Soundcraft 8000 Master channel noise issue

Founded in 1973, Soundcraft first made its mark with the launch of the Series 1, the first mixing console in a flightcase.

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Soundcraft 8000 Master channel noise issue

Postby Tonealive » Mon Feb 23, 2015 10:08 am

Hi, I recently acquired a 24 channel 8000 to use in my studio. Everything is working pretty well except that there is a really bad buzz/hum the when I bring the main master or aux master faders up, even when nothing is routed to the master (mix) at all and all tracks/groups/fx are off. Changing which outlet the 8000's power supply is plugged into has a significant affect on how much noise comes out of the master main and aux outputs, but even the best option is horrible. I track everything through the channels and then direct out to the converters, and while there is a very small amount of a similar noise on the channels themselves if I really crank them, it is not enough to be a problem at all - very minimal.

But I would like to be able to monitor and sum through the master channels, but there is waaay to much of the buzz/hum.

Does anyone know how to fix this? IF I was pretty sure that the problem was isolated to just the master channel itself, I could send it to Jim Williams or something. But I don't have too much interest in tearing the board apart to try to solve any grounding issues myself, but it's possible..or maybe I would have it serviced.

Any help is much appreciated
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Re: Soundcraft 8000 Master channel noise issue

Postby GJC Designs » Tue Feb 24, 2015 2:01 am

You have said that connecting the desk PSU to different power outlets makes a big change in the noise. This is a pointer to a power & grounding problem. Until this is investigated thoroughly, fixed, and proven to work, anything else is a waste of time and effort. You need a good, solid point from which to start. Within reason, it should not matter which power outlet the console is plugged into.
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Re: Soundcraft 8000 Master channel noise issue

Postby Tonealive » Tue Feb 24, 2015 7:19 am

Hi Gareth, thanks so much for responding. Note though that all my other studio gear is plugged into the same outlets without having an issue. I should be able to put the master fader up to unity gain and hear maybe a comparable amount of noise, instead it's very abnormally loud even plugged into the same outlet the other gear is plugged in. I'm not sure that I can get the power and grounding improved too much. The outlet running the studio gear is already own circuit coming from the board. What else can I do?
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Re: Soundcraft 8000 Master channel noise issue

Postby GJC Designs » Wed Feb 25, 2015 2:17 am

There are some checks that can be easily done to point towards if it is the console or some other influence. Remote diagnosis of faults over "N" thousand miles is always a challenge :)

At this point, based on your description of the noise being a bad buzz/hum, I'm primarily suspicous about wiring and grounding, both mains power and audio. Especially if hum is the predominant noise. Also, especially as moving the console PSU from one mains outlet to another has a significant effect on the amount of noise.

If buzz is the predominant noise, then it could be a console PSU fault; maybe a faulty voltage regulator or a bridge rectifier that has failed. Without getting too deeply into circuit diagnosis, some basic system connecting can help a lot in providing pointers.

Please make sure that there are only 3 cables connecting to the desk for this check - console PSU cable and the monitor left & right output cables. With only your monitors and console powered up, and only the monitor output lines from the console to the monitors connected, do the monitors hum or buzz or are pleasantly silent (with a little hiss), as would be normal for a console & monitors only?
From memory, there should be an earth bonding screw on the master rear connector panel, so if there is still hum/buzz, try running a thick grounding wire from the bonding screw to a known to be good ground at a mains power outlet. What is the hum/buzz situation now?
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Re: Soundcraft 8000 Master channel noise issue

Postby Jim Williams » Wed Feb 25, 2015 10:46 am

Disconnect everything from the console except for headphones and a mic/cable. Then check for noises. Many converters spit out noise, best to eliminate any outside interference when testing for noise.
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Re: Soundcraft 8000 Master channel noise issue

Postby Tonealive » Tue Mar 03, 2015 3:27 pm

Ok, I disconnected everything except for the monitor outs and power chord, ran some tests, reconnected, and done a few sessions since. For the most part, total success! Here is what was going on. When plugged into other outlets, the noise is worse no matter what. However, when 1/4" cables were plugged into any line in on the console, it dramatically increased the amount of buzz/hum whether the channel was on and routed anywhere or not.

But, when plugged into the studio outlet (that's on its own circuit) this problem with the connected 1/4" cables does not occur, and the noise on the master fader is better in general.

A little adjustment to the gain staging with the amps and crossover, and I have a pretty noise free system!

When the master is cranked, I still hear a little buzz/hum, but it's minimal and not a problem. But it's still there a tiny bit, and that issue with the line ins when the console is plugged into other outlets seems to point to a potential problem with the power in the house in general and with the console.
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Re: Soundcraft 8000 Master channel noise issue

Postby Tonealive » Wed Mar 11, 2015 1:07 am

Hey Gareth and Jim, I'm having a new problem that has come up in the last few weeks, completely not related to the buzz/hum that was pretty much solved.

Right when I power the board on, the right master channel (in both the main and aux masters) plays everything coming through it fine, but the left master channel is very low in output and staticy. The static seems to get louder and louder until after about 20 minutes, it pops, and after that, everything is fine; static gone, good clean signal coming through. It seems to be taking longer and longer for the channel to "pop in". This problem occurs when playing a signal through the master from both the cassette in as well as a signal coming in through the channels. Also, when pressing the mono button on the Aux master fader, the signal coming from the left speaker is then normal... so it seems to be a problem somewhere in the input path of the master channel. Is this a cap that needs replacing?
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Re: Soundcraft 8000 Master channel noise issue

Postby Jim Williams » Wed Mar 11, 2015 9:52 am

Check the insert jacks.
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Re: Soundcraft 8000 Master channel noise issue

Postby Tonealive » Wed Mar 11, 2015 1:30 pm

Thanks Jim, I just tried that. unfortunately, still same issue. I put isopropyl alcohol on a 1/4" plug and worked it in and out of each of the master insert jacks a few times.
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Re: Soundcraft 8000 Master channel noise issue

Postby jensenmann » Thu Mar 12, 2015 1:41 am

You won´t be able to clean the contacts of the insert switches inside their jacks that way, unfortunately. If the desk has unbal. single-jack inserts then use a TRS jack and bridge tip to ring. If you insert this plug it will open the internal switches but still shorten send to return. If the desk has seperate send and return jacks the simply use a balanced TRS cable to connect send to return externally.
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