For another perspective on simulators, google [Bob Pease Spice] you will find a number of articles including the original one by Bob Pease explaining why he feels that spice may not always be trustworthy......
Thanks for the explanation Peter. I notice the 2 3.3K resistors form a voltage divider with the middle being 1/2, and I knew that resistor connected to the speaker lower it's volume but I didn't know it was a current-limiting resistor. How did you calculate those 4.4V and 2V values?
Whiteoxe, water water everywhere and not drop to drink.
You can do that in your head as the npn is in emitter follower mode and is essentially a voltage buffer except there is always a 0.6V Vbe drop, So the voltage at the junction of the 2 identical resistors will either be half Vcc or Vcc. That means 2.5V-0.6 = 1.9V or 5V-0.6 = 4.4V. That's a simplistic analysis of the circuit because there is also the combined Rbe + emitter load which in the case of the KIM-1 is ~25(Rbe) + 27(R) + 8 (speaker) = 60 * Hfe (~100) = 6000. So this would tend to load the input divider and so the voltage swing is probably more like from 1.3V to 3.3V but I could verify this on a sim to be sure. The 27R does reduce the volume but it also reduces the current as the speaker may not be able to continuously handle the full voltage and current plus resultant DC magnetization too.
Peter, if theres time, Id like us to compare LTspice and Yenka. LTSpice is asking me questions that I’m not sure what the answers are . Any way I hope we can get the vostro power input solderin. I really like that dell laptop ;_)
Comments
You can do that in your head as the npn is in emitter follower mode and is essentially a voltage buffer except there is always a 0.6V Vbe drop, So the voltage at the junction of the 2 identical resistors will either be half Vcc or Vcc. That means 2.5V-0.6 = 1.9V or 5V-0.6 = 4.4V. That's a simplistic analysis of the circuit because there is also the combined Rbe + emitter load which in the case of the KIM-1 is ~25(Rbe) + 27(R) + 8 (speaker) = 60 * Hfe (~100) = 6000. So this would tend to load the input divider and so the voltage swing is probably more like from 1.3V to 3.3V but I could verify this on a sim to be sure. The 27R does reduce the volume but it also reduces the current as the speaker may not be able to continuously handle the full voltage and current plus resultant DC magnetization too.