Mixers/Consoles Mackie SR 24-4 noise issues

[Aman121]

Hello CB

Our Mackie SR 24-4 has started outputing a humming noise on both the mains and all the aux sends. The noise is not effected by the position of the master or channnel faders, and I am sure the trouble is with the board, as the rest of the system worked fine when we swapped it out for a rented unit. The board is probably around 15 years old, and unfortunatly replacement/proffesional repair is not an option until it catches on fire or accidentally has a cinderblock dropped on it .
So do any of you have any thoughts on dealing with the noise? If it is something like replacing filter capacitors, I might be able to handle that; I have done audio repairs before.

Thanks, Andrew

 

[venuetech]

A common Cinderblock only weighs about 40 lbs, I would suggest using a filled block. (75 lbs)

No hold on.. someone is likely to have a better answer.

 

[Lambda]

Seeing as how the noise seems to be ubiquitous on your mixer, I'd guess it's a problem with the power supply, likely the filter capacitors.
The power supply schematic is available here: mackie sr24-4 Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics (Its file name is power_51A) It also has there a visual layout of the circuit.
Judging by what you've described, I'd guess that either c1, c2, c3, c4, c10, or c11 has failed, introducing ripple into the +/- supply for the mixer's op-amps.
Good luck with that repair. While you're in there, you may want to replace the ribbon cables. These cables can cause problems on some Mackie consoles when they get to be as old as yours.

 

[chausman]

If you know it is the board, then start with everything unplugged and turned down (eq at 12 o'clock). Do you still have noise? If not, start adding things like effects and certain mics back into the mix and see when the noise comes back.

(If there is noise with just the console alone, then you can ignore this.)

 

[bishopthomas]

Also, opening the hood on one of these bad boys is no cake walk. I'm inclined to go with the cinder block idea. Or you could put it to use as a door stop, boat anchor, paper weight, or other cliche useless items.

 

[Footer]

I have never met an SR 24 that did not have noise issues. You can do the poor mans repair and re-cap it as others have suggested and that might help. The fact that it has survived for this long is really something. Most of the SR 24's that I touched 8? years ago were falling apart.

Buy a GL2400, for 2k you get a good console that will last.

 

[Aman121]

I have never met an SR 24 that did not have noise issues. You can do the poor mans repair and re-cap it as others have suggested and that might help. The fact that it has survived for this long is really something. Most of the SR 24's that I touched 8? years ago were falling apart.

I dont have pictures, but the console has survived everything from soda spills to 5 ft drops. It looks like its been through a tornado. (probably has)

Thanks everyone for your input. I will see if I can crack the thing open and replace the power supply caps. I will also start making noises abvout a new console, and plan to visit the local masonry supply center just in case all else fails.

 

[FMEng]

The problem is almost certainly failing electrolytic capacitors on the two analog rails of the power supply board. Those are C1, C2, C3, and C4. While there, I would also hit C5, C6, C7, C8, and C9. The parts may run $25. Digi-Key, Mouser, Newark Electronics are all good sources for those parts.

This isn't a Mackie problem. This is a common problem for any equipment that runs warm by design or is exposed to heat long term. Power supplies run warm, while the audio sections don't, which is why the supply is usually the where the failures occur. Heat dries out the chemicals in the electrolytics and they die. Other types of capacitors, typically smaller values, are fairly immune to heat. Electrolytics are usually the ones bigger than 1 uF on up to 10,000 uF, or so. Most of the time, they are polarized, so pay attention to any - or + markings on old ones and the replacements.

 

[Clifford]

In defense of the Mackie's, our 32-8 is still going fine. A while back our district went with new boards (literally, "a round of Mackie 32-8s for my friends!") and so far the power supplies have been more trouble than any of the boards as far as I've heard. That said, ours is the only one left...

 

[Aman121]

Just wanted to report back for any future thread viewers that the fix worked great, for better or for worse the mixer is back in service and is almost dead quiet now.