[LM3886] Best resistor value for mute ? - Page 3 - diyAudio
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Old 12th November 2005, 10:44 PM   #21
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Just made my LM4780 amp run tonight, and it has absolutely silent turn-on and off transcients. I measured the transcients with a DMM : there is a 60mV peak when turning off, and nothing when turning on, so there is nothing audible.

They say the mute resistor should be 10k, I used 9.1k so I'm sure the mute pin will draw its 0.5mA from the -V rail

I assume those 0.5mA are just supervised by a mute circuit, and changing the resistor value won't affect it as long as this current is just "witnessing" that the amp shouldn't be muted.

Maybe the transcients one may experience are due to the caps on the feedback network ? They may store some energy and send it back when the circuit is powering down ?
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Old 12th November 2005, 11:00 PM   #22
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Quote:
Originally posted by youyoung21147
Maybe the transcients one may experience are due to the caps on the feedback network ? They may store some energy and send it back when the circuit is powering down ?
I don't think so.
I said that the LM3886/4780 doesn't need the muting cap, and it sure doesn't, as you concluded too.
P-A has extra op-amps on board (which can generate turn-on transients), and he probably doesn't have experience with these LM chips alone.
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Old 14th November 2005, 09:05 AM   #23
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Hey Guys.


I lost this weekend trying to find the right resistor value for the mute!

After trying a few resistors I tried the -Vcc connected directly to the mute pin
And yes, this is another step forward in the LM3886 implementation

This chip is playing like this since Saturday and, till now, it's running fantastic.


( I think that the LM3886 have some sort of protection that allow him to run like this )



Setup:
1x LM3886 p/ channel
20.000uF p/ rail
1200VA trafo ( [-Vcc] + [+Vcc] = 94V )
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Old 14th November 2005, 12:49 PM   #24
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What value did you prefer in the end?
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Old 14th November 2005, 02:02 PM   #25
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Short circuit so it seems

I think 10k is good if you don't have any special requirements.
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Old 14th November 2005, 03:12 PM   #26
XELB is offline XELB  Portugal
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Quote:
Short circuit so it seems
There's no short circuit

The LM3886 must have some sort of protection and the mute stays OFF


With this implementation the current inside the chip doesn't depend of the mute resistor.



Give it a try, wait 30m/1H to heat the chip and then listen




BTW, the LM3886 runs much better when is hot!
The right(not to big and not to small) heatsink could improve sound dynamics...
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Old 14th November 2005, 08:14 PM   #27
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Quote:
Originally posted by XELB
There's no short circuit
There must be an internal protection for guys like you.

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Old 14th November 2005, 09:38 PM   #28
XELB is offline XELB  Portugal
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Quote:
Originally posted by carlosfm


There must be an internal protection for guys like you.


And it plays very well, just like guys like me like
It plays 3xLike LOL



Why don't you try
It's safe, but if you are affraid of burning one LM3886, I have an extra chip
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Old 14th November 2005, 10:07 PM   #29
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XELB, could you measure the current you have through the MUTE pin and report back? What supply voltage do you have?
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Old 14th November 2005, 10:34 PM   #30
XELB is offline XELB  Portugal
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As I told before, the LM3886 is running at max. specs |+V|+|-V| = 94V


Are you affraid of testing without the resistor ?

heheheheheh
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