Soundcraft K2 channels "gating"

[dosxuk]

Some of the channels on our K2 have developed a strange fault - if there is a low signal coming in, no signal will get past the input stage. However, if there is a peak, the channel will suddenly start working again, and then shortly after, start getting quieter again until it goes silent. Another peak will get it going again, exactly like a gate with a very long release. I've been working around this fault by running the channels hotter than I would prefer, and then having the channel faders / aux sends lower (which then causes issues when channels can start peaking).

 

This is happening with both mic and line inputs, with no inserts connected up. It started out just on one mic input, but has slowly spread to others (random across the desk, but the same ones all the time), as well as now affecting the line inputs as well. As all the other features of the desk are working, we're guessing it's a problem limited to just the input stages of the channels.

 

The desk is old (12 years I believe), but was completely serviced by Soundcraft in 05, and has only seen light use since then (around 30 times a year).

 

Has anyone seen a similar fault, and does anyone know if it's something we can fix in house, if it's something it would need to be sent back to Soundcraft for, or if it's time to replace the desk (however there are no funds to do this).

[Simon Lewis]

Surface oxidation of jack or XLR contacts? Try plugging stuff in to inputs and outputs slghtly aggressively a dozen times, including any insert jacks (a classic place to lose signal).

[Bobbsy]

Not specific to a mixer but I've seen exactly this problem due to oxidation in an audio jackfield. I suspect Simon may be on the right track.

 

For the jackfield, we could buy "burnishing tools" in the shape of a GPO jack...I've never encountered one for XLR but it might be worth a search.

 

Bob

[Sound Man]

While using a CD player or something like that connected to the mic input via a DI box try plugging a stereo jack plug with the Tip and Ring connections joined together into the channels's Insert jack socket to see if this solves the problem.

 

If it does, you'll know that fault is with the Insert sockets.

 

David

[dosxuk]

Cheers for the help, we'll get the desk out tomorrow and have a look at cleaning the sockets on the most affected channel and see if it solves the problem.

[Rob_Beech]

I'd be following Simon's route. But maybe not on the input connectors, could well be on something internal.

 

It's not as rare as you may think. A higher voltage present causes things to start working suddenly but then over time this goes again. I'd be thinking about having this in for a service again on principle, 5 years is a fair time, especially with only 2 or 3 gigs a month it gives things time to break. Often, lack of use can be worse than lots of use.

 

 

Rob

[StevieR]

I once had a similar issue on an LX7 on the Aux outputs so I think this may be the same issue. If the connector cleaning doesn't help then perhaps look for dry joints on the PCB. I had dry joint problems on a K1 desk we used to have.

 

Steve

[boswell]

Take the bottom off and reseat all the flexible ribbon cables, with moving the desk in & out of storage they tend to slide out.

I sent our K2 back to Soundcraft for service a couple of years ago and when it came back via carrier (on a pallet) we had numerous faults with it. reseated the ribbons, put it in its final position and no problems since.

[SPTTRIAL]

I have had this problem too on both soundcraft and old DDA consoles, the jack plug socket contact on the insert is normalised when there is no jack in it so any amount of jack cleaning will not make any differeance to the contacts, as a test on a channel that is def faulty, solder the contacts together and see what you get, then if thats it, then you will have to change all of the insert sockets. hope this helps

[mackerr]

I have had this problem too on both soundcraft and old DDA consoles, the jack plug socket contact on the insert is normalised when there is no jack in it so any amount of jack cleaning will not make any differeance to the contacts, as a test on a channel that is def faulty, solder the contacts together and see what you get, then if thats it, then you will have to change all of the insert sockets. hope this helps

It would probably be easier to wire tip and ring together on a TRS plug and insert that into the suspect normalled jack. You can then use it to test other channels.

 

It is also possible to clean the contacts on the normalling switch with a burnishing tool unless it is an enclosed jack.

 

Mac

[j rayner]

I am having this problem whith a k2.on some channels I plug in a mike and get a poor distorted signal.if I put in the phantom power then take it out again the signal becomes good.anny ideas folks

[david.elsbury]

Anny [sic] ideas? Have you read the rest of the topic, there's a few good suggestions in there... check the insert jack, send it to service...

 

Also it might be a dry joint inside on the channel strip, this would require someone competent to open it up and see what's going on.

 

David

[durian]

I had a similar problem on my A&H desk.

 

it was a combination of oxidised TRS and also the gain pots

 

give the gain pots on the faders a good wiggle, if that makes a difference they may be dried up and dusty inside.

 

(as well as the other advice here about oxidised TRS)

[j rayner]

thanks for the tips.I have put cleaning spray on the inserts etc and done the jack thing.all seems well now so fingers crossed.the reason for my poste david was the phantom power thing but I now realise that putting phantom power on may enduce a better contact where contact was poore