Thursday, May 13, 2010

Chapter 5 - Exercise 29

Apologies for delays in posting recently - throw in a small bit of procrastination with my mistakes in ordering incorrect components and ... you get the picture.

I got most of the schematic on page 251 wired up - it's a variety of colors, isn't it? I do believe there are a couple of mistakes here, but I'm not going to post them to the errata page until I get confirmation from a reader or from the author.

On page 251, for example, the 100microfarad smoothing capacitor for the 9V has the symbol of a nonpolarized capacitor, but the text says to use a regular electrolytic. I'm going with the text because of the author's explanation for WHY to use that type of capacitor...

Also, the 0.15microfarad capacitors are shown as NP type but not labeled as such... here, I'm going with the NP variety (that's all I have anyway) because of the symbol. Also, please note that that 0.15microfarad capacitors are not specified in the shopping list... I don't have any from previous experiments in the book, so I had to grab some of these locally.

I shot the photographs here before writing this up, so I also just noticed a mistake I made - the NP capacitor sharing the top part of the circuit with the coil is a 10 microfarad, not 100 as I've put in my circuit... fortunately, I haven't powered mine up yet... more on that in a moment.

I'm also wanting confirmation on something in the schematic - the 100microf coming out of pin 6 goes into pin 1... not connected to negative voltage as the other two 100 microf on pins 8 and 11. These are HUGE capacitors, and I'm very nervous about powering up this thing until I get that resolved as well... my initial thought was that that capacitor on pin 6 should at least have a connection to negative voltage, but maybe pin 1 is initially negative (a sink?)... again, not sure so I'm not powering up this bad boy just yet...

I've also got to pick up a headphone socket like the one in Figure 5-42 as well as some hardware to mount my 5" speaker to the plastic box. Will do that today.

We hear so much about audio and video equipment and the high voltages and currents they use/produce... so I hope you can understand my nervousness about plugging this breadboard in until I have all of these details ironed out... don't want a burned breadboard or any exploding capacitors in my vicinity... even with eyeshields on.


  1. James, the schematic symbol for a nonpolarized electrolytic capacitor is the same as for a nonpolarized ceramic capacitor, because they basically do the same thing.

    A 0.15uF capacitor is usually assumed to be ceramic (has been throughout the book so far) because they're cheap. When you get to higher values such as 100uF, it's cheaper to go with nonpolarized electrolytics that really contain two electrolytics back-to-back.

  2. The size of a capacitor is a function of a) its capacitance and b) its operating voltage, because a higher voltage requires thicker internal insulation, roughly speaking. In addition, NP electrolytic capacitors may be about double the size of polarized electrolytics because they really contain two capacitors.

    You should feel safer dealing with large capacitors than dealing with small ones!

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