LM3886/3875 circuit with duo-beta

xiaoao360 · 31st December 2006, 12:43 AM

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

Is it better than GC???

halo0925 · 31st December 2006, 02:36 AM

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.

neutron7 · 31st December 2006, 03:46 AM

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?

halo0925 · 31st December 2006, 03:53 AM

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.

neutron7 · 31st December 2006, 04:03 AM

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

xiaoao360 · 31st December 2006, 04:22 AM

LM3875...

analog_sa · 31st December 2006, 06:57 AM

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.

analog_sa · 31st December 2006, 07:00 AM

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?

xiaoao360 · 31st December 2006, 09:09 AM

the bridge parallel version...
sorry for my poor english

halo0925 · 31st December 2006, 03:16 PM

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.

31st December 2006, 02:36 AM	#2
halo0925 diyAudio Member Join Date: Aug 2006	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.

31st December 2006, 03:53 AM	#4
halo0925 diyAudio Member Join Date: Aug 2006	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.

31st December 2006, 03:16 PM	#10
halo0925 diyAudio Member Join Date: Aug 2006	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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31st December 2006, 03:46 AM	#3
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	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?

31st December 2006, 04:03 AM	#5
neutron7 diyAudio Member Join Date: Dec 2003 Location: Toronto Canada	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

31st December 2006, 07:00 AM	#8
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	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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