Has anyone measured an SC140 to either confirm or deny the 9 dB self noise?
On Sun, Jun 25, 2023 at 12:57?PM Stephanie <
Qwertys@...> wrote:
Thanks for the verification and tips. I attached the updated schematic. I don't have a tool to verify zener diodes yet, so I only saw the forward voltage drop of 0.7v. Looking at getting the cheap GM328a, it seems to be popular over at EEVBLOG.
I pulled the SMD cap values from an old forum post so I haven't checked any yet. I can't find my fancy LCR meter else I'd remove the capacitors and verify. I bought 3 SC140 mics, 1 to take apart and play with so I'll have a working set at all times - so let me know if you need anything else measured.
I plan on 3D printing a replacement nose cone so I don't think PCB thickness will be an issue. Standard PCB thickness is 1.2 to 1.6mm - 1.6 being a bit nicer for structural strength.
I double checked the PCB width in multiple locations and still measured 16.4mm, however that includes the leftover material from the V cut, if I carefully measure the width around it, I get 16.1mm minimum. So taking the difference we get 16.2 to 16.3mm. You can get away with 16.4mm but you might need to file the edges a little due to the kerf.
I also double checked the capsule thread with my thread gauge and can confirm it's 0.5mm pitch. For comparison of 19mm thread capsules, I found a thread that states the Rode NT5 has 0.4mm pitch and the Behringer B5 is 0.45mm pitch - bummer. The ID of the capsule retaining ring thread is 18mm so it's probably 18.5mm*0.4 to 0.5mm - maybe I'll have some luck finding a capsule housing this can go into instead. (I really should learn how to use a lathe and just make this stuff myself).
Speaking of PCB's I have a question for the group. I was thinking about how the body ground is only connected to 1 point - the set screw on the XLR connecter. This means that the return signal path for the capsule must go all the way around the body, through that screw, and up the length of the PCB back to the JFET bias circuitry.
I was wondering if it would be any better to add edge spring contacts to the edge of the PCB to contact the body. This would remove the 200mm+ loop that the ground would have to travel from the capsule. Something like this??edge mounted sideways.
-Stephanie
