Resistor values of stepped attenuator for BoSoZ

[stappvargen]

Hi,

I'm hoping that someone out there has already done the following and can give me som input!

Output section of BoSoZ:

---C1---R9--------
bbbbbbbbbb | bbb |
bbbbbbbbb R11 b P3
bbbbbbbbbb | bbb |
bbbbbbbbbb - bbb -
C1 = 10uF
R9 = 221 Ohm
R11 = 100 KOhm
P3 = 5 KOhm
(b = blank!)

The potentiometer P3 will be replaced by a ladder attenuator:
P3 => Rattenuator + R
where the signal out is:
Vout = R / (R + Rattenuator)

So... Now to my questions!
1) When R15 is set to 430 Ohm this
should give me 10dB gain according to N.Pass's article. Is the
10dB gain meant when P3 is at its maximum setting (i.e 5 KOhm)?
2) When using a ladder attenuator, as mentioned above,
and a small value of R is chosen (R = 100 Ohm), the value of resistor R9 (= 221 Ohm)
will have a large amount of voltage over
it and gain will be down by almost 10dB (i.e -10dB).
BUT, if R9 is set to 21 Ohm instead, gain will only be down by 2db
(-2db). (This is when Rattenuator is set to 0 Ohms.)
Is a value of 21 Ohms or thereabout acceptable for R9?
What is R9 good for anyway?

Thanks for your time.
/Niclas

 

[massimo]

It's a good question. I do hope somebody could reply.
I'm interested too.