Potato Cakes
Well-known member
Hello, everyone,
I've attached the main block of the schematic for an eight channel balanced to unbalanced PCB that I use for various applications, such as summing mixers. For a particular build I am doing for a client, the signal leaves the INA134 then goes to a on/off switch, then to the summing network (47k resistors) then to the summing amp. What I am confused about is when a particular channel is muted (signal is broken to the summing network) I still get a faint amount of signal from that same channel. In the grand scheme of real world use, it will never be noticed. But what I can't understand is how the signal is getting to the summing amp in the first place when the signal is being disconnected before the network. The best I can figure is that signal is somehow bleeding down the ground connection (all of the connectors have pin 1 tied together and going to the star ground) and is faintly being heard when referenced to the audio path. When I disconnect signal to the summing amp the faint signal bleed goes way, so I've at least narrowed it down to the INA137 circuit. I currently have the chassis and ground connections going to the star ground on separate connections. I had seen and read about separating audio and chassis ground with a 10 ohm resistor and a 100nF film capacitor connected parallel, but don't understand why.
What I have currently will be more than fine and I've had no complaints about crosstalk/bleed from other clients, but I'm always in pursuit of better understanding even though it causes me great mental pain.
Thanks!
Paul
I've attached the main block of the schematic for an eight channel balanced to unbalanced PCB that I use for various applications, such as summing mixers. For a particular build I am doing for a client, the signal leaves the INA134 then goes to a on/off switch, then to the summing network (47k resistors) then to the summing amp. What I am confused about is when a particular channel is muted (signal is broken to the summing network) I still get a faint amount of signal from that same channel. In the grand scheme of real world use, it will never be noticed. But what I can't understand is how the signal is getting to the summing amp in the first place when the signal is being disconnected before the network. The best I can figure is that signal is somehow bleeding down the ground connection (all of the connectors have pin 1 tied together and going to the star ground) and is faintly being heard when referenced to the audio path. When I disconnect signal to the summing amp the faint signal bleed goes way, so I've at least narrowed it down to the INA137 circuit. I currently have the chassis and ground connections going to the star ground on separate connections. I had seen and read about separating audio and chassis ground with a 10 ohm resistor and a 100nF film capacitor connected parallel, but don't understand why.
What I have currently will be more than fine and I've had no complaints about crosstalk/bleed from other clients, but I'm always in pursuit of better understanding even though it causes me great mental pain.
Thanks!
Paul