Two-Stage Audio Amplifier

Thread Starter

elec_eng_55

Joined May 13, 2018
214
I have been looking at two-stage audio amplifier circuits and running them in LTSpice.
When I look at the output graph, the output voltage is always riding on a dc level despite the coupling capacitors. The problem, whatever it is, is in the 2nd stage. In the real world I can see this happening if you if a leaky coupling capacitor but in a simulation? I have tried many versions with the same result each time. Any ideas on
why this might be happening?
 

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Last edited:

AlbertHall

Joined Jun 4, 2014
12,345
The circuit has coupling capacitors and it will take some time for them to settle to their final voltages. Make sure you are looking at a time after that has happened, perhaps 1 second.
 

Thread Starter

elec_eng_55

Joined May 13, 2018
214
The circuit has coupling capacitors and it will take some time for them to settle to their final voltages. Make sure you are looking at a time after that has happened, perhaps 1 second.
Thanks Albert.

Does the LTSpice software actually take that into account?
 
Last edited:

Jony130

Joined Feb 17, 2009
5,487
the output voltage is always riding on a dc level despite the coupling capacitors.
At which point of a circuit?
Because only at the output you well see AC swing witch zero DC offset.
But for example, the AC voltage at the Q2 base will always swing up and down around 2V.
 

Audioguru

Joined Dec 20, 2007
11,248
Why is the input signal level only 0.5mV peak and the output signal level also almost nothing?
Why is the load on each transistor (2k for the first transistor and 10k for the second transistor) so low that each transistor collector is overloaded?

With a half-decent input and output signal level then the output is severely distorted.
 
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