Something just kept bothering me with the circuit I built for Step 3. I read and re-read the section and although I still have some questions (more on that shortly), I knew that the amplification should work and I should be hearing more than the very faint buzzing noise coming from my speaker.
So, I went back to the circuit and then re-examined my breadboard... and there was the problem. Something very simple and easy to overlook. The circuit calls for a 100 ohm resistor in series with the loudspeaker. I made the mistake of putting in a 100k resistor. A factor of 1000! No wonder my loudspeaker was barely audible.
So, below you'll find a video with the newly substituted 100 ohm resistor. That annoying sound coming from my loudspeaker isn't so annoying anymore... I love that sound. It represents another lesson learned - always check your resistors with the multimeter to verify your color-coded selection is correct. As a matter of fact, I should ALWAYS be verifying my resistors with the multimeter against the circuit. On page 86, I went down the list and my brain just saw everything in k-units... R4 470K... R5 33K... R6 27K... R7 100K... oops... wait a minute. That's 100, not 100K.
I'm currently working on Step 4, but Step 3 still has me slightly confused. Back in Exercise 10 on page 80, we saw how a small current entering the Base amplifies the current exiting the Emitter. Okay, I get that. When the transistor is triggered at B, the current is amplified at E.
So, jump to page 91 and Figure 2-109. My first thought before building this circuit was that I'd simply rewire the loudspeaker and have one of its wires connected to the Q4 Emitter... more amps coming out would mean a louder volume, right? But that's not how it's wired up as you can see in Figure 2-109. That speaker wire is connected at the Q4's Collector. Huh? Still, I wired it up as shown in the schematic and it works. I think what I'm missing here is an understanding of how the speaker is oscillating... back in Figure 2-104 on page 86, I see the oscillation from the on-off of the 2N6027... the speaker is getting its voltage/current from the Cathode which turns on and off at a high frequency. But back in Figure 2-109, the speaker is no longer connected to the 2N6027 but instead is getting power directly from the 6V DC positive column (with R7)... so what's causing the speaker to oscillate now? L1 is going into the Collector of Q4 which is oscillating on-off... so is that on-off oscillation what now causes the speaker to buzz? I'm guessing yes, but I'm just not 100% understanding why... feel free to chime in if you have a good explanation.