Soundcraft Ghost Post Mod Issues

[Aniol1349]

Hello guys!

I have recently finished modifying a whole Soundcraft Ghost console and I'm left with four issues.
The console was fully recapped increasing all the coupling caps to 220uF 25V.


1. The Line level gain pot when goes past 90%~ starts to create a massive amount of noise. The op amp for this section was changed from the original TL072 to BB OP2134. I have added 0.1uf ceramics parallel to the voltage divider of this op amp.

2. Mix B send on 4 channel modules introduces some kind of frequency sweeps noise with pops. The Mix B op amp was changed from 5532 to AD OPA275. I have also taken feed from this op amp for my afl metering mod. The feed was taken pin 1 and fed into the R19 which normally takes the tape signal to the meter.(marked on the schematics)

3. I have some amount of DC on the faders making them slightly scratchy. I have increased the fader caps from 2.2uf 50V to 10uf 50V. This problem is present on most of the faders in the console.

4. Several Tape trim pots make really loud noises and scratches. They have been cleaned several times with servisol super 10 cleaner.

I would appreciate any tips/comments on how to look for solutions to these problems.
For reference I'm attaching a copy of the schematics.

 

[moamps]

1. The Line level gain pot when goes past 90%~ starts to create a massive amount of noise. The op amp for this section was changed from the original TL072 to BB OP2134. I have added 0.1uf ceramics parallel to the voltage divider of this op amp.

It looks to me that your opamp start to oscillate at high gain. Where did you exactly add capacitors; between power pins and ground?

2. Mix B send on 4 channel modules introduces some kind of frequency sweeps noise with pops. The Mix B op amp was changed from 5532 to AD OPA275. I have also taken feed from this op amp for my afl metering mod. The feed was taken pin 1 and fed into the R19 which normally takes the tape signal to the meter.(marked on the schematics)

Same here.  Be sure that R19 is disconnected from tape in opamp. Also you can add here capacitors from power pins to ground.

3. I have some amount of DC on the faders making them slightly scratchy. I have increased the fader caps from 2.2uf 50V to 10uf 50V. This problem is present on most of the faders in the console.

You shouldn't have any DC on the faders. Test it using DVM. If the faders are noisy, you should clean them. Take them apart and clean the graphite surface and sliders with water and Q tips. 

4. Several Tape trim pots make really loud noises and scratches. They have been cleaned several times with servisol super 10 cleaner.

Obviously cleaning dosn't help any more, so you should replace them.

 

[Aniol1349]

I have placed bypass capacitors parallel to the voltage divider R12/R13, from power pins to ground and I have also placed15pf small smd caps between the pins 1/2 and 6/7.

I have also tried leaving out the last smd caps and not much changed.

the problem still remains on high gain.

 

[moamps]

You should place decoupling capacitors directly from opamp's pins 4 and 8 to ground.  You don't need capacitors on R12 and R13.