Just a quick doodle in Paint with some thoughts.
- flip the trimmer 180deg and shift it to the right
- swap the placements of those two electrolytics, so you can then route those two traces under the transformer coupling cap (as opposed to "outside" it)
- that being said, you'd rather want those caps closer to the series resistors they're connected to (ie. on the other side of the board), but considering the minuscule currents involved, that may well not be an issue; just another "best practices" type thing
- why run traces so close to unrelated pads though, why route them so close to edges (like the transformer cutout), and/or why come off pads at an angle, if not necessary?
- also, since you're not exactly starving for board space, why not use thicker traces? Those look unjustifiedly thin, and it kinda freaks me out, especially when they're routed so close to things...
Thanks for all the thoughtful tips
@Khron . I will definitely look at each of those points moving forward.
I’ve confirmed that everything in rev 1 is working. Next rev will have updates like proper mounting hole placement, better track routing and thicker tracks. I also think I want to swap out the trimmer for a right angle one so I can turn it without taking the bottom bell off. Also thinking about incorporating a pad switch with the 15pf feedback between the polarization line and the drain. ( like on the original schema ).
I ditched the dc-dc using matadors board design because the parts were just too massive for this build. But I’m thinking for the next one I want to look at the u87ai daughter board and make something like that with all small smd parts. About the size of a us quarter coin
. That will give me more output… even though ruud pointed out it would only be a few db, I want to take on the challenge.
LOL sorry for freaking you out with my tiny traces.
I got my cm5722 transformer in the mail and put the whole revision together. It took me a while to realize that I had to turn the fet source resistor to get the fet to start doing its thing and pass audio ... *facepalm*
After this discovery it would pass audio reliably. I tried to follow the fet bias procedure. I injected signal into gate from daw and tried to get the clipping even and such. I had no idea really what was the correct way. I attempted to balance the distortion on top and bottom with test signal. However, after this procedure it would not pass audio from the capsule so I obviously did not do it correctly… this is my first fet mic project. Still getting my tool belt in order.
Also, please excuse the slight singe on the film caps. Woopsie.
Can anyone help point me In the right direction beyond what I learned in this post?
(
Mic Biasing )
When trying to bias the fet, I was using the daw signal generator and an oscilloscope plugin. Is there anything I need to do to condition the signal to interact with the fet? Such as passing through a high value resistor or anything? Just measure the output voltage of the daw signal? Do I feed the signal straight into the gate? Or do I feed it where the capsule signal is fed? I was feeding it directly to the gate.
Any tips would be so helpful for dialing in the fet bias …
Cheers!
PS. No pictures of the installed board yet: forgot to take those before I went on this LA work trip.