LM3886 with mute relay still popping ?

iggy111 · 28th January 2013, 06:51 PM

I added two relays as muting switches on my LM3886 amp, 12V / 16A Schrack units, powered from an independent small PSU, which is connected to a mechanical switch on the chassis, so I turn the amp on, and then unmute it.

The amp is totally silent during power on, but pops relatively loud when I mute it. Is there a way to reduce this pop, maybe by adding a "snubber" to the relay? I read here that this is exactly what reduces pops from a normal switch, but could someone tell me what values should I use for R and C?

Switch contact design : Switches

djoffe · 28th January 2013, 08:01 PM

Please clarify how you are muting...with a relay interrupting the speaker connection? With a relay changing the current in/on of the mute pin?
A little of both?

iggy111 · 29th January 2013, 12:10 PM

Relays are used on the mute pin, between Rm and V-, not on the speaker connections.

djoffe · 29th January 2013, 01:06 PM

Please post a schematic. The most likely cause of the popping is a change in the output voltage between muted and non-muted states. The output voltage follows the voltage on pin 7 when the part is muted. It follows the voltage on the non-inverting input when the part is not muted.

If these voltages are different, then you get a pop. Of course, you'll also get a pop even if the only difference between the two is some offset voltage, but the pop should be smaller.

So....please post schematic, and perhaps I can refine my guesses and see if they make sense.

Akitika GT-101

28th January 2013, 06:51 PM	#1
iggy111 diyAudio Member Join Date: Feb 2007 Location: Zadar, CRO	LM3886 with mute relay still popping ? I added two relays as muting switches on my LM3886 amp, 12V / 16A Schrack units, powered from an independent small PSU, which is connected to a mechanical switch on the chassis, so I turn the amp on, and then unmute it. The amp is totally silent during power on, but pops relatively loud when I mute it. Is there a way to reduce this pop, maybe by adding a "snubber" to the relay? I read here that this is exactly what reduces pops from a normal switch, but could someone tell me what values should I use for R and C? Switch contact design : Switches

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28th January 2013, 08:01 PM	#2
djoffe diyAudio Member Join Date: Oct 2008	Please clarify how you are muting...with a relay interrupting the speaker connection? With a relay changing the current in/on of the mute pin? A little of both?

29th January 2013, 12:10 PM	#3
iggy111 diyAudio Member Join Date: Feb 2007 Location: Zadar, CRO	Relays are used on the mute pin, between Rm and V-, not on the speaker connections.

29th January 2013, 01:06 PM	#4
djoffe diyAudio Member Join Date: Oct 2008	Please post a schematic. The most likely cause of the popping is a change in the output voltage between muted and non-muted states. The output voltage follows the voltage on pin 7 when the part is muted. It follows the voltage on the non-inverting input when the part is not muted. If these voltages are different, then you get a pop. Of course, you'll also get a pop even if the only difference between the two is some offset voltage, but the pop should be smaller. So....please post schematic, and perhaps I can refine my guesses and see if they make sense. Akitika GT-101