gains with lm3886

[Doovieman]

Hi-
I've made an amp with lm3875 and several prototypes using the same chip. I'm starting a new amp and the lm3886 looks interesting. I was wondering what gains people were using. The data sheet says that gains between 20-200 should suffice. My initial thought was to use a gain of 20 as I had with the lm3875.
Is there a general consensus as to what gain to use with the 3886? There are of course obvious tradeoffs, but I'm curious to see what others think.
Also, I've never used the mute feature before. Do people typically have a physical mute switch or use an analog switch IC with a simple microcontroller or mechanical switch for control?

Thanks,

Doovieman

 

[jaudio]

A gain of 20 in OK. The gain is usually set bewteen 10 and 20. If you use a preamp with gain choose bewteen 10 and 13.

Very few builder I seen use any switch at all. You can use it for the little delay by using a resistor and caps.

 

[Doovieman]

Thanks for the note. I'm not sure i understand what you mean with regards to the mute and a delay. Can you explain a little more clearly? Thanks,

Doovieman

 

[jaudio]

The combination of the mute resistor and caps causes a very small turn on delay.

The application note can explain it clearer

 

[Doovieman]

Ahhhh, that makes sense.

 

[SpittinLLama]

Don't use a gain less than 10V/V on the LM chips and for best Noise performance keep the gain below 50V/V. If you need more gain then run a preamp that is high quality and reduce the gain on the LM3875 or LM3886 that you are using.

-SP

 

[peranders]

Thanks for the note. I'm not sure i understand what you mean with regards to the mute and a delay. Can you explain a little more clearly? Thanks,

Doovieman

If you check my QRP02 design (see my homepage) you can see how I have done the mute thing.

At power-up the LM chip is turned off totally under 12 V and over 12 V it starts to come alive but with shut off input stage which ends up in heavy attentuation. The datasheet has a diagram over current out from Mute pin vs. attenuation.

The result of my design is a completely silent turn on and since the buffers work under 12 V I have also a totally silent turn off.

I have used a bit higher value of the mute resistor in order to get a longer delay with choosed cap.

The mute and undervoltage feature is a really nice feature