Model 705 Microphone Gain Mod

From the Ten-Tec Reflector December 21, 2000

I made some changes in mine. It was done in an effort to solve, what I thought was an RF problem, but in doing so, I found that I got better audio reports.

Change R1 from 100K to 68K. Change C4 from 220pf to 330pf.

This does reduce the gain of the mic pre-amp stage and maintains the same frequency compensation. The result is that the input to the 1st stage of the Omni VI+ is reduced and (it was my determination) that the front end audio clipping was eliminated. After the modification, the Omni mic level control must be advanced to about the 10 to 11 o'clock position. (Normally it runs about 9 o'clock) The mic level control is electrically located between the 1st and 2nd stages.

73
Bob K4TAX