Fender Acoustasonic 30 DSP with very audible Hiss

[pa911]

DSP board on Stage 100 and Acoustasonic are identical except for an amp specific programmable U4.

Stage 100:
TP 26 (input to DSP) is about 50% ampliltude of Acoustasonic TP33.
Noise is present at TP27 (output of DSP)but is about 60% lower than Acoustasonic R53 and looks to be of higher frequency. Signal output looks to be 3 times higher.
Noise mostly gone at TP28 (after first op amp stage).

So it looks like the noise may be inherent to the DSP stage and may be the result of U4 programming. i.e. Not much can be done about it.
So I am thinking about possibly reducing the relative noise level of the entire amp by reducing the gain set for U10-A by increasing R53 and R54. This will reduce the effects overall which might be a good thing. I am not sure if this will change the filter network.
Any thoughts out there? What resistances would be reasonable?

[pa911]

Hello
Thought I would give closure to this post.
Decided to look again at this amp. Since noise seemed to start at the U10 stage, I decided to test all components of this stage. Eventually found a near short at R66 - 47ohms in the multiplexer stage. This caused abnormal gain for the DSP signal. Replaced with 18kohms and the amp is now quiet and very usuable. What looked like noise on the scope was the DSP signal.

[g1]

Hello
Eventually found a near short at R66 - 47ohms in the multiplexer stage. This caused abnormal gain for the DSP signal. Replaced with 18kohms and the amp is now quiet and very usuable.

Was the part color coded as a 47 ohm?
Here is a funny story for you. The only time I clearly recall finding a wrong value resistor stuffed in a board was also an Acoustasonic, some 24 or so years ago. And I was working right near you in Surrey at the time.

[pa911]

Yes, color coded as 47 and soldering suggests it was original.