# Finding gain in series of amps and attenuators

## Homework Statement

Please see the attached drawing. Find levels at A and B.

## Homework Equations

voltage gain in dB = $$20log(V_out/V_in)$$
dBu defined: $$20log(V/0.775V)$$

## The Attempt at a Solution

First question, since I know the level before the first amp, can I disregard the impedance of the source? So the gain and dBu at pos A would be:
$$V_{1-in}: -70dBu=20log(V_{1-in}/0.775V) \implies 0.775*10^{-70/20}=2.45*10^{-4}$$
Gain through first amp: $$20log(100/2.45*10^{-4}) \approx 112 dB$$
Level at pos A: $$-70dBu+112dB=42dBu$$.

is this right or have I done something terribly wrong?

I'm not quite sure how to get B. How can I figure out the gain of the second apmlifier, and thus the level at B before it turns to 0 dBu?

#### Attachments

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