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Old 22nd May 2013, 08:25 PM   #11
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Quote:
Originally Posted by overall feedback View Post
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.
i have made more complex amps using tda7386, tda7294 perfectly working in once
and am not sure i am doing this ic correct. HOW FUNNY is that!

Moreover as i mentioned, i checked the current using multimeter in series from Rm to -V. At 5K it showed 0.99mA, but still no sound. At 1.5k, 1.4mA current was read, still the same.
Little worried if these are fake/damaged. But both ics showing same behaviour, i.e., at pin8 open, a little sound at full signal input whereas as soon its connected to -V via. 1.5K/5K/10K/22K, the little sound stops coming.

Here is the exact schematics I built.
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Last edited by navZ; 22nd May 2013 at 08:45 PM.
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Old 22nd May 2013, 08:56 PM   #12
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Does the non-inverting input have a dc-ground referance connection somehow? Schematic shows a single ground symbol which can't be right. There should be a separate ground path for: 1) input, feedback and pin 7 as a group, 2) power supply decoupling, and 3) speaker return and zobel. The power supply decoupling should be one small value ceramic disk (preferably COG/NPO) around 100nF with leads short as possible connected as close as possible to each supply pin and short path to common ground connection, and a medium size electrolytic (470uF to 1500uF) connected similarly with shortest possible leads.

Mike
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Old 22nd May 2013, 09:28 PM   #13
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Quote:
Originally Posted by Michael Bean View Post
Does the non-inverting input have a dc-ground referance connection somehow? Schematic shows a single ground symbol which can't be right. There should be a separate ground path for: 1) input, feedback and pin 7 as a group, 2) power supply decoupling, and 3) speaker return and zobel. The power supply decoupling should be one small value ceramic disk (preferably COG/NPO) around 100nF with leads short as possible connected as close as possible to each supply pin and short path to common ground connection, and a medium size electrolytic (470uF to 1500uF) connected similarly with shortest possible leads.

Mike
Oops, I had drawn so by mistake. Here is what i meant.

BTW, every diode is parallelly attached to 100nf. And i am quite sure this does not have any relation to the problem i am facing.

If i am missing something very important here, please at least draw me a rough sketch of modifications u recommend.
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Last edited by navZ; 22nd May 2013 at 09:34 PM.
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Old 22nd May 2013, 10:13 PM   #14
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Hi,
One thing that I noticed is that you are running both Lm3886 to the minimum permissible voltage allowed. I am running my at +/- 40 volts. I am not saying that running at +/- volts will not worked but it is a thought.
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Old 22nd May 2013, 11:11 PM   #15
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Does the non-inverting input have a dc-ground referance connection somehow?

Mike
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Old 22nd May 2013, 11:31 PM   #16
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You need a resistor from pin 10 (Vin+) to ground
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Old 23rd May 2013, 03:19 AM   #17
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Quote:
Originally Posted by tauro0221 View Post
Hi,
One thing that I noticed is that you are running both Lm3886 to the minimum permissible voltage allowed. I am running my at +/- 40 volts. I am not saying that running at +/- volts will not worked but it is a thought.
I didn't get your point. please be specific.
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Old 23rd May 2013, 03:24 AM   #18
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Originally Posted by volume knob View Post
You need a resistor from pin 10 (Vin+) to ground
are you sure that its responsible for no sound, because I m feeding input via. 100k analog controller
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Old 23rd May 2013, 04:19 AM   #19
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Once again, does the non-inverting (+)input have a dc-ground referance connection somehow? If there isn't a DC path for the input bias currents to follow, no, it won't work.

Mike
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Old 23rd May 2013, 06:15 AM   #20
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Quote:
Originally Posted by navZ View Post
are you sure that its responsible for no sound, because I m feeding input via. 100k analog controller
Maybe your input is attenuated, try with resistor to gnd and another source.
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