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Old 18th May 2012, 11:44 AM   #11
KSTR is offline KSTR  Germany
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Ouroboros, could you check the open-loop gain/phase?

Run an AC analysis, plot Vout / (Vin+ - Vin-), that is, chip output divided by input pin differential.
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Old 18th May 2012, 11:44 AM   #12
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Just tried it now with the LM3886 model. Distortion with this at gain x21, Vin 1V 1kHz, load 4R give stupidly low figures for THD. Don't know why the 3875 simulates ok but not the 3886.
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Old 18th May 2012, 11:51 AM   #13
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Default TI LM3875 SPICE model

TI LM3875 Spice model (TINA)

Hopefully the O/L Bode plot should be attached.
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File Type: jpg LM3875 Bode.jpg (62.6 KB, 570 views)
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Old 18th May 2012, 12:04 PM   #14
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Default TI LM3886 SPICE Bode plot (TINA)

They seem to have cocked up the LM3886 model though...
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File Type: jpg LM3886 bode.jpg (97.1 KB, 559 views)
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Old 18th May 2012, 12:33 PM   #15
KSTR is offline KSTR  Germany
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^^ Thanks.

I contacted TI, now that we know that TINA also shows the problem.
Faulty SPICE model of LM3886? - Audio Amplifiers Forum - Audio Amplifiers - TI E2E Community
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Old 18th May 2012, 01:10 PM   #16
rumors is offline rumors  Italy
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Quote:
Originally Posted by rumors View Post
With model "PSpice" Work and AC analysis set:

http://www.diyaudio.com/forums/attac...1&d=1337346278
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Old 18th May 2012, 01:29 PM   #17
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Are you all sure that the MUTE behaviour is wrong? The data sheet says that if you leave the MUTE pin o/c or pulled to V+ the 3886 is enabled. To mute the amp you pull >1mA out of the MUTE pin (by connecting a resistor to 0V or V-)
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Old 18th May 2012, 02:02 PM   #18
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Oh-Oh, my fault. It appears that the MUTE function is muted when the pin is floating, and un-muted when >1mA is taken out of the pin. This seems strange, as if it were the other way round you could apply an automatic mute at power-up by connecting a large-value cap between the MUTE pin and 0V
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Old 18th May 2012, 02:06 PM   #19
KSTR is offline KSTR  Germany
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"Mute Function: The muting function of the LM3886 allows
the user to mute the music going into the amplifier by draw-
ing less than 0.5 mA out of pin 8 of the device. This is
accomplished as shown in the Typical Application Circuit
where the resistor RM is chosen with reference to your
negative supply voltage and is used in conjuction with a
switch. The switch (when opened) cuts off the current flow
from pin 8 to V−
, thus placing the LM3886 into mute mode."


Also the function is clear from the internal schematic. The main diff-amp is OFF when the MUTE pin is left open, while the auxiliary diff-amp is ON.

EDIT: Cross-post, I see.

In fact I like the MUTE and STANDBY features of the TDA7294 much better than the slightly akward MUTE of the LM3886.

Last edited by KSTR; 18th May 2012 at 02:08 PM.
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Old 18th May 2012, 03:15 PM   #20
Bill_P is offline Bill_P  United States
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Quote:
Originally Posted by KSTR View Post
see my take on a correct bode plot estimation here.
Would you post the .asc file containing your LM3886 model?
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