Biasing FET Condensers - Shielding and 60hz hum

[Scrappersa]

In my KM84/U87 circuit, I've been trying to use the oscilloscope method for biasing- biasing for symmetry on both sides of the waveform.

When using this method, the electronics have to be outside of the body so I can adjust the trimpot. The issue I'm experiencing is that the 60hz cycle hum is so significant that it is obstructing the waveform and I'm not able to accurately bias it.

How do you all handle this when you bias your mics?

 

[Khron]

Plug your mic into your interface and use REW's RTA function?

 

[Scrappersa]

I thought that the issue with plugging into an interface is that it takes out the DC which won't give an accurate reading.

Also, my understanding is that most people bias using an oscilliscope which I have access to. Either way, it being outside of the body is causing massive amounts of 60hz hum which is getting in the way of allowing me to bias it.

 

[kingkorg]

I inject the signal directly to the gate of the fet, that souldn't give you any hum.

 

[Scrappersa]

Works perfectly. Thank you!