I need some help with my two DIY KM84 mics:
This is my first build of FET-mics, so I might have missed something.
I have two problems:
Both microphones have a self-resonance (see the spikes in the picture).
One mic has a normal output level (compared to my KM184), the other mic has about 6 dB lower output. They both sound OK (sounds very flat, all the way down. More so than my KM184. The high-end is not as “essy” as the KM184, also as expected).
I have not adjusted the bias yet. I started with R3 at 10k and the self-resonance was very bad. Dropped it to 3.9K, and the self-resonance was better but still there. Same thing for both mics.
And yes, the PCBs are very clean.
Does the self-resonance have to do with the bias adjustment or is it something else?
I’m using the 3U GZT-84 transformers that came with the kit, but I don’t that has anything to do with my problem.