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Old 29th April 2003, 06:59 PM   #1
mothman is offline mothman  United States
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Default LM3886 Mute Disable

Hello,

I'm using a LM3886 based Clone with the mute circuit currently functional.
I'm planning some ongoing tinkering and wanted to disable the mute function,eliminating the extra caps,resistors and wire.
I have the data sheets and have spoken with NSC who say a jumper from the mute pin 8 to the V- pin would do the trick.
Just wanted to see if anybody has successfully done this as I don't have any extra chips to burn!

P.S I hope this question is intelligent enough to garner a response as my other inquiry re: power supply caps may have been judged too stupid for some of you geniuses
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Old 29th April 2003, 10:46 PM   #2
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I have used the LM3886 for a GainClone and to disable the mute function and jumpered with a 10K resistor to limmit current from mute pin direct to Vsupply. Very easy, no wires.

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Thijs
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Old 29th April 2003, 11:36 PM   #3
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Default Same here...

But I used a 8k resistor. I think there is a wide range of values to use in this situation.
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Old 29th April 2003, 11:37 PM   #4
mothman is offline mothman  United States
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Greetings,

I very much appreciate your help.Did you notice any change in your amps performance?
Mine actually sounds very good and after many trials with grounding schemes is also very quiet.
I certainly don't need the mute and can only surmise that the amp should sound better without the added circuitry.
Lastly I have some very nice 20k Richen Ohm resistors would that be too much?
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Old 30th April 2003, 04:48 AM   #5
Guiness is offline Guiness  United States
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Default Save the riken comp resistors...

All you are doing is disabling the mute function. The quality of the resistor will do nothing to performance. The value on the other hand I am not familar with. I have only used the 8k, nothing else. Goodluck
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Old 30th April 2003, 06:32 AM   #6
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For another reference, Siegfried Linkwitz uses the following variation of the National application schematic, with a 38k resistor to disable mute functionality:

Click the image to open in full size.

-Nikhil
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Old 30th April 2003, 08:03 AM   #7
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The resistor value has a effect on the muting. There should flow some significant current through the resistor (1mA?): check the datasheet for the recommended current: then calculate the resistor needed with your Vsupply.

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Thijs
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Old 1st May 2003, 03:09 AM   #8
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Quote:
Originally posted by tschrama
The resistor value has a effect on the muting. There should flow some significant current through the resistor (1mA?)
This is true. You must draw more than 0.5mA out of the mute pin.

Resistor = (|Vee| - 2.6v)/I

"I" must be larger than 0.5mA.



For example, if your Vee is -25v , then:

R = (25 - 2.6)/0.5mA

R must be less than 44.8 Kohm.
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Old 1st May 2003, 07:29 PM   #9
mothman is offline mothman  United States
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Eureka!!

I went with the 10k resistor accross pin 8 and V- and it seems to work just fine.
All the vitals measure the same including vanishingly low DC offset at the output of 01.5 mv dead on for both channels.
I'll let in run in for a while and report back on any change in sound.
Thanks everyone for your input and the schematic I think Tallman included,most interesting.

Regards,
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Old 19th May 2003, 01:38 PM   #10
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I spoke with an engineer at Nationals audio division. To disable mute all you need is a resistor to provide the necessary current between the proper pins, pin 8 and 4 I think for the 3876. The value of the resistor depends on the supply voltage, read the data sheet for the exact calculation. You need to have some thing like 0.5mA or more flowing out of pin 8. Too much current might damage the chip, so I would recommend keeping the resistor, Rm. The capactor, Cm, may be omitted, if mute will be permanently disabled.
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