Hello,
novice here, I am building LED light organ from Jameco schematic and have some troubles understanding the circuit properly.

Although everything works fine (using lm741 and lm324 as ICs and 1N4007 diodes) I am not really sure about some components and what do they do. Here are the confusing ones:

1. C8/C9/C10 electrolytic capacitors - 2,2uF. Are they part of those second-order bandpass filters? As far as I know these filters aren't made of electrolytic capacitor at this positions.
2. C14. Might be there for the same reason as capacitors above but again, don't know why, please explain.
3. C15 what's it purpose in voltage divider?

Hope that someone will explain it to. Sorry in advance for terms I used, not sure if they are OK and understandable since English is not my native language.

 

C9, c10, c11 and C14 all are "coupling capacitors". They transfer a signal from one amplifier stage to another. The two stages can have a different DC offset and the capacitor transfers the AC signal that rides on the DC of each amplifier stage. However, c9, c10 and c11 also are part of high pass filters with the resistor just to the right of each capacitor.

C15 is there to stabilize the voltage divider. Any fluctuations of the power supply will be filtered out by this capacitor.

 

I got the C15 part and hopefully the "coupling capacitors" as well but could you explain the high pass filters? I was following this page:
http://www.swarthmore.edu/NatSci/echeeve1/Ref/FilterBkgrnd/Filters.html (at the bottom)
to calculate center frequency ([format: trimmer 25K-trimmer 0R], 176-225 Hz, 826-1 057 Hz, 3 755-4 805 Hz ) and have no idea how to include 2,2uF capacitors and 39K resistors.

 

I got the C15 part and hopefully the "coupling capacitors" as well but could you explain the high pass filters? I was following this page:
http://www.swarthmore.edu/NatSci/echeeve1/Ref/FilterBkgrnd/Filters.html (at the bottom)
to calculate center frequency ([format: trimmer 25K-trimmer 0R], 176-225 Hz, 826-1 057 Hz, 3 755-4 805 Hz ) and have no idea how to include 2,2uF capacitors and 39K resistors.

After looking at this again, the 2.2uF capacitors and the 39k resistors are filters but so low in frequency that they do not change the band pass at all (below 10 Hz). All they do is transfer the AC signal - ignore the filtering.

The resistor to the right of each coupling capacitor gives a DC path to ground for the capacitor as charge would only be able to leave the capacitor and the diode would block all charge from entering the diode.

 

Technically, each 2.2uF and 39K form a high pass filter. However, it;s cutoff freq is less than 2 Hz, so they can be ignored and don't participate in the three active filters.

ak