Diagram of a 2.1 preamplifier joined to an audio power amplifier, taken from a YouTube project; the doubled pdf extension is just a naming slip. The 85.6 KB PDF is useful for hobby builds or for tracing the signal from input through the preamp to the power stages. Because hobby video designs are rarely formally verified, check component values, supply voltage and the pin numbering of the amplifier ICs against datasheets before soldering.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @pdf_servicemanual. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.
Any PDF readerSumatraPDFFirefox / ChromeFlexBV (links PDF to boardview)