Hi, few questions about the input and output opamp circuits of a preamp.
Mostly copied from marantz receiver schematic.
Input:
- gain 3
- 22k input impedance? Want to keep it low for low noise, but is it ok?
- input Cap, wanted to omit it, but keep it safe.
- what is the purpose of R1 (470 ohms), and how to calc it?
- C2/3 should be some RF filters, as far as I know.
Output
- coupled to TC9459 vol control IC.
- 68k input impedance (marantz sr5200 as a reference)
- unity gain
- missing resistor on input (like the input stage).
Originally there is 470 ohm resistor in the marantz sheme. Purpose, value?
- coupling cap C1. Can I ommit it?
What if there is a DC offset and some constant current flow in the output of TC9459?
Would it cause the vol chip to distort?
P.S. I plan to put these circuits on one PCB with a common ground polygon.
This way it would be the closest to the input and output terminals.
I think I posted it in the wrong section...
Mostly copied from marantz receiver schematic.
Input:
- gain 3
- 22k input impedance? Want to keep it low for low noise, but is it ok?
- input Cap, wanted to omit it, but keep it safe.
- what is the purpose of R1 (470 ohms), and how to calc it?
- C2/3 should be some RF filters, as far as I know.
Output
- coupled to TC9459 vol control IC.
- 68k input impedance (marantz sr5200 as a reference)
- unity gain
- missing resistor on input (like the input stage).
Originally there is 470 ohm resistor in the marantz sheme. Purpose, value?
- coupling cap C1. Can I ommit it?
What if there is a DC offset and some constant current flow in the output of TC9459?
Would it cause the vol chip to distort?
P.S. I plan to put these circuits on one PCB with a common ground polygon.
This way it would be the closest to the input and output terminals.
I think I posted it in the wrong section...
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I got what it is about:
R1/C2 is a RF lowpass filter.
In the original Marantz circuit it is set at ~3.4 Mhz rollof.
I am going to have Arduino Nano MCU controlling the device.
Clock frequency - 8 Mhz (if not mistaken).
Shoud I aim at 4 times lower rollof for the lowpass (2 Mhz)?
Should I put such a lowpass on each and every opamp in my device?
Or just on the opamps with gain?
(lot of the opamps are unity gain or rollof filters).
R1/C2 is a RF lowpass filter.
In the original Marantz circuit it is set at ~3.4 Mhz rollof.
I am going to have Arduino Nano MCU controlling the device.
Clock frequency - 8 Mhz (if not mistaken).
Shoud I aim at 4 times lower rollof for the lowpass (2 Mhz)?
Should I put such a lowpass on each and every opamp in my device?
Or just on the opamps with gain?
(lot of the opamps are unity gain or rollof filters).
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