Hafler FET Muting Circuit

[GeorgeP]

Those two FETs at Q15 have to go. They do degrade the audio a tad and can go "leaky" reducing the output level. Sometimes they short completely and the channel is dead!
I removed the FETs and put a relay there instead. Much better.
I used a 5V DC low current relay with the coil tied to ground through a 17V Zener diode. The other side of the coil goes to the output pin of the comparator.
After 5 seconds or so, the output pin of the comparator goes to -23V, AND THE RELAY CLOSES. At 5/6 volts across the coil the relay current is only 11 milliamperes, easy for the comparator to handle, and low dissipation for the Zener diode (0.190 W. with a 0.500 W rating).. The contacts short the output to audio ground, the same way the original FETs did, with MORE attenuation, and less distortion and loss. Use a diode across the coil in reverse bias, for the coil current release transient.

 

[fransa]

The Hafler FET muting circuit helps reduce noise when turning an amplifier on or off. It uses special electronic parts called FETs (Field-Effect Transistors) to mute the sound for a moment, stopping any loud pops or clicks for smoother sound.

 

[J!m]

Wow! Spam botanist!

 

[GeorgeP]

The Hafler FET muting circuit helps reduce noise when turning an amplifier on or off. It uses special electronic parts called FETs (Field-Effect Transistors) to mute the sound for a moment, stopping any loud pops or clicks for smoother sound.

It's an ok circuit, but can be non-linear when the devices are compromised. They go very leaky, even short during AC line spikes from local lightning strikes. Been there...
I removed those two FETs from my two Haflers and put in a sealed DPST Relay. Much better. My new GPulseLinear Preamp design uses these sealed relays on sockets. Using them for source switching also. Sound quality is better.

 

[J!m]

You're walking through the botanical garden there George!