LM386....?

[reset]

Per 2nd schematic in the link below.

1) Expected DC voltages on pin 5 and pin 7, no AC signal input, Vs=12 volts?

2) Would rotating the volume control alter the said?

http://www.hobby-hour.com/electronics/lm...-audio.php

Excuse my ignorance on this matter.

Lawrence.[url=http://golbornevintageradio.co.uk/forum/newreply.php?tid=6474&replyto=70248][/url]

Someone here will tell you get the DC biasing right first and then look at the AC signal path. This is good advice but we sometimes  see circuit presented without the conditions being defined. I think the circuit is being presented for learning about the LM386 and not as a functional circuit. With no external circuitry pins 2 and 3 see ground through the 50K resistors. The output balances and pin  5 would be 1/2 Vs. Adding the volume control across pin 3 does not change the potential applied to pin 3 the circuit remains in balance.  If you apply a DC voltage to the volume control you will throw the circuit out of balance and cause the output to swing as you vary the pot.

   

The complete circuit might look like this ( from datasheet).

   

Note Cc, the coupling capacitor prevents DC from reaching the volume control while allowing the input to see AC excursion.  This preserves the circuit balance as far as DC bias is concerned while allowing the AC signal to be amplified. In a classroom we would spend time building the circuit possibly starting with a bridge circuit and onward. The site may have done that but with the wonder of web browser you can land in the middle of a thread.