audio amplifier repair question.

[Oddball]

Hello, recently I have been repairing an 5.1 surround amplifier (onokyo ht r8230). I have the service manual with detailed schematics but I have a question on the block diagram. From what I see the sound from the RCA jacks / tunner is amplified by 6db then attenuated by 18 db then amplified again by 27 db in the driver amp. Question is, why amplify by 6db then attenuate by 18? Why not just attenuate by 12db? Ive attached screen shots of the block diagram below, if need be I can post detailed transistor level schematics from the service manual.

[PA0PBZ]

If you are referring to the "0-18dB" text I'm sure you should read it as "0 to 18" and not -18.

[Oddball]

In that case, what is 0/6db supposed to mean?

[PA0PBZ]

In that case, what is 0/6db supposed to mean?

switchable between 0 and 6 dB, unlike the others that have a variable resistor in the input.

[Oddball]

Well the power amp has fixed gain of 27dB...which means at standard 1.4vrms RCA voltage levels the lowest voltage it could output would be 31 volts rms, which seems unlikely, how exactly is volume controlled then?

[SoundTech-LG]

Volume is controlled by that master volume chip, which in your block diagram not everything is shown, there is much more detail on the actual schematic diagram. do you have it???

[PA0PBZ]

Just on the back of the envelope: If you have 100W output and 27dB gain you need an input of 200mW.Since the RCA will have an input signal a lot lower than that you will need additional amplification. If you know the input impedance you can calculate the input power for 1.4V

[Oddball]

I will attach photos of the preamp, note the mux/volume  chip is actually broken (BD3811K1) and im building logic to bypass it.

I'm on my phone at the moment and I can post more detailed pictures when I get home.