LME49810/STD03 parallel pairs

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#21
Dxvideo said:
I am agree with you about the sound quality with more bias..
Just I'd like to try, but I am afraiding to destroy the diodes, because Sanken gives 2.5ma for the maximum Ibb level.. Anyway, I guess it would be better to keep it at 40mA bias (or 60 like yours)..
What about the sound quality of your amp? Have you ever compare it with a gainclone or a good discrete amp?
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You don't change the 2.5mA when you change bias current, you change the pot and measure the bias across the emitter resistors of the output devices to get 40mA through them (or 60mA).

As for the sound of my amp, see last post here:

http://www.elektor.com/forum/elektor-forums/recent-main-projects-and-articles/pax-(april-may-2008)/invitation-to-discussion.432667.lynkx?highlight=paX&pageStart=21

Edit: paste the whole link in your browser.
Jan Didden
 
#30
janneman said:
You don't change the 2.5mA when you change bias current, you change the pot and measure the bias across the emitter resistors of the output devices to get 40mA through them (or 60mA).
.....
Jan Didden
Click to expand...

May be it will be a bit late discovery! But are you sure about that? Means, how could you keep the 2.5mA while changing the pot value while it depends on this pots value!
HOW?
 
#31
Dxvideo said:
May be it will be a bit late discovery! But are you sure about that? Means, how could you keep the 2.5mA while changing the pot value while it depends on this pots value!
HOW?
Click to expand...

That is what I have been trying to say. You, as the designer, must make sure that the current is 2.5mA, for instance with a current source. That is the current where the thermal tracking is correct. Then you fiddle the pot to set the output stage bias current. But the diode current should be 2.5mA nominal.
Doesn't anybody read data sheets anymore???

jd
 
#32
Ok... So you (or Sanken) say if I set the diode current around 2,5mA the bias should be ~40mA but I can still adjust it an exact value while the diode current is still ~2,5mA!
Is it?
By the way, I was already read the manual (both STD and SAP) however this point is not good explained..
Thx.
 
#34
minhtriet said:
Dear All!
I want to buy an amplifier with LME489xx driver one or two pair SAP15s. What LME chip I will choose? LME49810 or 49811?
Thanks.
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Dxvideo said:
I am currently working on a project with SAP15s and LME49811. I think 49811 is the best solution for SAPs. Because they already have a biasing systems and do not need Vbe multipliers. So if you consider 49810 and 49830 has bias pins then 49811 (or LM4702) is the best for SAPs. Another point is 49811 has Class A driving stages..
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I don't agree.
The 811 is designed with an output stage that suits low current demand.
The 810 is designed for about seven times as much current demand and better suits a two stage (Darlington) output pair.
I think the 811 needs a three stage output pair for anything that demands output current, i.e. any speaker rated at less than 8ohms.
 
#36
Hi,
work back from the valid audio signal maximum peak transient current.

Let's for sake of this example assume +-50Vdc supplies and an 8ohm speaker.
Peak current ~[50-3] / 8 / 0.35 ~16.8Apk.
If you assume 4 to 8ohms speakers then the transient maximum exceeds 33Apk.

There is some evidence that the 0.35 factor gives too low a result for some music types and some speaker types. I have seen some claiming 0.2 as a worst case factor.
 
#39
This is about needing predrivers with the lme49811 when driving 4 ohm loads. If you pick a driver with a high hFE you won't need a predriver. You will need multiple output transistors to keep within the soa and the will need decent hFE for the current driven.
 
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