Yes, many threads generically on mute, repairing mute, but I have not seen a full description of all the catch-22's and solutions to do it well.
Many use relays. Issues, some resolvable, some not
Many use FETs or similar. Again, not without issues
But how big are these issues and how well mitigated?
Problem: Crossovers ( single supply) produce a speaker blowing thump on both power up and down.
Yes, one can stand around and wait to turn on the amp. ( I have a sequencer, so I sort of to that)
But, not only I impatient, but it does not resolve a power interruption.
So it needs to be a slow pic, fast drop kind of circuit. Soft switching, and not causing distortion to the signal as most FET designs can do.
Opto-couplers don't seem to have a high enough "off" . Stacked? But does that add Johnson noise? Various configurations of bleeder resistors, but again, noise, distortion etc.
The mute does not have to be perfect, just good enough. Drop has to be faster than the supply collapsing. Pick after the supply is stable and DC blocking caps are happy.
Modern low level circuits are in the .00-something or less distortion. Even my power amp ( mine, not the Parasound I am using) is even better. So small parasitic issues are relevant.
I have thought about cutting up the board and doing a tracking supply, but that is not perfect either. A good circuit could be used for either low level, or to pick a relay for speaker outputs. My old Creek does pop a bit.
Many use relays. Issues, some resolvable, some not
Many use FETs or similar. Again, not without issues
But how big are these issues and how well mitigated?
Problem: Crossovers ( single supply) produce a speaker blowing thump on both power up and down.
Yes, one can stand around and wait to turn on the amp. ( I have a sequencer, so I sort of to that)
But, not only I impatient, but it does not resolve a power interruption.
So it needs to be a slow pic, fast drop kind of circuit. Soft switching, and not causing distortion to the signal as most FET designs can do.
Opto-couplers don't seem to have a high enough "off" . Stacked? But does that add Johnson noise? Various configurations of bleeder resistors, but again, noise, distortion etc.
The mute does not have to be perfect, just good enough. Drop has to be faster than the supply collapsing. Pick after the supply is stable and DC blocking caps are happy.
Modern low level circuits are in the .00-something or less distortion. Even my power amp ( mine, not the Parasound I am using) is even better. So small parasitic issues are relevant.
I have thought about cutting up the board and doing a tracking supply, but that is not perfect either. A good circuit could be used for either low level, or to pick a relay for speaker outputs. My old Creek does pop a bit.
The quiet and effective solution is to use a 555 timer driving a relay. A telecom relay will short line level with no clicks or pops. The circuit is completely silent and simple. Use a series resistor before the relay to limit peak current.
Douglas Self's book "Small Signal Audio Design" discusses mixing console circuits including non-instantaneous muting. He uses JFETs optimized for Analog Switch applications, such as the Fairchild J111 (datasheet), to gradually ramp up and ramp down the resistance of the analog switches which implement muting and multiplexing. Resistance gradually ramps between "infinity ohms" (really: leakage currents) and "zero ohms" (really: RDSon = 30 ohms), over the span of a millisecond. So there is no click. There are other JFETs with even lower RDSon, when you allow yourself to use surface mounted transistors.
"non instantaneous muting"
I must try this.
The radio in my old Subaru had ramp up/ramp down volume when turned on or off. Ramp time about 1.5 seconds. I never thought about it because I have always eschewed solid state muting circuits.
I must try this.
The radio in my old Subaru had ramp up/ramp down volume when turned on or off. Ramp time about 1.5 seconds. I never thought about it because I have always eschewed solid state muting circuits.