NEW!!! SC-1 Mic Preamp Kit
Status: Under Development:

FINISHED!!!!!!!!!

Worked on this project this Friday, Saturday and Sunday.... whew!

Since I used an external 12-pos switch, I basically had to solder 13 wires, so that equals 26 solder points per channel, or 52 solder points for 2 channels!!! I wouldn't recommend this approach. The wires are also prone to RFI pickup. I made the wires as short as I can but still, it's prone to pickup interference.

I would recommend you guys use the onboard PCB selector switch instead.

To fix the RF problem at 66dB and 72dB Gain, I "discovered" a new (new for me at least) of fixing ground loop/rf problems.

I wired the ground of the 1st channel to the XLR output gnd of the 2nd channel and vice versa. That lowered RF problems, but there was still some slight noise but I noticed that if I parallel the 2 gnd wires and stick them flat against the case, it fixed the RF problem. So that's what I did. You can see the "black tape" holding the 2 gnd wires flat against the case.

I don't know what to call this method... It is definitely NOT a star ground. It's more like an X ground.

Now, the only thing you hear is normal "hiss/white noise" at 100% volume @ 72dB gain! There also seem to be a spike at 15.7Khz. But at normal listening volume (unity gain on mixer), the hiss/white noise is only slight even at 72dB.

Some photos!!!

From this....

To this....

Some close-up photos.

Rev3.00 PCB will be coming in middle of this week from the PCB manufacturer, and then I'll test those samples by building prototype #003 and #004.