Hi all,
I am looking at the power amp schematic for the Harman Kardon 330c receiver. My question is with regards the circuit comprised of the following components:
C402, R402, C404 and R404.
I just don't understand the circuit. On one hand the resistances make me think of DC operation of the Q402, from another perspective I see C402 as just a decoupling capacitor which in series with R402 is used to somehow set the input impedance of the amplifier and don't really have any idea what the C404/R404 parallel circuit does with the exception that R404 might has something to do with the DC operation of the BJT.
Can you please, help me understand this better?
Thanks in advance.
Soundork
I am looking at the power amp schematic for the Harman Kardon 330c receiver. My question is with regards the circuit comprised of the following components:
C402, R402, C404 and R404.
I just don't understand the circuit. On one hand the resistances make me think of DC operation of the Q402, from another perspective I see C402 as just a decoupling capacitor which in series with R402 is used to somehow set the input impedance of the amplifier and don't really have any idea what the C404/R404 parallel circuit does with the exception that R404 might has something to do with the DC operation of the BJT.
Can you please, help me understand this better?
Thanks in advance.
Soundork
R402, R404 and C404 are a high frequency low-pass filter network to shunt RF from entering the circuit. C402 is to block D.C. from entering.
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Complementing....R404 serves as DC path for Q402 base (goes to ground = 0V).
Note that R404 has the same value of R414 which plays 2 roles: feedback and DC path for Q404 (0 at output so same as ground).
Since Q402 and Q404 make the differential amp, their DC paths on transistor's base needs to be the same so as to minimize DC offset in the output.
Note that R404 has the same value of R414 which plays 2 roles: feedback and DC path for Q404 (0 at output so same as ground).
Since Q402 and Q404 make the differential amp, their DC paths on transistor's base needs to be the same so as to minimize DC offset in the output.