Calling all LM3875 experts!
When I turn off my NIGC a loud 'thump' is heard from my 'speakers. I am not too happy about this and would like some input on how I can cure it.
Circuits wise it’s very simple like the 'typical app' circuit in the data sheet but without the 22uF Ci. Rf1 and Ri changed to 22K/681R respectively. I have followed lots of advise on this BB for the build but can't work out why this is happening.
The chip is supposed to mute when both supply rails drop below 12v. Looking at the 'scope a large DC offset is produced about 2 seconds after power off.
The supply is dual bridge and single 24-0-24 300VA TX, 2000uF on each rail with a further 1000uF hardwired to the chip pins and bypassed with 1uF. Rb is at 1K as per the data sheet.
Any ideas?
Many thanks in advance.
.
When I turn off my NIGC a loud 'thump' is heard from my 'speakers. I am not too happy about this and would like some input on how I can cure it.
Circuits wise it’s very simple like the 'typical app' circuit in the data sheet but without the 22uF Ci. Rf1 and Ri changed to 22K/681R respectively. I have followed lots of advise on this BB for the build but can't work out why this is happening.
The chip is supposed to mute when both supply rails drop below 12v. Looking at the 'scope a large DC offset is produced about 2 seconds after power off.
The supply is dual bridge and single 24-0-24 300VA TX, 2000uF on each rail with a further 1000uF hardwired to the chip pins and bypassed with 1uF. Rb is at 1K as per the data sheet.
Any ideas?
Many thanks in advance.
.
You could try putting some bleader resistors between your power supply rails and ground so that you PS caps are discharged through these to ground at swithch off. I have no real idea if this will help in this case or not, but I doubt it could hurt to give it a try if people don't come up with any other sujestions.
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