Glensound Mixer intermittent noise.

[dimesav]

Hello Group Diy - first post here. Been browsing this site for a while now dreaming of potentially building a mixer but quickly realised it was a little above my capabilities.. so ended up purchasing a Glensound 8x2 mixer to fulfil stem mixing duties. All 8 channels of the mixer are working as should .. however there is a lot of noise sometimes which is triggered when the mixer is touched or tapped. I think the problem lies in the master section or is a grounding issue but not entirely sure.  I've attached the manual and a short video I made for a tech who is maybe a little busy to look at it.  Any help would be mucho appreciated!
ps kudos to all the regular contributors and folk sharing their builds. Great stuff.

All the best,

Rob

Manual: https://www.dropbox.com/s/ng8k7c87x75ops2/MX6C1%20Manual.pdf?dl=0

https://youtu.be/iNWOVTvoim0

 

[zamproject]

Hello Rob

Welcome here

Hard to say for sure by looking at the video, I expect to see "noise" like hum or hiss, seem more a big pop like if something short the supply rail, or a bad contact in critical area... look like it's linked to mechanical stress.

Best
Zam

 

[mjrippe]

or a bad contact in critical area... look like it's linked to mechanical stress.

Taking this thought further, check all the channel connectors are clean and making good contact.  Examine for dry solder joints.  Do you get noise with no channels installed?  Try the channels one at a time to see if it s single channel that is amiss.  These are fairly simple mixers and they can easily be broken down to smaller components for troubleshooting.  Let us know what you find!

 

[Bo Deadly]

Just divide and conquer. You already have to some extent. It looks to me like the level of noise is controlled entirely by the master section. Also, according to the VU meters, the noise is on both main outs. Can you get any noise at all if the master fader is all the way down? If no, then that would suggest that the noise is not upstream of the master section. It also seems like just grounding the chassis has an effect as well which is telling. If you tap on it with something plastic does the noise still occur? If you lick your finger and very gently touch something on the chassis that has good electrical contact do you get any noise at all? Use a meter to check resistance between the earth pin of the power socket and chassis. What do you get? Use alligator clips to attach meter probes so that you don't have to touch the probes to see the reading. Try tapping / touching again to see if it has an effect on the resistance reading. Try removing things systematically like all input connections, modules like talkback, headphone, etc to see if it has an effect. Just keep going and eliminating things one-by-one. Depending on how old it is, how much abuse it's seen, it is likely to have multiple problems (left led meter goes dim when at max). Get as far as you can and post a new video.

 

[dimesav]

Troops, thanks for all the replies. I had a bit of time today so took the mixer apart and tested what I could.

I tried various combinations of all the modules, also prodded about gently with a pencil while running audio to check components that might be loose etc:

PSU + 8 channels + Aux Module (sound from aux master out) - all working as should, no noise when moved/tapped.

PSU + Master - no noise.

PSU + Any combination of the channels + Master (and after stereo ppm meters) - noisy when moved/tapped.

I had a thorough play about with all the different combinations of the modules and think it might be the card connector on the master. The noise was particularly responding to when the module was pressed or lifted slightly. I had all the modules out and tighted up the bus card a little on the bottom of the mixer, which initially seemed to do the trick but after running a while it soon reappeared. The mixer itself works flawlessly and silently for spells which makes me think its not a component? Any tinkering around the components didn't trigger the noise either.

Squarewave - I tried to get a reading between the earthpin on the power connector and the chassis, hope I'm not being dense but did this while the console was off! Couldn't get into the connection with the plug in as its all insulated up at the innards. Have a hunch you  meant to test while powered up? Anyway.. got a reading of 2ohms from certain points of the chassis, nothing from others.

Also, tapping on it with something plastic/wooden still caused the noise, and the problem seems to be before the master fader as is silent when pulled down.

Should of taken another vid as it might of been more illumatinating but its all back together now. Was wondering if it might be something on the bus card instead of the card connector on the module, not really all that sure but might investigate new connectors.. 25 pin according to the manual.. is this pretty standard? Had a cursory look on farnell and didnt see much.

A final question, the manual states the mixer doesn't have to be earthed as well insulated, is it worth running the external earth on the rear of the mixer to anything to test?

Thanks again,

Rob

 

[radardoug]

On the video it sounded to me like a dry joint. So in the master section near the connector. Visually inspect the board very carefully. Look for dry or bad solder joints.

 

[Bo Deadly]

Squarewave - I tried to get a reading between the earthpin on the power connector and the chassis, hope I'm not being dense but did this while the console was off! Couldn't get into the connection with the plug in as its all insulated up at the innards. Have a hunch you  meant to test while powered up? Anyway.. got a reading of 2ohms from certain points of the chassis, nothing from others.

Resistance measurements must be done with the power off. Otherwise, even small currents can throw off the meter.

In theory, if all of the connections in and out are balanced, connecting the chassis to earth should not impact performance. It is primarily for safety. Perhaps there is something special going on because it can also run on battery. If you don't plan on using battery, you might try to properly earth ground it. If resistance between earth pin and chassis is 2 ohms (not clear that's what you did from your description), that is too much. It should be near zero. Note however that it can be difficult to get your probe tips to get through plating and anodization. So you might start by just testing chassis to chassis until you get a proper zero reading. Also sanity check what "zero" is by connecting probes together. Then, after you've found a good spot on the chassis, check the earth pin again. If it's not zero, you should divide and conquer that and figure out why.

Also, tapping on it with something plastic/wooden still caused the noise, and the problem seems to be before the master fader as is silent when pulled down.

First, my last comment was wr-wr-wrong when I said it would not be upstream if the master down cut out the noise. If the noise goes away when the master is all the way down, then the issue is in the master or upstream. So still divide and conquer but upstream.

A final question, the manual states the mixer doesn't have to be earthed as well insulated, is it worth running the external earth on the rear of the mixer to anything to test?

Again, I actually don't think that's the main problem. It might be an issue. It sort of sounds like maybe something is actually causing the chassis to develop a voltage that gets discharged when you touch it. But that would be a separate issue.

I would say just keep doing what your doing. Try to pull out as much as you can (can channels be removed?) to reduce the possiblities and then just keep trying to narrow it down. It sounds like it's in the buss or master or connectors like you said. If you narrow it down that far, you could just try to connect the meter hands-free as described before and see if the resistance jumps when you tap or press on the backplane. If yes, then it's a simple matter of narrowing the test points incrementally until you find the bad connector or whatever it is.

Definitely could be a bad solder joint like radardoug says. Solder joints can crack and loose contact. They look fine from a distance but there's actually a crack and the two parts are just touching. After a short time (sometimes within minutes) oxides build up and it starts to loose connection. But it is also very possible it could be a bad connector or a burned up resistor of half-a-dozen other things.

Just keep going. Great learning experience. And it's a v. cool peice of gear. I don't own a mixer but I would like that one because it's got bantam jacks on the back and I'm a patchbay / bantam jack fan.

 

[dimesav]

Thought I would put a wee update on this despite it being ages ago, incase anyone else has similar issues. To cut a long story short I got in contact with a tech who happens to stay local to me. He narrowed it down to a bad contact on the edge connector on the master module. After removing it from the bus board and cleaning the pins then resoldering the mixer is working as normal. Must say it feels good to finally have it operational, been haunting me one way or another over the years! I think a few of you suggested a bad joint so right on the money there. There is a slight issue with the led's on the ppm module wigging out a little but only when pushed up into the red, also a spike when its turned on but can live with this for the time being. Thanks for the contributions, now to mix  ;D