I am making an amplifier and came across the fact that, if I want to operate a microphone then I will need a pre-amp.   What is the difference between power amplifiers and pre-amplifiers? Do both of them have the same gain, and if so then why do we need pre-amps?  Detailed explanation would be more more helpful to get the concept.
I find in many places mentions of pre-amplifiers being used to boost audio signals prior to feeding to a power amplifier.  Wikipedia's article on  gives some hints at their usage, but it doesn't really explain why it would be necessary to have two amplifiers in series rather than a single one with greater gain.  If a pre-amp is just a power amp with a smaller gain, what's the point, and why the distinction between the two kinds? Is the distinction in function, or simply purpose?
Sometimes (old) comments break the parser, so it would be nice to view their code to check what was (actually) supposed to be there. Is there any way to view a comment's source just like the source link in a post's revision?  edit Another application for this would be the ability to better quote comments in an answer without having to re-markdown them. Blender 2.8 - AWS EC2 command line EEVEE render I have been trying to get this to work for a couple days now. I have an EC2 P2 instance with NVIDIA CUDA configured by default, its a Deep learning Ubuntu AMI. This OS does not have a GUI so everything is via terminal.  I downloaded Blender's 2.8 TAR file for Linux and set it up on the EC2 instance. And ran the following command from the directory where the TAR file is extracted:   ./blender -b -noaudio /home/ubuntu/file.blend --render-output . --engine BLENDER_EEVEE --render-format PNG --verbose 4   All I see in the output is this:  Blender 2.80 (sub 75) (hash f6cb5f54494e built 2019-07-29 17:17:04) found bundled python: /mnt/blender/blender-2.80-linux-glibc217-  x86_64/2.80/python Read blend: /home/ubuntu/file.blend  Blender quit   Don't know why its quitting but I am unable to debug this any further. Any help would be appreciated.  UPDATE: As per @rjg's recommendation, ran the following command:  ./blender -b -noaudio /home/ubuntu/file.blend --render-output . --engine BLENDER_EEVEE --render-format PNG -f 1 --verbose 4   Got the following error:  Blender 2.80 (sub 75) (hash f6cb5f54494e built 2019-07-29 17:17:04) found bundled python: /home/ubuntu/blender/blender-2.80-linux-glibc217-  x86_64/2.80/python Read blend: /home/ubuntu/file.blend Unable to open a display Aborted (core dumped) show that $a^2+b^2+c^2+2abc+3\ge (1+a)(1+b)(1+c)$ let $a,b,c&gt;0$. Show that   $$a^2+b^2+c^2+2abc+3\ge (1+a)(1+b)(1+c)$$   By the $$(1+a)(1+b)(1+c)=1+a+b+c+ab+bc+ac+abc$$ it is suffient to show  $$a^2+b^2+c^2+abc+2\ge a+b+c+ab+bc+ac$$ How? My OpenID provider is shutting down; how do I change my Stack Exchange login? How do I make windows save their position on screen after re-attaching a display? macOS app for showing external HDD usage statistics? I'm planning on selling a used external HDD on eBay.  Are there any applications for Mac out there (preferably free) that can show me statistics about the usage history for the drive so that I can let potential buyers know the condition more precisely? I tried to use this for the last part of my table, but I can't get a vertical line at the end. Does anyone know?   \begin{tabular}{|CC|C|C|C|C|C|C|C|C|C|C|}\hline \Tab{Method Based on \\\hline       Radiography\\Magnetic Particle (A.C.)\\ \\Eddy Current\\Dye Penetrants\\ Ultrasonics} &amp; \Tab{ \\\hline \\ Wet \\ Dry \\ \\ \\ \\} &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Minute Surface Cracks }~}  \\\hline       N\\ G\\F\\F\\F\\P}  &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Deeper Surface Cracks      }~}  \\\hline            F\\G\\G\\G\\G\\G} &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Internal Cracks      }~}  \\\hline            F\\N\\N\\N\\N\\G} &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Fatigue Cracks      }~}  \\\hline            P\\G\\G\\N\\G\\G} &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Internal Voids      }~}  \\\hline            G\\N\\N\\N\\N\\G}           &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Porosity and Slag in Welds      }~}  \\\hline            G\\N\\N\\P\\N\\F}           &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Thickness      }~}  \\\hline            F\\N\\N\\P\\N\\G} &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Stress Corrosion      }~}  \\\hline            F\\G\\F\\N\\G\\F} &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Blistering      }~}  \\\hline            P\\N\\N\\N\\N\\F} &amp; \Tab{\rotatebox{90}{~\parbox{5cm}{Corrosion Pits      }~}  \\\hline            G\\N\\P\\N\\F\\P} \\\hline &amp; \multicolumn{11}{l}{G=Good;F=Fair;P=Poor;N=Not suitable.} \\ \hline \end{tabular} \label{tab:NDETechniques} \end{table}   It comes out like this: What happens to the view.frame.size attribute after a CGAffineTransform (Rotate)? What is the normal operating temperature for the MacBook (2016 generation)? Diamond moderator rollbacks can resurrect blacklisted tags Linux GUI development I have a large GUI project that I'd like to port to Linux. What is the most recommended framework to utilize for GUI programming in Linux? Are Frameworks such as KDE / Gnome usable for this objective  Or is better to use something more generic other than X?  I feel like if I chose one of Gnome or KDE, I'm closing the market out for a chunk of the Linux market who have chosen one over the other.  (Yes I know there is overlap)    Is there a better way? Or would I have to create 2 complete GUI apps to have near 100% coverage?  It's not necessary to have a cross-platform solution that will also work on Win32. Linux: coloring bash prompt will break carriage return When I try to colorize the bash prompt like this:  export PS1="\e[0;31m[\u@\h \W]\$ \e[m "   it breaks the carriage return (instead of going to a new line when line is full, it starts in the same line and erases the input text).  If I remove the color sequence it works fine. I use Ubuntu 11.10 and terminal (guake has the same bug too). Do I have to do something "special" to get the Color -> Color to alpha menu option to work in GIMP? I am trying to convert a background color on a GIF image to transparent by converting the background color to an alpha channel but the Color to Alpha menu option is not selectable.  I've gone through the GIMP documentation and it looks pretty simple :-) I must be missing something rather obvious here! How do I move Ubuntu dock to bottom on Ubuntu 17.10 and later? Just upgraded from Ubuntu 17.04 to Ubuntu 17.10.  Please help me to shift the side bar (aka Ubuntu Dock) to bottom.   I tried running the following command which used to work with older Ubuntu releases   gsettings set com.canonical.Unity.Launcher launcher-position Bottom   but it's not working. How do you check for whether a device is in a wifi deadzone? Collisions in space/vacuum Limit position rigidbody How can I limit the position of a rigidbody, between two values ​​if I use this code:  public Vector3 dir;  Rigidbody rb;  void Awake() {     rb = GetComponent&lt;Rigidbody&gt;(); }  void FixedUpdate() {     rb.velocity = new Vector3(0f, 0f, 6f);      rb.AddForce(dir * 1f, ForceMode.VelocityChange); }   If I use Vector3.Clamp then the object will shake List comprehension with expensive computation Interpretation of Shapiro-Wilk test I'm pretty new to statistics and I need your help. I have a small sample, as follows:    H4U   0.269   0.357   0.2   0.221   0.275   0.277   0.253   0.127   0.246   I ran the Shapiro-Wilk test using R:    shapiro.test(precisionH4U$H4U)   and I got the following result:   W = 0.9502, p-value = 0.6921   Now, if I assume the significance level at 0.05 than the p-value is larger then alpha (0.6921 > 0.05) and I cannot reject the null hypothesis about the normal distribution, but does it allow me to say that the sample has a normal distribution?  Thanks! EDIT: Summary  I think I've found the best definition of what I want thanks to the discussion with @M. Tibbits:  When I open or refresh the SO, I get a notification of new activities that are of interest to me. Today these are (hard-coded): answers to my questions and comments addressed to me. I want a bit more control over it, that's all.     Yes, I've read  and , but I think I add new (good :) ) reasons for re-asking it:  The first question was answered before this so handy "inbox" notification feature was implemented. So now using favorites for "watching" a question is wrong, IMHO, for 2 reasons:   it splits essentially the same functionality (of getting notified when there is an activity you are interested in) between 2 very different user interfaces it's cumbersome - I need to: 1) add question to favorites; 2) click on my profile dropdown; 3) click on the "favorites" line; 4) see all my favorites with recent activity; 5) select the one I watch; 6) repeat this process occasionally to get updates; and 7) possibly remove the question from favorites at the end. All this as opposed to this little red button when there are news.   Favorites are different in nature that watching. I add a question to Favorites when I find the answers useful to me in my work, so I may want to have it handy in the future. By watching an interesting question I will be able to decide whether I want it in faviorites, after I see the answers.  EDIT: I see that I was not clear enough.  I want to add a question to Favorites when:   it has some good answers the question and answers are relevant in my work I want to keep them handy as my long-term (persistent) knowledge base   I want to watch a question for short while (matter of days/weeks) when:   it is interesting / relevant I want to follow it to see what are the answers. Then I can decide whether I want it in my favorites   As you see, the main differentiators are good answers and long/short term. For short-term, automatic notification is better.  Bottom line, all I ask is "watch this question" checkbox (which may expire after say a week if there is a need to free resources)