Can someone pls check my power filtering

[ftumch]

Think this okay but a second opinion would be nice as there's some guess work on my part

I've got a very squeal-y circuit and I want to isolate the transistor section (VA) from the op amp section (VB and VR)

R1 = 100r
R2 = 33r
R3 and R4 are 10k for VREF voltage divider

There's pads under the ICs for extra 100n MLCCs if needed

Is this how it's done?

 

[NickKUK]

Do you know what frequency is causing the feedback? How much current?

Problem with RC filters is that you loose voltage headroom. Inductors can work well, as too can LDOs like the LT3042.

 

[ftumch]

Do you know what frequency is causing the feedback? How much current?

Problem with RC filters is that you loose voltage headroom. Inductors can work well, as too can LDOs like the LT3042.

It is a specific frequency, with more than one PSU but not an isolated one. I'll measure the frequency when I'm home.

Did a build on someone else's PCB and they only spec'd a single 47u for filtering so I want to make my own PCB

 

[NickKUK]

The other option is to add bypass caps to the power pins so any current loop between the opamp power and ground pins is kept as small as possible through the local bypass cap, adding an inductor on that power with a cap at the other side means a CLC filter.

The LDO (low drop out) means a little drop and the LT3042 has a 90dB PSRR happily in the audio range - the effect is it would neutralise that noise on the power rail.

However let's see what we actually have causing the problem.

 

[Stickman393]

Boy howdy that's a pricy little component.

 

[ftumch]

Yeah it is

I'll breadboard the above and measure the voltage drop, it might be okay. I can use 220u cap for the op amps

Or use a charge pump and give the op amps 18v and something else for the transistors

 

[NickKUK]

Boy howdy that's a pricy little component.

317 - old school,
3080 - 70-80dB PSRR up to 1.1A, parallel/chainable
3042 - 90dB PSRR but up to 200mA, parallel/chainable

Just be a little careful with the ordering of the packages, these 3042 which should be good for pedals etc but need some PCBs made up:

 

[jwin615]

Another option is a dual out isolated dc converter and run the opamp stage on +/-5v. Probably make up for the space with lower capacitor count.
Runa separate ground plane and star ground all at 9v input.