OK, have some stuff here. Actually at home on a moday with more time than to just get laundry done and head out!
Maybe this will help. The TX provide either a gain of 1 or 3 depending whether it is in the line or mic position respectively. The two gain stages follow the standard gain equation for such stage. In this case it is:
Note:this is for the mic positions only, other things happen in some line positions, see below.
Av=5K1/Req where Req for the first stage is R3//Rswitch(1). Rswitch being the cummulative resitance added by those resistors. R3 is 330K.
Note // = parallel
for the secong stage it is R11//Rswitch(2) where R11=8K2.
The attenuation network provides a 5db range from approx(all this is approx, I did roundings roughly) -1.6db to -6.45db when the wiper is in the middle it is about -4db.
The equation for the att (note: this is ignoring R6 the adjust on test resistor, it is not in place in the unit I have.. more on that in a minute)
Rpt=top of pot, Rpb=bottom of pot.
Att=(R9+(Rpb//R7)) / ((R5+Rpt)+(R9+(Rpb//R7)))
Looking at the values as if the gain was in the -30 position. I'll assume they want to o/p to be 0 therfore a gain of 30db was desired.
So Req for Gain stage = 330K//550 = 549, then the gain is 5K1/549+1 or about 10.29
Req for stage 2 = 8K2//open = 8K2, then the gain is 5K1/8K2+1 or about 1.62
With the att. in the '0' db position or techincally -4db or roughly *.62 then we have
TX * Av1 * Att * Av2 = 3*10.29*.62*1.62 = 31
A gain of 31 is approx 29.9 db, so pretty close to 30.
I believe this to be correct, but I don't do this for a living any more.
The gain works out to the expected value. Next I will layout the gain as selected by the according resistors allowing us the set up whatever gain settings we want and still use the ratio of gain from Av1 and Av2. Coming soo. Promise.
As far as the AOT and other differences between the schematic and the unit I have. Well there is a difference and I think even though the front of the box says 1061, the fact that the circuit board says 1161 tells me they are not entire the same. The gain blocks are and the general gain structure is, certainly the TX is but there are things I cannot reconcile between the two. I am going to roll with the schematic as reversing the ciruit is more than I am up to.
Hope this is helpful. Like I said, latere today I (should) be able to post the other info. It is not difficult now that we have the equations.
NOTE: This is only valid when the unit is in the Mic input positions. More than just a TX tap switch happens when it is switched. Some padding occurs on the rotary switches 'backside' R108 etc and that. This is also something I'll do the math on later.
EDIT:
Essentially it throws R108 or R108+R114 in a divider circuit with the 3k3 resistor following Av1
Brian
