Exactly.
The input impedance is 10k per channel. Each 10k resistor sees a ground voltage. So it is like the 10k resistor is connected to ground. Hence the 2 resistors do not influence other.
Did you intend R3 as the gain adjustment with a variable resistor. It will work. Gain can be adjusted between 0 and 5. If you don't want the zero gain, put a 10k resistor in series with R3 and the gain can be varied between 1 and 6. You get the idea.
Just wanted to say again, there was nothing wrong with your previous circuit. A separate pot followed by a buffer amp. If you have that buffer amp available anyway.
The input impedance is 10k per channel. Each 10k resistor sees a ground voltage. So it is like the 10k resistor is connected to ground. Hence the 2 resistors do not influence other.
Did you intend R3 as the gain adjustment with a variable resistor. It will work. Gain can be adjusted between 0 and 5. If you don't want the zero gain, put a 10k resistor in series with R3 and the gain can be varied between 1 and 6. You get the idea.
Just wanted to say again, there was nothing wrong with your previous circuit. A separate pot followed by a buffer amp. If you have that buffer amp available anyway.
Uhm there is some confusion.
The schematic in your post #40 for the summation is way better. Keep it.
Then, regarding the gain, the schematic in #40 will work.
I just looked again to your schematic from #37. I thought the gain adjustment was different, using a simple potmeter. I was wrong in recalling the schematic. Looking at it again I am not sure I understand it. Gain control using a potentiometer is usually done like this:
The values of R12/R13 should be at least 10x higher than the the potmeter. If they are smaller, the potmeter linearity will be affected. Min and max gain are still the same. But 50% won't be in the middle.
The schematic in your post #40 for the summation is way better. Keep it.
Then, regarding the gain, the schematic in #40 will work.
I just looked again to your schematic from #37. I thought the gain adjustment was different, using a simple potmeter. I was wrong in recalling the schematic. Looking at it again I am not sure I understand it. Gain control using a potentiometer is usually done like this:
The values of R12/R13 should be at least 10x higher than the the potmeter. If they are smaller, the potmeter linearity will be affected. Min and max gain are still the same. But 50% won't be in the middle.
Yes, #40 is good.
The minimum input impedance depends on the source you use. Few sources complain with 10k. Standard is 47k for audio. Noise won't be a problem even if you make resistors 10 times larger.
OTOH you don't want a very high input impedance because the inputs will be susceptible to noise coming from the cable etc. I used 12k for my amplifier and that was mainly because of the potmeters I had available.
If you drive your circuit from an opamp output 10-50k imput impedance is ideal.
The minimum input impedance depends on the source you use. Few sources complain with 10k. Standard is 47k for audio. Noise won't be a problem even if you make resistors 10 times larger.
OTOH you don't want a very high input impedance because the inputs will be susceptible to noise coming from the cable etc. I used 12k for my amplifier and that was mainly because of the potmeters I had available.
If you drive your circuit from an opamp output 10-50k imput impedance is ideal.