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Old 21st May 2013, 03:59 PM   #1
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Default how to unmute LM3886 ?

I have got LM3886 but its not getting unmute.
Please suggest Rm value for power supply of 18-0-18 dc.

When i disconnected Rm and left the pins untouched, there was only a little sound and that too even in max. input signal (full volume), indicating it to be in a mute condition.

I have seen datasheet and tried 22k, 10k, 5k,and 1.5k, but its still mute.

The rest schematics are according to figure1 of datasheet
CHANGES: replaced 22u with 47u and omitted Cm.

Please reply soon!
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Old 21st May 2013, 06:59 PM   #2
Mihkus is offline Mihkus  Estonia
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Umm.. is your mute switched on? lol...
You added a bit over 2x sized to feedback?
You need 2x less resistance between feedback and out...


I might be wrong.
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Old 21st May 2013, 07:59 PM   #3
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Quote:
Originally Posted by navZ View Post
I have got LM3886 but its not getting unmute.
Please suggest Rm value for power supply of 18-0-18 dc.

When i disconnected Rm and left the pins untouched, there was only a little sound and that too even in max. input signal (full volume), indicating it to be in a mute condition.

I have seen datasheet and tried 22k, 10k, 5k,and 1.5k, but its still mute.

The rest schematics are according to figure1 of datasheet
CHANGES: replaced 22u with 47u and omitted Cm.
I would try with Rm 18k connected to V-. It should pass current over 0.5 mA for mute off, according to datasheet.
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Old 22nd May 2013, 06:14 AM   #4
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guys please help. I moved halfway across India to purchase two expensive lm3886 and now its not getting mute off. I placed ammeter in series to pin8, at Rm=5k, it showed 0.99 mA and at 1.5k it showed 1.42mA. But its not working either way. Accidently, I was holding sink with my hand and touched pin8, I heard a little DB gain in comparison to little sound at mute(pin 8 left opened n untouched) I have spend so much time and money that I m literally crying now Please help me!
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Old 22nd May 2013, 06:57 AM   #5
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Ahh, i wouldnt be crying over an amp chip. Tears are conductive...

I would redo the circuit exactly like it is in the datasheet and go from there.
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Old 22nd May 2013, 08:52 AM   #6
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are you sure its the only option? Bcoz its now same as datasheet. What you are saying is to redo the same thing and expect diff result. I can try it but by defination its insanity to expect diff result.

Isn't there any fault you can say about?
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Old 22nd May 2013, 10:25 AM   #7
AndrewT is offline AndrewT  Scotland
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the mute pin needs current to go to "unmute".
The datasheet details the range of currents that are acceptable and shows what a reduced current will do in attenuating the output.
Yes, a reduced current works as an attenuator. It is NOT a switch between mute and unmute.
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Old 22nd May 2013, 06:14 PM   #8
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Quote:
Originally Posted by navZ View Post
guys please help. I moved halfway across India to purchase two expensive lm3886 and now its not getting mute off. I placed ammeter in series to pin8, at Rm=5k, it showed 0.99 mA and at 1.5k it showed 1.42mA. But its not working either way. Accidently, I was holding sink with my hand and touched pin8, I heard a little DB gain in comparison to little sound at mute(pin 8 left opened n untouched) I have spend so much time and money that I m literally crying now Please help me!
I have no experience with LM3886 but looks like Rm current is too small for +-18V and 5k value. Check GND (pin 7) as well as power supply pins.
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Old 22nd May 2013, 06:54 PM   #9
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Are you connecting Rm between pin 8 and V(-) as shown in the data sheet? The chip is in mute mode with pin 8 disconnected, there needs to be at least (-).5mA flowing into pin 8 to un-mute.

Mike
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Old 22nd May 2013, 07:13 PM   #10
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Try a 3K6 resistor connected from the - volts to pin 8 of the LM3886 and see if it play music.
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