Wierd mixer problem..

[Optical]

I have a faiirly cheap mixing desk, full of opamps..

The problem is the left side of the master channel cuts out completely when the level is low.. When the level is increased to around 0dB theres a slight popping sound and the channel springs back to life..

so basically i have to keep my master level high or it cuts out..
It seems to be soley electronic as opposed to a mechanical fault..

has anyone heard of opamps cutting out at low levels?

 

[pinkmouse]

Sounds like a faulty volume pot to me. Give it a blast with some contact cleaner, or swap it out.

 

[Optical]

Well im pretty sure its not mechanical as it is completely unrelated to where the fader position is..
But i'll give it a go, nothing to lose..

 

[Netlist]

Bad solderings?
What brand and type is it?

/Hugo

 

[Optical]

heh, Its behringer..
If the output level stays above 0dB it always works fine..
could be a dry solder joint, but you'd expect it to cut in and out when you jiggled things..

faulty cap perhaps? I really have no idea.. its got me stumped..

 

[Netlist]

when you jiggled things..

Yes, in many cases you are correct but a thorough checking will rule this out.
I usually inject a sine wave in one of the inputs and try to follow the signal path with a scope.
I could be a faulty cap but this is about the last thing I would look for.

/Hugo

 

[pinkmouse]

I could be a faulty cap but this is about the last thing I would look for.

I agree, my money is still on the pot. Those sypmtoms sound exactly like something liquid has been spilt over the mixer.

al/ remembers a Janet Jackson gig where a 2 litre carton of orange juice sailed majestically out of the crowd and landed right on the 48 channel Amek monitor desk.

 

[Frank Berry]

What Behringer model?
Does it use VCA's for faders?

 

[Centauri]

heh, Its behringer..
If the output level stays above 0dB it always works fine..
could be a dry solder joint, but you'd expect it to cut in and out when you jiggled things..

faulty cap perhaps? I really have no idea.. its got me stumped..

Can tell you exactly what it is - ribbon cable from mainboard to output jack board. The cable conductors are too small for the IDC connectors - replace cable with some decent stuff.

Very common - other ribbons quite oftencause channels to drop out.

Cheers
Graeme

 

[Optical]

Im not quite sure what you mean by the ribbon cable being too small and causing the drop-out.. you mean physically too small? or electrically?

ok, well i guess i'll be pulling it all apart then.. the scrutinising with the scope thing is what i was planning on, not particularly looking foward to it though..

oh, it's an MX1604 for those interested. its never had anything split on it, does get a little dusty and the cat is always around

 

[Centauri]

If you prod the ribbon, fault will probably come and go. The conductors in the ribbon they use is a lot smaller diameter than standard computer ribbons, so there is not enough pressure from the knife edges in the IDC connectors to be reliable.

Cheers
Graeme

 

[Optical]

Interesting, so why would the audio voltage source level change the connectivity?

 

[Centauri]

This is a common symptom of a loose connection - if there is high resistance, when you increase the level at some point there will be enough for the signal to "break through", and when signal current flows the resistance of the connection drops. Dirty switching contacts on insert jacks will behave the same way. With the Behringers, all controls are mounted on the circuit board, and not the front panel, so movement of controls can even vibrate the board enough for a loose connection to play up.

Cheers
Graeme

 

[Optical]

I see, thanks for your input!
I'll let you know how i get on

 

[Enzo]

You beat me to it, I was going to also suggest the insert jacks if it was not the ribbon described. Inserts and effects returns are very common problems with the exact symptom you describe. On all brands.