Do I have adequate crosstalk and ground loop preventions in place?
As a kid, I built numerous multi-stage bipolar AC-coupled low-frequency amplifiers..................that oscillated. Eventually, I learned to avoid that fun putt-putt-putt-putt of motorboating oscillators (caused by the shared internal impedance of 9 volt batteries); the key concept is "local batteries", achieved with R_C_R_C_R_C_R_C networks to isolate the high frequency current surges.

Imagine a circuit with 10 amplifiers, and 10 bypass capacitors, each capacitor installed 1mm (one millimeter) away from the VDD pin of each amplifier.

Run a heavy wide VDD trace all over the board. And have a GND plane underneath.

What happens? Any current demand by any of the amplifiers will cause a VDD sag all over the PCB within a few nanoseconds. This sharing of the VDD is the path to oscillation, and to trashed video/audio circuits.  

How to prevent this sharing, this upset of settling to final values, this potential oscillation? Use some isolating resistors. 

FORM A VDD TREE.

Using this concept, I build a rather broadband amplifier, gain of 600,000 or 116 dB, Flow of 50KHz and Fupper of 200KHz. There was no oscillation.







simulate this circuit &ndash; Schematic created using CircuitLab

There will be DC interactions in the GROUND plane. This particular amplifier was quite high passband --- 50Khz to 200KHz --- and with at least one DC_block RC in each stage, the DC-feedback by GND PLANE was seeing 4+ zeros (anti-pole) of attenuation.