I took some time to try to reverse engineer the tBone SC140 PCB. The board itself has 797 Audio printed on it, so there's no doubt as to who makes the mic.
I had searched for the original schematic and couldn't find the one by Khron, but I found a post that listed the Cap values. They seemed to match so I filled them in, however I haven't verified them yet.
I have double checked my work the best that I could, though it's very possible that mistakes exist.
I took measurements of the PCB and the housing, and got the following dimensions:
PCB is 16.4 by 107mm and 1mm thick
Bottom of PCB is 6.5mm from the OD of tube, or 1.25mm offset from the center.
Body Tube ID is 17.5mm
The body capsule threads are 19mm diameter, 2mm long and 0.5mm pitch
The body is 20mm diameter and 132mm long (without the capsule installed) 146mm with capsule.
Capsule pogo pin is 2.5mm diameter, 17mm long, with 3mm travel minimum (I'm not having any luck finding suitable replacement pogo pins)
The capsule pin is inset 3mm.
The switches are 61mm and 81mm centered from the XLR connector side of the PCB
The vent plate on the back of the capsule is the common 8 hole type, looks cast but is really high quality with straight holes and very flat.
Q1, Q3, and D4 appear to be made by Galaxy Microelectronics, and the JFET Q2 by Fairchild.
D3 and D1 have 0F marking on tip, with a sideways J.
It is assumed that the capsule is biased with a negative voltage.
It's an interesting design and I'm trying to understand how it works.
I don't have a test setup to check the voltages yet. I'm looking for a high impedance multimeter or circuit that I can use.
-Stephanie
