Weird LM3886T problem

[Atilla]

Originally Posted by AndrewT

no!
if the input offset is zero then there is a residual output offset. This is the input offset current times Rin times stage gain.
If there is an input offset, the residual offset and the input offset add (algebraically) together.

Sorry, my bad, AndrewT is correct. I was hasty at replying.

[pacificblue]

Originally Posted by AndrewT

The AC coupling of the input can be at EITHER the source or at the power amp, but not both.

Nearly all commercial sources have AC-coupled outputs, and most amps have AC-coupled inputs, because AC-coupling is the safer solution. Having both the source and the amp AC-coupled may be unnecessary, but it does not hurt from a safety point of view.

From a sonic point of view it is preferrable to either have only one filter or have the same corner frequency on all filters, if there are several. Lamentably there is no norm, regulation or even agreement among manufacturers that would ensure that.

Only few non-pro amps have a selector to choose from AC- and DC-coupled operation. With such a selector you still need a schematic or to open up the sources to find out whether they are AC- or DC-coupled. Then you have to instruct everybody, who may use the amp, which source needs AC- and which DC-coupling.

The two ways out of this are
- AC-couple the amp, like most manufacturers do. Simple, cheap and reliable.
- use a source selector with an additional contact layer that you can hardwire for the right setting with each source. Takes a more expensive selector and/or additional relays in return for a sonic improvement that is hardly noticeable, if at all. And don't forget to check and maybe rewire the circuit, when you replace a source.