LME49811, bridged, DC servo, Thermaltrak

[Sebastiaan]

Dear All,

After reading a huge and great amount of resources according the LME devices and the ON thermaltrak. Many thanks to Panson, Douglas Self, Charles Hansen enz. for the inspiration.

I would like to share my implementation.

Please feel free to comment and/or criticize. Any help is always more then welcome

The idea behind this design is:

1: There should't be capacitors direct in series witth the signalflow. Hence the DC servo. The output of this servo should be fed to a protection system, that shuts's down the system by to much DC offset.

2: The amplifier should be a balanced bridged design. I love bridged designs.

3: Because it is an EF stage, the driver stage should be on a higher supply rails so it can fully saturate the end stage and distortion should be lower.

4: The common mode noise reduction on the input should be as good as possible, that is why the DC servo output function as a virtual ground as well

5: It should be able to supply good power at 4 ohm loads, hence the relative low power supply voltage for the end stage.

I look forward to your comments and/or suggestions

With kind regards,
Bas

http://img215.imageshack.us/img215/417/thermaltrak1.gif

[stinius]

Hi Sebastiaan

The link doesn't work.

Cheers

[Sebastiaan]

Originally Posted by stinius

Hi Sebastiaan

The link doesn't work.

Cheers

Dear Stinius,

I changed the link. It should work now It works here in the Netherlands

With kind regards,
Bas

[stinius]

Dear Bas
The link does not work here.
Maybe you could upload the picture here, not using an external link?

Cheers

[Sebastiaan]

Originally Posted by stinius

Dear Bas
The link does not work here.
Maybe you could upload the picture here, not using an external link?

Cheers

Sorry for that. Let's try this.

With kind regards,
Bas

[bobodioulasso]

Have you seen this?
GC SuperSymmetry

[Sebastiaan]

Originally Posted by bobodioulasso

Have you seen this?
GC SuperSymmetry

Dear bobodioulasso,

Thank you for the post. I know about the supersymmetry concept from Nelson Pass, but the topic you provide me is very interesting. I will read it carefully.

Thanks again.

With kind regards,
Bas

[bobodioulasso]

Why did you chose LME49811 and triple EF when 49810 and double EF make it simpler?

[Sebastiaan]

Originally Posted by bobodioulasso

Why did you chose LME49811 and triple EF when 49810 and double EF make it simpler?

Dear bobodioulasso,

I have good experiences with the LME49810, and indeed this chip is more practical (more current, clipping indicator enz.) But according to one of the former designers from National on this Forum the LME49811 should sound superior to the LME49810.

The extra driver stage in the LME49810 is low biased. With the LME49811 the designer has some more freedom and choices of driver stage bias and configuration.

With kind regards,
Bas

[stoc005]

One thing you can do is use the DC servo for DC offset protection. Since the opamp output never goes much over +/- 1v, use that fact to develop a signal that says your output has too much DC on it and use it to control something that "fixes" the problem. Say...shut down the amp. You don't show the PS for the opamp but I assume it is a bipolar supply. For current limiting I like Hall effect sensors. I also hate relays in series with the speaker. Use the Hall effect output to mute the audio input for a while to protect the amp.