[AudioI] Audio Injector Isolated RCA Breakout Full Scale Input Amplitude

[Matt Flax]

Hi there,

There is a 3k Ohm resistor going to the input of the op-amp on the input 
side of the RCA preamplifier. The input is unbalanced. The op-amp has a 
3.57k Ohm resistor in negative feedback. Which is a gain of 3.57/3 = 
1.19. Check here : 
https://en.wikipedia.org/wiki/Operational_amplifier#Inverting_amplifier

The total input stage has a 7.4 dB gain. That is equivalent to 2.34 
times the input voltage (2.34=10^(7.4/20)). This is double the 
unbalanced opamp's gain because we go from unbalanced to balanced 
(differential) into the audio codec.

The maximum peak to peak input voltage would be roughly the same as the 
output voltage.

That is around 2.1v peak to peak.

There are no AC coupling caps on the input. It can amplify from DC up. 
The DC resistance is as mentioned above - the resistance seen for the 
inverting opamp stage.

If people are interested, we can create a preamp together ?

Matt

On 10/10/21 2:33 pm, Jonathan wrote:
> Hi All, Matt,
>
> It's mentioned in the spec of the Audio Injector Isolated that the 
> full scale input voltage is 5.65Vp-p. Since the schematic of the RCA 
> breakout board is not public, is the full scale input voltage of the 
> RCA breakout the same?
>
> Also, what is the DC resistance of the RCA breakout board input that I 
> should expect to see?
>
> Thank you.
>
> Jonathan
>
>
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