gains with lm3886

Doovieman · 8th July 2005, 08:42 PM

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 · 8th July 2005, 08:53 PM

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 · 8th July 2005, 09:01 PM

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 · 8th July 2005, 09:19 PM

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

The application note can explain it clearer

Doovieman · 8th July 2005, 10:29 PM

Ahhhh, that makes sense.

SpittinLLama · 12th July 2005, 09:09 PM

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 · 13th July 2005, 05:04 AM

Quote:

Originally posted by 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

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

8th July 2005, 08:42 PM	#1
Doovieman diyAudio Member Join Date: Jul 2003 Location: Berkeley, California	gains with lm3886 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

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8th July 2005, 08:53 PM	#2
jaudio diyAudio Member Join Date: Oct 2004	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.

8th July 2005, 09:01 PM	#3
Doovieman diyAudio Member Join Date: Jul 2003 Location: Berkeley, California	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

8th July 2005, 09:19 PM	#4
jaudio diyAudio Member Join Date: Oct 2004	The combination of the mute resistor and caps causes a very small turn on delay. The application note can explain it clearer

8th July 2005, 10:29 PM	#5
Doovieman diyAudio Member Join Date: Jul 2003 Location: Berkeley, California	Ahhhh, that makes sense.

12th July 2005, 09:09 PM	#6
SpittinLLama diyAudio Member Join Date: Apr 2005 Location: In the Wild, Wild West	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

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