LM3886, power caps, input resistors, mute, and Cm. - diyAudio
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Old 20th December 2007, 07:17 PM   #1
mudihan is offline mudihan  United States
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Default LM3886, power caps, input resistors, mute, and Cm.

Just got BrianGT's kit, and have a few questions:

On the amp board:
1) Would it be better to put R2 (signal to ground) before R1 (switch the positions)? Also, should the value of R2 be 10x of the value of the pot before it (i.e., 10k pot with 100k R2, followed by the original 1k R1)?

2) Would it be a good idea to put a 10000uf TS-UP +a 100uf FC + a 15uf Tantalum + a 0.1uf Film on each rail next to the chip. The TS-UP will further take care of ripple (after the 10000uf ones in the power supply section), the FC will charge faster, the tan will absorb low frequency variations (suggested by the datasheet), and the film will do the high frequency. --- I just have extra 10000uf TS-UP and 15uf Tans laying around.

3) Mute -- does this function degrade sound in any way? If it does, to disable it, would a 1/8w 10k resistor between Pin 8 and ground be enough (or will it get burned)?

4) The feedback caps Cm -- what is the lowest voltage requirement for those? I have 25v 47uf Silmic II laying around.

Many Thanks!
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Old 20th December 2007, 09:29 PM   #2
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Location: live in mountains
Cm is 100f/50V


Ci is 47f/50v


for the minimum rails voltage

tell us which toroids (18v,22v or 25v)you use and which speakers (4ohms or 8ohms )


http://www.chipamp.com/docs/lm3886-manual.pdf
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Old 21st December 2007, 01:32 AM   #3
mudihan is offline mudihan  United States
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I am using a 22VACx2 transformer, with 32vdc at the output of the power supply board. Driving 8ohm speakers (NHT acoustic suspension type) with around 86db sensitivities.

Is R2 (22k input to ground) really necessary if I put a 10k ladder-type stepped pot before R1?
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Old 21st December 2007, 09:23 AM   #4
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
Hi,
you must activate the mute pin. It won't amplify otherwise.
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regards Andrew T.
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