LM3886 Mute Disable

[mothman]

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

[tschrama]

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.

Regards,

Thijs

[Guiness]

But I used a 8k resistor. I think there is a wide range of values to use in this situation.

[mothman]

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?

[Guiness]

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

[Taligent]

For another reference, Siegfried Linkwitz uses the following variation of the National application schematic, with a 38k resistor to disable mute functionality:



-Nikhil

[tschrama]

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.

Regards,

Thijs

[seangoesbonk]

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.

[mothman]

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,

[cybervagrant]

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.