Lm3886 with single ended supply

[pacificblue]

1. • The 10 Ohm resistor should be bigger. I should say at least 3 W.
   • 1/4 W should be enough for the Zobel. If it burns, something is wrong and you should not increase the wattage until it holds, but find out, why the amp is oscillating.
2. 10k to ground should do
3. • You need both. 1000 µF for storage and 100 nF right next to the LM's supply pins for decoupling.
   • Film caps will be okay, if they have the right voltage rating. They both should be rated for the rail voltage, because in some situations the entire rail voltage can be present on them. The reason why electrolytics are drawn may be that film caps with sufficient voltage rating were not available or unseemly expensive at the time the datasheet was written.
   • A film cap is better in that place, but you need to watch the voltage rating, because this must be rated for the rail voltage plus whatever negative potential can be present on the source.
4. • Rn = Rin? That is signal ground. With single supply however you do not have signal ground the same way as with split supply. The reference for all signals is pin 7, not the ground.
   • Both Ca are signal ground, because they belong to the circuit that sets the reference at half supply.
   • Ci belongs to the feedback loop which makes it signal ground. Csn is power ground. Both should however be grounded near the LM to keep inductance low.
     In theory Cm is signal ground, but such a big electrolytic capacitor connected to signal ground will make many people uneasy. Its function makes it uncritical with regards to the ground, so you can connect it to power ground as well.
   • Yes.

 

[dmtparker]

Thanks. I am assuming I can use pin 7 as the star signal "ground" for the chip and attach it as well as input and output ground to a star and then to chassis via a thermistor or small resistor.
One question: do I make the signal star right @ pin 7 or on the ground side of Ca? Also, the first Ca (the one || Ra=100k) attaches directly to pin 4 and to "ground". Is this ground also signal? (I thought it would be power since pin 4 is where the neg rail usually connects.)

 

[pacificblue]

What function has a thermistor between chassis and ground?

Pin 7 is at half supply and ground is at 0 V. Answer this for yourself. What will happen, if you connect pin 7 to the star ground?

With single supply the concept of signal and power ground does not apply in the same way as with split supply. The only direct ground connection to the chip is pin 4 and that is power supply, so it is power ground. The first Ca belongs to the circuit that sets the signal reference at half supply, so it should be signal ground. Don't let yourself be confused by the way it is drawn. Everything that is connected to ground connects to pin 4. The separation between signal and power ground does not change that. It only changes the routing with the aim to put some more space in between different return currents.

 

[dmtparker]

OK, so we use pin4 for power ground and others are connected to it via the caps shown. The input and output gnds (RCA in, 5 way out) are also connected to power gnd or "float"?
I had used thermister to keep signal ground above earth to avoid loops. (It is between signal ground and chassis, not chassis and earth)