks ago as a bargain for a small church.
For some reason the headphones jack doesn't seem to work at all (3 different pairs tried so far)
And there's an annoying humming noise (unbalanced output) which to me seems to get louder after some 30 minutes of use.
The balanced output makes even more humming noise but i don't have any balanced cables to use between mixer and the amplifier (the amplifier doesn't take balanced inputs anyway).
Any idea what to look for? I'll try open it myself.
 

Attachments

  • 20210403_104926.jpg
    20210403_104926.jpg
    612.9 KB · Views: 73

DrewE

Well-Known Member
My unsolicited opinion: It is not worth much time to fix, unless you're going at it for the sake of the fixing process rather than the end result. You will probably have to remove every knob and screw and nut from the front panel to extract the PC board and see much of anything, and that in itself is rather time-consuming. (For these small mixers, there's usually just a single planar PCB with everything mounted on it.)

The headphone output problem might just be the connector, but I'd guess you might have a destroyed headphone amplifier chip, perhaps from trying to drive a shorted pair of headphones at some point or some other sort of (inadvertent) abuse. There are, of course, other possibilities as well. The humming could be from a great variety of causes. Is it reflected in the level meters? Is the hum affected by any of the controls? Is it present in any of the other outputs? Does it go away if inputs are disconnected? Are you using balanced cables between the mixer and the (unbalanced) input of your amplifier?

If you do get it open, check the obvious things first: are the power supply rails all correct and clean? Are there any obviously damaged components (e.g. chips with a crater hole, vaporized resistors, etc.)? Can you find any cracked or broken solder joints, after careful scrutiny?
 

FMEng

Well-Known Member
Fight Leukemia
With an unbalanced output connection, it's hard to tell whether the mixer is at fault, or it's just a ground loop. Try running the mixer from the same power AC outlet as the amplifier, even if that means running an extension cord.

Knowing a few more details might allow us to offer better suggestions. What model of amp are you driving and how far away from the mixer is it? Is the mixer used, or still in warranty?

As far as the headphones go, you did engage the "main mix" button, right?
 

TimMc

Well-Known Member
Premium Member
The most likely culprit: power supply failed and took out the headphone amp chip and is also why you have a nasty hum, pretty much everwhere.

Solution: e-recycling.
 

Be_LL

Member
User error here for headphones. I was keeping the Control room outs OFF.

I'm not sure what brand that amplifier is. However was installed by professional supplier, in an enclosure. There are: wireless receiver for 2 microphones, amplifier and some other unit, speakers installed in all 4 corners near ceiling. Was installed by the landlord as a permanent system.
We only connect to that through an AUX port built on the top of enclosure, a TRS female connector, and we use our own mixing machine.

All power is taken from the same socket, well our equipment is plugged into an extension cable. The extension cord is a cylinder and only half unwound (won't melt at the level of power used by us) 🤔
 

Be_LL

Member
I can only attend the venue once a week at the moment. I retrieved the mixer at my home for the week. There's no humming through headphones. And through my soundbar (that's all what i have at home) sounds just fine, only the regular hiss when your turn everything all the way up.
 

FMEng

Well-Known Member
Fight Leukemia
The Mackie is OK then. The hum is probably just a plain, old ground loop, which could happen with any kind of mixer. Since troubleshooting access, to both the venue and the amp rack are limited, I'm going to jump ahead. Buy a Morley MHE and insert it between the mixer output and the amplifier input.
https://www.sweetwater.com/store/detail/HumElim--morley-mhe-2-channel-stereo-hum-eliminator

Put the MHE at the amp rack, and use a 2-3 foot cable from the MHE to the amp. Use an XLR-XLR cable between the mixer and MHE. No guarantee, but this is pretty likely to fix it.
 

Be_LL

Member
Thanks for suggestions. Apparently Morley MHE is available only from US, it will be way too much with postage and taxes shipped to my country. I've found an alternative here, Behringer microhd HD400.

However I've manage to check the amplifier and connections.
Is a TOA PA A-2120 as picture attached. The available input left for us is actually a microphone input. The 1/4 jack inserted into amplifier is TS only, cable is a dual core shielded and wired as balanced to an external fitted female jack TRS...

We were trying to send a dual channel (stereo) into that 🤦‍♂️🤦‍♂️...

Is it possible to send Mackie outputs into an amplifier microphone input ?
 

Attachments

  • Screenshot_20210410-143114_Adobe Acrobat.jpg
    Screenshot_20210410-143114_Adobe Acrobat.jpg
    738.9 KB · Views: 46
  • Screenshot_20210410-143156_Adobe Acrobat.jpg
    Screenshot_20210410-143156_Adobe Acrobat.jpg
    904.9 KB · Views: 47
  • 20210410_123028.jpg
    20210410_123028.jpg
    264 KB · Views: 34
  • 20210410_122859.jpg
    20210410_122859.jpg
    250.4 KB · Views: 36

DrewE

Well-Known Member
You have a few cabling issues, as you've observed.

Sending a stereo signal to a mono amplifier is of course not going to work very well if at all. The simplest solution is to simply ignore either the left or the right output of the mixer (and make a mental note that an input panned to the opposite side isn't going to work).

Sending a balanced signal to an unbalanced input is also not going to work reliably sometimes if the cable is improperly wired up. Somewhat insidiously, it may work fine in some cases, depending mainly on the exact output circuitry of the source: if it's an impedance balanced circuit, then you can get away with it. I kind of suspect this might be the source of your problems, actually, though I could well be wrong about that.

Connecting the mixer output to a microphone input requires an attenuator (and, in the case of a microphone input with phantom power, something to block that). One simple way to accomplish that, albeit with further unbalanced/balanced concerns, is to insert a passive direct box with an attenutator between the output the input, engaging the attenuator as required. This can also take care of blocking any phantom power and help with eliminating any ground loops.

I'm guessing your speaker system is a 70V or other high impedance setup? If so, it might be worth thinking about using some other speakers and amplifiers (if not active speakers) for sound reinforcement, as many 70V systems are not especially high fidelity--great for background music and paging, not so great for performances. There are exceptions, of course, and matching the speaker system to the room acoustics is also something to be concerned with.
 

FMEng

Well-Known Member
Fight Leukemia
The input on the Toa amplifier is balanced, mic level, with a TRS phone jack. The Mackie can drive that directly. Use one of the XLR main outputs on the Mackie. Engage the "Main Output Level" switch on the mixer, which lowers the output to mic level. The cable between the mixer and amplifier should be an XLR female to TRS phone plug. By using a TRS plug directly into the back the amp, the connection will be balanced, which substantially reduces the chances of having any more hum.

If you need to use the unbalanced jack on the enclosure instead, then add the Behringer Micro HD400, and use the single XLR output and engage the main output level switch, as outlined above. The cable between the HD400 and the enclosure jack must be TS to TS.
 

DrewE

Well-Known Member
The Mackie can drive that directly. Use one of the XLR main outputs on the Mackie. Engage the "Main Output Level" switch on the mixer, which lowers the output to mic level. The cable between the mixer and amplifier should be an XLR female to TRS phone plug. By using a TRS plug directly into the back the amp, the connection will be balanced, which substantially reduces the chances of having any more hum.
I didn't realize the mixer had this capability built-in; but that makes things much simpler. Please ignore most of what I wrote and follow what FMEng said above.

(Another family of little mixers that have the ability to set the main outs to microphone level via a built-in attenuator are the Allen and Heath Zed mini series: the Zed 10, Zed 10fx, Zed60-10fx, and Zed60-14fx. It's such a handy and simple little feature that I'm rather surprised more small mixers don't have it.)
 

TimMc

Well-Known Member
Premium Member
I didn't realize the mixer had this capability built-in; but that makes things much simpler. Please ignore most of what I wrote and follow what FMEng said above.

(Another family of little mixers that have the ability to set the main outs to microphone level via a built-in attenuator are the Allen and Heath Zed mini series: the Zed 10, Zed 10fx, Zed60-10fx, and Zed60-14fx. It's such a handy and simple little feature that I'm rather surprised more small mixers don't have it.)

It's a case of customer satisfaction > than preferred engineering. Putting a -30dB pad, only to add +30dB gain at the other end of the wire makes engineers wince, a lot... but it makes customers smile because the "fix" becomes appliance-simple.
 

FMEng

Well-Known Member
Fight Leukemia
An XLR to XLR pad costs about $30. It's a handy thing to have in the audio adapter kit. -40 dB is about right most of the time. Whirlwind, RapcoHorizon, Pro Co, and Shure make them, among others.

There are plenty of places where driving a mic input with a mixer makes sense. For example, I've done shows in a nice, 800 seat, college lecture hall, where there was no mixer and the student techs weren't allowed to do much more than turn the system on and adjust the volume. I just told them to show me an active mic jack and plugged my mixer into it with a pad and a Jensen isolation transformer. I was prepared to hand the kid a couple of 20s if they gave me any push back.
 

Be_LL

Member
Thank you people! I've ordered the right cable extension (some 5m). Also I've seen the Main Output Level switch on the mixer but is inside and most probably you need a pen to press it. At first look to me it seemed like a blanked hole. I will make some tests again this week (hopefully) and get you updated.

I've learned a lot 🙏🙏
 

Be_LL

Member
Quick update. All works as it shoud now.
I've replaced the short cable inside the box with a man made one and still getting a whizzing sound when using that for some reason, however i can by-pass that and use the 5m balanced cable straight into amp mic input and works just fine in this way.
 

Attachments

  • 20210417_104518.jpg
    20210417_104518.jpg
    217.9 KB · Views: 30

Users who are viewing this thread