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Old 4th June 2010, 11:39 PM   #81
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Hi Tom,

Under what operating condition you measured ten fold THD difference?

Panson
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Old 9th June 2010, 06:31 PM   #82
tomchr is offline tomchr  United States
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Quote:
Originally Posted by panson_hk View Post
Under what operating condition you measured ten fold THD difference?
I don't remember exactly. I was running on a +/-25 V supply that could supply 1 A, so the output power would have been limited to about 4 W RMS into 8 ohms. I suspect this was the condition I used for the test. Could have been 1 W, though. I'm fairly certain I was measuring at 1 kHz.

~Tom
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Old 9th June 2010, 11:44 PM   #83
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Thank you Tom.
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Old 11th June 2010, 06:05 AM   #84
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Default Square wave test with cap load

Here are some waveforms of square-wave with capacitive load. Output level is 20 Vpp. An output coil with 10R damping resistor is employed.
Attached Images
File Type: jpg Square Wave 1 kHz 0p1u+8R.JPG (81.9 KB, 1242 views)
File Type: jpg Square Wave 1 kHz 2u+8R.JPG (87.2 KB, 1207 views)
File Type: jpg Square Wave 10 kHz 0p1u+8R.JPG (86.6 KB, 1185 views)
File Type: jpg Square Wave 10 kHz 2u+8R.JPG (98.8 KB, 1147 views)
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Old 11th June 2010, 09:09 PM   #85
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Quote:
Originally Posted by panson_hk View Post
Here are some waveforms of square-wave with capacitive load. Output level is 20 Vpp. An output coil with 10R damping resistor is employed.
Dear Panson,

Thanks for sharing.

Do you also have a 20KHz Square-wave plot on a pure resistive load? I think you should slightly increase the miller compensation to avoid the overshoot.

Of course, more important, we are all curious how does it sound?

With kind regards,
Bas
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Old 13th June 2010, 10:20 PM   #86
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Quote:
Originally Posted by Sebastiaan View Post

Do you also have a 20KHz Square-wave plot on a pure resistive load? I think you should slightly increase the miller compensation to avoid the overshoot.

Of course, more important, we are all curious how does it sound?
Hi Bas,

Here is 20 kHz square wave (20 Vpp) without cap load. I currently use 32 pF. I will assemble another board to make a stereo amp for listening.

Panson
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File Type: jpg Square Wave 20 kHz 8R.JPG (69.8 KB, 1066 views)
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Old 18th November 2010, 04:00 AM   #87
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Originally Posted by Sebastiaan View Post
Thank you Tom for this good explanation. It makes me understand the function of the cap. Did you also experiment with different values?
Hey, 'bas, apropos of the discussion over here I noticed your early schematic shows 100nF || 47uF and later ones 100nF || 22uF. Did you happen to wind up with any comparative data between the two?
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Old 22nd December 2010, 06:13 PM   #88
tomchr is offline tomchr  United States
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Default Final schematics

Folks,

I finally got around to updating the schematic with a few component changes and some annotation. See attached.

The amp has been playing quite happily for months now. The design seems solid. Even after some 8~9 months in service, the bias is still rock solid at 41 mV for the left channel, 42 mV for the right (across 440 mOhm - target value: 40 mV). Given how finicky it is to adjust, my bet is that the bias hasn't moved more than 1 mV from its initial value. That corresponds to 2 mA (or 2 %).

~Tom
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File Type: pdf LME49811amp_TC20101222.pdf (24.8 KB, 842 views)

Last edited by tomchr; 22nd December 2010 at 06:22 PM.
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Old 15th June 2011, 06:16 AM   #89
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Hello,
I had to remove the capasitors between bases parallel after Vbe multiplier.Not because stability or something else,but because with the caps the mute control of lme49811 don't 'work correctly. To put in play mode was ok,but when i remove the voltage from sd pin the amp makes the ugly noise.The output goes negative with some ac noise and comes back slowly while my caps discharge. Current to sd pin 1.5ma. Tried sd pin to put to ground momentary as said in datasheet,but no sucsess. Looks like somehow these caps discharge through internal lme circuit after sd is put in mute mode.Without caps mute works fine.Changing from play mode to mute i can hear short click only few inches from tweeter.Anyone experienced this ? I am wondering how in lme49811 mute is implemented?
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Old 15th June 2011, 07:06 PM   #90
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Had to put back the capasitors because the performance was degraded. But the mute still mistery not solved.
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