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Old 16th June 2011, 06:01 PM   #91
tomchr is offline tomchr  United States
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I started out without the capacitor across the bias spreader, but found that I could get a significant reduction in THD (I think 10x improvement, but I don't recall exact numbers) by adding the capacitor. So I put in 10 uF (I think it was) and left it at that. In his Power Amplifiers book, Bob Cordell includes a bit on why the capacitor is there and how it works. I forget the details, but the gist of it is that the bias spreader should be as close to a voltage source as possible at all relevant frequencies.

You can try to reduce the value of this cap to 1 uF or 100 nF to see if that gives you a good tradeoff between mute functionality and THD.

~Tom
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Old 16th August 2011, 05:36 PM   #92
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Are you mounting the diode stack on the heat sink for thermal compensation? Thx. smg
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Old 17th August 2011, 06:33 PM   #93
tomchr is offline tomchr  United States
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The STD03N, STD03P output devices are ThermalTrak (TM) devices. This means they have a built-in diode stack on the same die as the transistor itself. So not only is it mounted on the heat sink, it's on the same die attach paddle, and most likely on the same die.

Whether the diode is on the DAP or the die depends on the manufacturer. You'll have to consult with the relevant data sheets or app notes for that information.

~Tom
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Old 7th June 2012, 10:10 AM   #94
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Quote:
Originally Posted by shokoladas View Post
Hello,
I had to remove the capasitors between bases parallel after Vbe multiplier.Not because stability or something else,but because with the caps the mute control of lme49811 don't 'work correctly. To put in play mode was ok,but when i remove the voltage from sd pin the amp makes the ugly noise.The output goes negative with some ac noise and comes back slowly while my caps discharge. Current to sd pin 1.5ma. Tried sd pin to put to ground momentary as said in datasheet,but no sucsess. Looks like somehow these caps discharge through internal lme circuit after sd is put in mute mode.Without caps mute works fine.Changing from play mode to mute i can hear short click only few inches from tweeter.Anyone experienced this ? I am wondering how in lme49811 mute is implemented?
Hello, i have the same problem, my LME is to long for enter in PLAY mode, and in mute mode i have an "hmmmm" and négative DC on OUT ...

I have no idea for this problem ...
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Old 17th February 2014, 02:38 PM   #95
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Tom,

Is there any chance you can publish the PCB layout too, maybe on your webpage as mentioned earlier? It would be a great contribution.
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Old 18th February 2014, 07:49 AM   #96
tomchr is offline tomchr  United States
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I'm considering tidying up the layout and offering it for sale on my website, actually. It's in the queue behind a few other projects, though.

~Tom
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Old 18th February 2014, 07:50 AM   #97
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I see, thanks.
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Old 26th June 2014, 12:18 PM   #98
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Originally Posted by tomchr View Post
I'm considering tidying up the layout and offering it for sale on my website, actually. It's in the queue behind a few other projects, though.

~Tom
Tom,
Any success on the board? I'm seriously considering to test this driver for one of my tiny projects, so your work will help faster than my attempt to do it from scratch. PM me please if you have it done, or post the info here.

Thanks!
- Marat.
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Old 26th June 2014, 05:24 PM   #99
tomchr is offline tomchr  United States
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No... No progress on this, yet. Great progress elsewhere, though... Maybe I should up the priority on this. Let me see how much work is actually involved.

I'll definitely post a note here when I have a good layout and boards for sale.

~Tom
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Last edited by tomchr; 26th June 2014 at 05:27 PM.
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Old 29th June 2014, 09:57 PM   #100
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Well, I think it's time to employ one of my students then.
The question is: shall I share the heatsink with power transistors or not?

Pro: extra compact, no long conductors, no need in exotic HS (I'm in Russia), technologically elegant.
Con: no design like this yet, reason unknown. As it's a Class A device with constant quiescent current, it must not depend much on die temperature. Plus, the radiator that is sufficient for such an amp, won't heat or cool fast.

Opinions?..
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