LM3886/3875 circuit with duo-beta - diyAudio
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Old 31st December 2006, 01:43 AM   #1
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Default LM3886/3875 circuit with duo-beta

I found the LM3886/3875 circuit with duo-beta at :
http://www.diyzone.net/articles/duo-beta.htm

Is it better than GC???
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Old 31st December 2006, 03:36 AM   #2
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Default circuit duo-beta??

Wont do much good in a single chip application, it will help you dial in the DC offset at idle, but wont be linear with gain.
The circuit will help set idle offset in a bridge parallel application, the circuit posted below has been used by myself with great results for large BPA amps.Click the image to open in full size.
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Old 31st December 2006, 04:46 AM   #3
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Halo0925 did i miss that or something? it looks like something to try. did you release it (with values) or is it something you would rather not?
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Old 31st December 2006, 04:53 AM   #4
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Default BPA

I did post it once a while back nobody had much interest. I use a very close circuit for my BPA300 that I use everyday with vantastic results.
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Old 31st December 2006, 05:03 AM   #5
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I would like to look in to that it looks very promising. opening up the sense inputs on the DRV was a pretty cool idea

can you point me to the thread.

sorry to OP if i have hijacked
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Old 31st December 2006, 05:22 AM   #6
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LM3875...
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Old 31st December 2006, 07:57 AM   #7
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Quote:
Is it better than GC???

It is a GC. The non-issue of dc offset has been solved. One may wish to further filter the bias voltage though.
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Old 31st December 2006, 08:00 AM   #8
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halo0925

Have you been able to measure or hear any improvement with the sense inputs connected? Or do they just allow the use of not very well matched resistors?
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Old 31st December 2006, 10:09 AM   #9
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the bridge parallel version...
sorry for my poor english
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Old 31st December 2006, 04:16 PM   #10
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Default DRV sense lines?

analog_se, No I did not notice any sonic improvements, its sounds almost identical to a singal non-inverted chip with no Ci cap except with much more power and control.
The idea was to better match each chip in the circuit without useing .1% or better resistors. My original circuit used 1% metal films and 2% carbon films for the NFB resistors and .15ohm 5% output resistors.
What I did notice was a drastic reduction in idle current per chip as much as 35% down from 80 - 90ma to 45 - 55ma, and the 1watt distortion was also drasticaly reduced, frequency response stayed the same from 15hz to 45khz,but with less role off after 22Khz, the amp gained great amounts of headroom.
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