[TzeYang]

Okay I was helping a friend fix his PPA V2 + STEPS (all-in-one case)

I've observed some ringing noise especially if the volume pot is turned up.

Because of the size constraint the Amveco Toroidal is just next to the input.

Opamps used are OPA637 (Gain of 11)
Ground Opamp = AD829 with compensation pin as output

L/R Opamps Class A Biased

I've tried grounding the RK27 but it seems that this is not the problem.

Any suggestions?

 

[tangent]

What is plugged into the inputs of the amp? To test self-noise, you should plug shorting plugs into the inputs, so they're grounded. If the inputs aren't connected to anything, the noise could be interference coupling into the inputs. If there is a source plugged in, you could be hearing noise generated within the source. This latter is fairly likely given the high gain.

If the noise is still there, try disconnecting the STEPS from the PPA and power the amp from another source. If the two are hard-wired together, now is a good opportunity to add a connector between the two. If the noise doesn't go away, it isn't the STEPS. (I rather doubt it is, since noise from the STEPS should be a low hum, not high-pitched.)