The circuit on attached is a contour (variable loudness) circuit of Nakamichi 410 preamplifier. I’m wondering that why they used two sets of 22uf capacitors and 100kOhms resistors; C501, R501 and C503, R503. Are these components be buffer circuits? And why didn’t they place them after the switch to reduce the components, using only one set of R and C instead of using two for IN and OUT switch position?
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The switch changes the input of the volume pot and bypass the previous stage.
The capacitors block DC from the inputs and the 100k resistors discharge the caps to prevent a "crack" when switching.
A Buffer is an active circuit and needs at least one transistor or opamp. It doesn't amplify the voltage but has a high input and low output impedance
The capacitors block DC from the inputs and the 100k resistors discharge the caps to prevent a "crack" when switching.
A Buffer is an active circuit and needs at least one transistor or opamp. It doesn't amplify the voltage but has a high input and low output impedance
If I remove the switch from the circuit assuming there's no bypass path, can I eliminate the 100k resistors?
And, do I need to leave the capacitors at the same place?
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Perhaps there were shifts in the DC voltage level in the original circuit. When switching clicks. It is also a high-pass filter along with a potentiometer.
You can measure the voltage acoss the cap with a voltmeter. When it is <+/- 10mV you can try to take out the C and R. Or you leave both C and R.
Just looked again at the schematic and you can remove the 100k and leave the C if you have removed the switch. the pot is 100k to gnd.
Thanks very much. I found another circuit in its brother, Nakamichi 630, which has the same configuration as the 410's but without bypass switch. It was eliminated R but remained C as you mentioned.
May I ask one more question? What is the responsibility of R511 (470 Ohms)? It appears in both 410 and 630. How important is it?