# Thevenin Resistance query

I have an amplifier model circuit where I've determined the load (speaker) voltage (using its peak power output and its resistance) and measured the open-circuit voltage.

How can I work out the Thevenin resistance?

I am familiar with finding Rth when condensing a standard linear circuit but struggle to work backwards.

Any help or suggestions are much appreciated.

• $$R_{TH} = R_L \left( \frac{V_{OPEN}}{V_{LOAD}}-1\right)$$ Where V_open is a open-circuit voltage and V_laod is an output voltage with the load connected.
– G36
Apr 30 '20 at 8:28
• @G36 Thanks, much appreciated! May 1 '20 at 2:22

$$R_{TH} = R_L \left( \frac{V_{OPEN}}{V_{LOAD}}-1\right)$$