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Old 20th December 2013, 09:29 PM   #1
Boscoe is offline Boscoe  United Kingdom
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Default A miniture LME49811 amp PCB.

I'm considering doing these as a group buy potentially with kits if there's enough interest. I wanted a nice compact high performance amplifier so I thought of the LME range. The amp uses the LME49811 and the ALF08NP16V5 for the power stage the keep things compact. I have PCBs to build and test (after christmas I can get some THD measurements). The boards measure just 55 x 22mm.

The smallest SM part is 0805.

So would people be interested in something like this? I think I could get the board coast down to about 7.5USD?

Here's some pics.

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Old 20th December 2013, 10:00 PM   #2
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Should be a great little project. I've used the LM4702 with lateral mosfets and it sounds very nice indeed.

Would suggest that these drivers do like some heat sinking -- so you might want to factor in some space so that a small hs can go on the driver chip.

If you panelize the boards -- i.e. -- design slots so they can be snapped apart -- you can bet a lot more square centimeters per pfennig. i know that my board house charges more for this, but it helps get unit costs down.
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Old 21st December 2013, 07:13 AM   #3
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Nice, work!

As the PCB design is already finished, it is too late to comment on it, so here some ideas if someone gets inspired to design something similar and even smaller.

Put the IC on the same heatsink as the mosfet. To the opposite edge on the PCB to the mosfet. Solder half the pins underside the PCB and half on top side.

Use IC and mosfet as the attachment to the heatsink.

Solution also solves a lot of other issues that otherwise need careful thinking. Such as the placement of the bias trimmer and compensation capacitor. Also the input and feedback component areas "automatically" become concentrated and super miniscule - which is nice...
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Old 21st December 2013, 07:51 AM   #4
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Isn't good idea to mount the LME49811 heat-sink close to C4 and C5 capacitors. That way the location of the components is not the best. Keep trying.

If you mount LME49811 to the output transistors heat-sink, the transistors in the input stage will be influenced by heat transistors from the output circuit of the amplifier. Even if a LME bias circuit will work properly - we believe this theory, basically is everything else - this mode of operation is not 100% beneficial. For this reason get in the other case: that the LME to use separate heat sink. But this case is not good because bias circuit not follow temperature output power transistors. So, we are two cases that we can not really choose. An alternative would be to use a external bias circuit instead of the trimmer. Try this.
For this reason, solutions kind LME49811 or other also I do not see viable, or in other words, let them. Use audio amplifiers schematic have only discrete components. It's much better that way.
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Old 21st December 2013, 08:53 AM   #5
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Isn't the VEB0 (ca. 6V) of Q1,2 too low for the task? After all, those diode-connected transistors could experience the full supply voltage.
For better efficiency (less heath) one should feed U1 from a higher voltage then the output stage.
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Old 21st December 2013, 09:28 AM   #6
Boscoe is offline Boscoe  United Kingdom
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Quote:
Originally Posted by palstanturhin View Post
Nice, work!

As the PCB design is already finished, it is too late to comment on it, so here some ideas if someone gets inspired to design something similar and even smaller.

Put the IC on the same heatsink as the mosfet. To the opposite edge on the PCB to the mosfet. Solder half the pins underside the PCB and half on top side.

Use IC and mosfet as the attachment to the heatsink.

Solution also solves a lot of other issues that otherwise need careful thinking. Such as the placement of the bias trimmer and compensation capacitor. Also the input and feedback component areas "automatically" become concentrated and super miniscule - which is nice...
Mounting the LME that way is not good practice. The board isn't thick enough, the height of the board is then determined by the IC and it's subjected to (most probably) a higher heat than one with it's own sink. And the design won't be much smaller.

Quote:
Originally Posted by donpetru View Post
Isn't good idea to mount the LME49811 heat-sink close to C4 and C5 capacitors. That way the location of the components is not the best. Keep trying.

If you mount LME49811 to the output transistors heat-sink, the transistors in the input stage will be influenced by heat transistors from the output circuit of the amplifier. Even if a LME bias circuit will work properly - we believe this theory, basically is everything else - this mode of operation is not 100% beneficial. For this reason get in the other case: that the LME to use separate heat sink. But this case is not good because bias circuit not follow temperature output power transistors. So, we are two cases that we can not really choose. An alternative would be to use a external bias circuit instead of the trimmer. Try this.
For this reason, solutions kind LME49811 or other also I do not see viable, or in other words, let them. Use audio amplifiers schematic have only discrete components. It's much better that way.
This amplifier is designed t work on 30V max rails so with the constant curretn of the LME this means it will dissipate just 0.9W. There is a gap behind the LME for a sheet of aluminium to fit which should be clipped on or, preferably, glued on with heat conductive glue. Estimated temp rise is just 20C, which is nothing.

And I wouldn't say discrete component designs are much better - most of the time they will be bettered in every aspect by integrated solutions.

Quote:
Originally Posted by franzm View Post
Isn't the VEB0 (ca. 6V) of Q1,2 too low for the task? After all, those diode-connected transistors could experience the full supply voltage.
For better efficiency (less heath) one should feed U1 from a higher voltage then the output stage.
Your correct however they will only be subjected to more than this when the power is applied so I'll see how they fair and replace with diodes is necessary.
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Old 3rd January 2014, 05:21 PM   #7
Boscoe is offline Boscoe  United Kingdom
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I have just done some testing and measuring the THD+N.

All at 8R 80KHz

1KHz 1W = 0.00198%
1KHz 10W = 0.00150%

10KHz 1W = 0.00346%
10KHz 10W = 0.00291%

20KHz 1W = 0.00988%
20KHz 10W = 0.00827%

I hope this creates some more interest?
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Old 3rd January 2014, 05:29 PM   #8
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I'm interested!

I think a pair of these inside of a 'dual differential loop' would be interesting.
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Old 4th January 2014, 08:22 AM   #9
Boscoe is offline Boscoe  United Kingdom
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Do you mean bridged Carl? I have boards if you want them.

Anyone else interested?
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Old 4th January 2014, 06:42 PM   #10
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Nope, Dual Differential (as in consuming two amplifiers) or what is often called a fully differential or a balanced amplifier. Nelson Pass would call it SUSY. Here is a good example. Your boards could be swapped for the LME49600 parts described here. PRODUCT HOW-TO: Differential line driver with excellent load drive | EE Times

And Twisted Pear has their Sympatico amplifer http://www.twistedpearaudio.com/docs..._schematic.pdf

Notice the feedback loops from amplifier outputs back to the differential inputs.
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Last edited by Carl_Huff; 4th January 2014 at 06:59 PM.
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