In the block diagram what is the sigma symbol referring to?

I found a spreadsheet containing some values for LM3886 design. Can anyone of you please confirm it?
It already contains data that can be used to determine proper VA for traffo and proper heatsink, and independent variables like VCC, speaker impedance and crest factor can be changed values.

Here's the site http://www.neurochrome.com/taming-the-lm3886-chip-amplifier/thermal-design/
and the spreadsheet http://www.neurochrome.com/wp-content/uploads/2014/10/ClassAB_Calculator.xlsx

Great!

I was planning to buy a board from ESP but was still hesitant because of the cost.
Then, I found this kit. It is being sold here in the Philippines and costs only Php457 (about US$ 9.5). Reason for considering a kit is because I think it is easier to work with professionally made boards and that kit is so affordable.
Problem is, it says the Zobel network which is supposed to make it stable does the opposite so it removed those. Also, supply bypass caps are both 3300 uF (is this too large or any values will do?). Luckily, the board still has the holes for the Zobel RC.
Any comment on this kit?
Link is http://e-gizmo.com/oc/kits%20documents/LM3886%20audio%20amplifier/68WPowerAmpLM3886.pdf

so I can make R6 and R8 fixed with those values? And then add the trimmer to sub the 3 resistors.

How bout that section where the outputs of the two preamp and the input of the power amp meet?
What values of resistors are recommended there and what kind of connections?

Above is ESP Project 115.
I want my guitar amp (P27 Preamp and P19 Power Amp) to have an MP3 Input but since my player (smartphone) has low gain, I decided to add a preamp for the mp3 player inside the guitar amp.
Now, can I please ask for guidance what kind of circuit should I put in between the mp3 preamp to power amp, and guitar preamp to power amp. I think it might be better if it's illustrated but a clear explanation and guide is enough.

Also, I don't need that many resistors and the relay for the preamp since I'll only be using it for the mp3 player so I need it simplified too.

I was looking forward to experiment and find the right values for that RC circuit but to many values to choose from. Thanks Phil for narrowing the range.
I still wish I know the math though, can't find it in Google
Even then, math won't know my ears' preferences

ah the input also have polarized cap in series before the first resistor, Positive towards resistor

does the schematic of the p27 preamp have the supply bypass caps for the opamps or should I add it?
I didn't put 0.1uF caps there
or maybe Rod put it there but different values?

that's definitely a problem coz I don't know those values anymore. I removed those components some time ago and the board isn't labeled with values, only component type

Here's the datasheet application schem

I changed the input caps to 1 uF each coz that's what was available

Here's the layout and the actual board



In its old board (Yamaha PSR), I saw some kind of circuit before the input pin of the chip amp which looks like this

What does that section do? Is it a filter?

oh I see.
I'll make a filter for it then.
What kind? low pass? high pass?

I play keyboard while my phone's in my pocket, phone receives message keyboard speaker produces this sound like its amp receives another signal, phone signal. That's what happens, is that radio interference or not?
Amp is powered with a linear regulator (LM317 at almost 12V), input signal is from phone.

here's the link to datasheet
http://www.promelec.ru/pdf/LA4601.pdf

i removed the la4601 chip from my old yamaha psr keyboard and built a small amp based on its datasheet. (i can't attach datasheet since its in my laptop).
Anyway, the amp worked but it always produces this sound like when a message is coming to my phone near an amp. Of course, I tested the amp uncased so maybe shielding it will help. Or maybe you can recommend some mods to the datasheet schem to help remove those sounds. I will always be playing it with my phone.
Also, I think my phone's output level is too much for the amp coz most mp3's sound too distorted when my phone's volume is more than 10/30.
Does the LA4601 expect line/headphone level or not?
Sorry for posting this here. I know there are many forums where this topic is more suited but I'm at home in this forum. (more than any other)