My "audiophile" LM3886 approach

mauropenasa · 31st March 2005, 02:52 PM

my modest contribution to this forum...

Mauro Penasa

Giaime · 31st March 2005, 03:20 PM

It looks good! But I'm not sure about the use of an opamp in front of the LM3886, many people there believe in a "less parts better" approach towards Gainclones. I don't know...

And what's that circuit (the first one on page 2)? Is it a speaker protection or a startup delay?

And where do you get LM3886 in Italy? How much you pay?

Joseph K · 31st March 2005, 03:27 PM

Hi maupenas!

Very nice! Thorsten would like it..
But you have overtaken us! It's ages that my friend pushes me to realize this concept! Though he wants it a bit modified, so as to get "constant power" drive, instead of current drive.

For me, the question is: how this all react with Your speaker? [Mine is a two-way bass reflex]
Did you measure the actual Rout? Stability?

Ciao, George

Yoghourt · 31st March 2005, 03:40 PM

Hello,

I've just glanced at your design, so my question is surely silly. How does your speaker protection cope with negative DC offset?

analog_sa · 31st March 2005, 03:55 PM

A very unusual design. The 3886 is just a power booster for the 318. I wonder how it sounds compared to the more traditional approach. Any problems with stability?

Joseph K · 31st March 2005, 06:34 PM

No, it's not a power booster..

Doh, I was not looking close enough at the first glance - so I take it back - it IS a kind of a power booster.. though a tricky one. [it's not a unity gain buffer on the output..]

At first I was only looking at the 3886 circuit. My note was referring to that. I still would like to try one day.

analog_sa · 31st March 2005, 06:49 PM

Ehm, what would you call it? It's got a unity gain and falls under the 318 feedback loop.

Joseph K · 31st March 2005, 06:57 PM

sorry, analog_sa, as you see, in the meantime also I have recognized it

The opamp controls the output current..

Joseph K · 31st March 2005, 07:05 PM

So as to be clear: the LM3886 is a voltage controlled bipolar current source in this configuration. It does not have any voltage gain; it has an input voltage/ output current transfer characteristic - which is, in this case, is 100.

And it is stable in this config.

analog_sa · 31st March 2005, 07:07 PM

Quote:

And it is stable in this config.

I am sure it is. What about the entire amp? I guess it's fine with the compensation caps.

31st March 2005, 03:40 PM	#4
Yoghourt diyAudio Member Join Date: Jun 2004 Location: Alpes	Hello, I've just glanced at your design, so my question is surely silly. How does your speaker protection cope with negative DC offset? __________________ Dzharis: raaaaaah lovelyyyy!

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31st March 2005, 03:20 PM	#2
Giaime diyAudio Member Join Date: Oct 2004	It looks good! But I'm not sure about the use of an opamp in front of the LM3886, many people there believe in a "less parts better" approach towards Gainclones. I don't know... And what's that circuit (the first one on page 2)? Is it a speaker protection or a startup delay? And where do you get LM3886 in Italy? How much you pay?

31st March 2005, 03:27 PM	#3
Joseph K diyAudio Member Join Date: Dec 2004 Location: gran sasso	Hi maupenas! Very nice! Thorsten would like it.. But you have overtaken us! It's ages that my friend pushes me to realize this concept! Though he wants it a bit modified, so as to get "constant power" drive, instead of current drive. For me, the question is: how this all react with Your speaker? [Mine is a two-way bass reflex] Did you measure the actual Rout? Stability? Ciao, George

31st March 2005, 03:55 PM	#5
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	A very unusual design. The 3886 is just a power booster for the 318. I wonder how it sounds compared to the more traditional approach. Any problems with stability?

31st March 2005, 06:34 PM	#6
Joseph K diyAudio Member Join Date: Dec 2004 Location: gran sasso	No, it's not a power booster.. Doh, I was not looking close enough at the first glance - so I take it back - it IS a kind of a power booster.. though a tricky one. [it's not a unity gain buffer on the output..] At first I was only looking at the 3886 circuit. My note was referring to that. I still would like to try one day.

31st March 2005, 06:49 PM	#7
analog_sa diyAudio Member Join Date: Aug 2002 Location: Sofia	Ehm, what would you call it? It's got a unity gain and falls under the 318 feedback loop.

31st March 2005, 06:57 PM	#8
Joseph K diyAudio Member Join Date: Dec 2004 Location: gran sasso	sorry, analog_sa, as you see, in the meantime also I have recognized it The opamp controls the output current..

31st March 2005, 07:05 PM	#9
Joseph K diyAudio Member Join Date: Dec 2004 Location: gran sasso	So as to be clear: the LM3886 is a voltage controlled bipolar current source in this configuration. It does not have any voltage gain; it has an input voltage/ output current transfer characteristic - which is, in this case, is 100. And it is stable in this config.