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Chip Amps Amplifiers based on integrated circuits

Composite amplifier: LM3886 + LME49710
Composite amplifier: LM3886 + LME49710
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Old 5th March 2019, 05:05 AM   #51
tomchr is online now tomchr  Canada
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Quote:
Originally Posted by jeanlemotan View Post
Sweet. Thanks.

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Originally Posted by jeanlemotan View Post
Here is the PSU I intend to use with this amp:
I suggest routing VCC/VEE as pours rather than traces.

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Originally Posted by Grendel321 View Post
Tom, as you said composite amps are difficult to stabilise and my guess is that you would have had to compromise on the bandwidth to maintain adequate stability margins.
There are basically three fundamental ways of stabilizing a feedback loop:
  • Reduce loop gain
  • Dominant pole compensation
  • Phase lead/lag compensation
I use all three in the Modulus-86.

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Originally Posted by Grendel321 View Post
Someone with your knowledge could easily design a discrete power amp with impressive specs
Thank you. I'm glad you think so. I may create such a design in the future. Time will tell.

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Originally Posted by Grendel321 View Post
what made you select the lm3886 composite high power solution path?
Convenience. The LM3886 is well recognized in the DIY community and can be teased into providing world class performance if used within a composite loop. It's very DIY friendly - basically plug-n-play. There's no bias to adjust. No over-current protection loops to go unstable. No drama around output devices. It just works.

That said, the LM3886 is not without quirks. I cover some of them in my Taming the LM3886 series. I need to get the remainder onto my website before they disappear out of my brain.

Unfortunately, the LM3886 also comes with a bit of "chipamp stigma". That's really unfortunate as it can really sing if treated right. And, honestly, the transistors don't know whether they're inside an IC or inside a discrete package.

Tom
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Old 5th March 2019, 05:49 AM   #52
kokoriantz is offline kokoriantz  Lebanon
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May be you are not a knowledge with documents AN-1192 . As you dealing for educational purpose , I advise to learn also using CFA op amps . The AD8008 is very simple . You can tie it to the +input of the open loop 3886 with -input grounded and the LM3886 gets transformed into CFA with the AD8008 inputs .
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Old 5th March 2019, 05:58 AM   #53
kokoriantz is offline kokoriantz  Lebanon
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example to start with.
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File Type: jpg ad8008,3886E.JPG (38.1 KB, 388 views)
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Old 5th March 2019, 06:20 AM   #54
RobSoet is offline RobSoet
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Composite amplifier: LM3886 + LME49710
Hi Jean,
A few thoughts I had while following your project... . With the necessary disclaimers. I'm not an expert... .

When using a voltage divider to make sure the opamp clips before the 3886, you could also consider a slower opamp like the opa1688, which has a similar slew rate as the lm3886. This might simplify the stabillity question. I's be interested to understand the impact on noise performance of the voltage divider.

for the input you could consider an opa1632. Downstream of the opa1632 you can built identical bridge halves.

With the 1632, you have an input stage. You could make this clip before the lm3886 clips by putting anti parrallel diodes between the two outputs. Again, I'd be interested to understand what the impact on THD and noise would be vs the voltage divider.

Attached a Tina spice sketch...

Best regards,
Rob
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File Type: zip opa1632_3886_PARRALLEL.zip (13.1 KB, 24 views)
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Old 5th March 2019, 08:08 AM   #55
jeanlemotan is offline jeanlemotan
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Quote:
Originally Posted by tomchr View Post
I suggest routing VCC/VEE as pours rather than traces.
Done! I keep forgetting to use pours... I did the same for the new amp PCB btw.
Thanks for the advice.
Quote:
Originally Posted by tomchr View Post
Convenience. The LM3886 is well recognized in the DIY community and can be teased into providing world class performance if used within a composite loop. It's very DIY friendly - basically plug-n-play. There's no bias to adjust. No over-current protection loops to go unstable. No drama around output devices. It just works.
I thought about doing a discreet amp at first but after reading on this forum the challenges of doing a good amp with a LM3886 I imagined it cannot be easier going discreet.
Stability, protections, PCB design are full of traps. Unless one is doing discreet for the learning experience of course.
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Old 26th March 2019, 01:10 PM   #56
zarandok is offline zarandok  Austria
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Hi for all,
thats my small project, perhaps can I give some good /or bad.../ ideas....
Attached Images
File Type: jpg 3D_1 - C-AMP 1.0.JPG (83.6 KB, 282 views)
File Type: jpg 3D_2 - C-AMP 1.0.JPG (37.9 KB, 278 views)
File Type: jpg SoftStart_3D_1.JPG (71.2 KB, 277 views)
Attached Files
File Type: zip Simulation.zip (320.1 KB, 12 views)
File Type: pdf Schematic - C-AMP 1.0.pdf (48.8 KB, 63 views)
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Old 26th March 2019, 02:20 PM   #57
anti is offline anti  Slovakia
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The C13 value seems to be missing on your schem.
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Old 26th March 2019, 03:22 PM   #58
zarandok is offline zarandok  Austria
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At first I'll try to leave it...
But more interesting is the C7-R13 (470p-5k) feedback. After simulation with this values can I get the best performance.
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Last edited by zarandok; 26th March 2019 at 03:25 PM.
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Old 26th March 2019, 08:24 PM   #59
RobSoet is offline RobSoet
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Composite amplifier: LM3886 + LME49710
Been thinking along the same lines. Take the input from a bppbp, set fixed gain in the last stage instead of a pot. I m wondering, with a cap. Catching dc at the input, if you add some trimming on one of the opamp voltage regulators, would it be possible to trim away dc offset reliably long term and drop the dc servo?

Also wondering whether something like opa1612 can take this even further, or would it just be a waste of money?
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Old 27th March 2019, 12:06 PM   #60
zarandok is offline zarandok  Austria
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The game is about in our case I think to find a sensible balance between quality and stability... In one hand we can simulate some parameters of the the circuit and make some clever ideas, on the other hand we must measure the real behaviour and correct it if needed. Tom has advanced experiences in this...
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