Soundcraft 200b

[iprovlek]

Hi guys!

Have problem!I bought OPA2134 and put in place Tl072,i solder 100nF ceramic caps V-,V+ to GND, but still have a big oscilation

on strip module of my Soundcraft!

I dont no what to do!?

Please help me...

 

[sahib]

This is avery common trap that every so often people fall into.  There should already be a thread about it.

However, Gareth Connor who is the designer of that console is a member and he may give the best advice.

 

[jensenmann]

That´s not enough information for troubleshooting.
First and most important one: never listen to advice posted at gearslutz

Do you have oscillation when you use a) mike input b) line input c) both?
Does plugging in an unused insert cable interrupt the oscillation?
Is oscillation audible in a) master out b) CTRLroom out c) group out d) direct out e) aux pre fader out f) aux post fader out or any combination (which one?) of these?
Does the level of oscillation follow any fader/knob position? Which one?
Is oscillation audible when the EQ is in/out?
What frequency is the oscillation? Or is it noise?
Is your oscillator switched off?
Did you check the PCB for solder blobs/shorts/broken traces/unsoldered parts/cold solderjoints?
Did you try to put the original TL072 back in your suspect channel? Does it work with these? (try to exchange one chip after another and check after each change what happens)

keep us updated

oh, btw, if you changed all TL072 to OPA2134 your PSU is loaded like hell. Better get a beefier PSU.

 

[iprovlek]

Thanks guys!

I learn this now "never listen to advice posted at gearslutz"!

My peak red lamp is on all the time even if microphone isnt plugeed in mixer....

And oscillation is audible on CTRLroom, Master everything...

Check all solder joints every thing is ok...

When i return Tl072 in place of OPA2134 evrything is ok,and work very well....

I put better an bigger caps in PSU and PSU its all repaired....

 

[MagnetoSound]

I suspect that the regulators in the PSU may be oscillating under the extra load. Even renewing and upgrading the output caps may not be enough to prevent this.

I have found that locally decoupling the regulator outputs to the ground pin (or the adjust pin on an adjustable regulator) can fix it. The negative regs are particularly prone to oscillation even under normal load. Try a 1 or 2 uF directly from the output pin to the adjustment pin and it might go away (pay attention to polarity, obviously).

Having said that, of course if your op-amps are drawing more than the regs can manage then all bets are off. 

 

[Andy Peters]

I learn this now "never listen to advice posted at gearslutz"!

That's the best advice of all!

-a

 

[iprovlek]

Thanks Magnetosound...

And yes Andy that is true....

I think that i find the issue of my problem!In orginal PCB of my Soundcraft channel strip, C8 and C11 ceramic caps are moved!

And this two caps goes straight over first IC's,its 33pF ceramic caps!So i think that cause ground loop,cause red peak lamp is lighting all the time!

So this cause audible distortion and oscillation....


Thans guys again...

 

[iprovlek]

And all thanks to Living Sounds....

He solved my problem....