Amek Angela -Loss of High Frequencies at Master channel

[smilan]

Hi,
I've finished to recap my console, everything works great as far as frequency response except the master channel.
There's a loss of high frequencies in both channels after the "Buss Amp" (U12 and U14 on the schematic)

This is how it looks at "Insert point 75" (before the "Buss Amp):

And this is how it looks at the output of the "Buss Amp" (leg 6 of U12):

And this is how it looks at the main output:

Since this issue occurs on both channel I'm assuming it's bad design on this stage instead of a faulty component(s).
There's a way to modify some components at this stage and get rid of this low pass filter?

 

[radardoug]

Did you measure response before you started changing caps? It could be something you have done. Find the Angela spec sheet. Its very unlikely that it was designed to be 4 dB down at 16k. Perhaps you have put in a wrong value?

 

[smilan]

Yes, this is how it looks before recaping the console:

The loss at the high frequencies seems to be the same (it's only the graph scale changed from 30 to 16db).
As you can see the response of the bass frequencies has improved while the loss at the high frequencies remains the same.
I've kept the same capacitors rating (100uF /10V) for C 63 and C65 (and C71 and C74 on the right channel).

 

[abbey road d enfer]

At what level have you done the measurement? Maybe the opamp is in slew-rate limiting...?
Have you changed the compensation capacitor (10pF)?

 

[zzjochen]

Hello,
how did you fix the fault ?

 

[zzjochen]

I’ve also an Angela blue 32, and after some mods e.g. changed some leds to blink-led (a full recap in 2014) I loosed nearly the full signal on the right sight of the A32 masterchannel and I don’t know how to fix the problem, so your help would be very greatful
Thank you in advance

 

[smilan]

Hi, do you have any signal on the right master channel?
Do you have the extension card and a scope / audio signal tracer?