LME49811 Questions

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#21
Hi,
at 350Vce the graph shows 50mA @ 1s, 70mA @ 100ms and 100mA @ 10ms.

The worst case Ppk is when driving a reactive load and Vce ~supply rail voltage.
@ 90Vce the respective maximum single shot (non repeating) currents are 1.2A, 2.1A and 5A.
Using the 100ms value of 2.1A and de-rating for Tc=60degC we get
DrF=[150-60]/[150-25] = 0.72
The device can safely pass 0.72 * 2.1A @ 90Vce for less than 100ms when Tc<=60degC
Your 230W device is de-rated to 136W for those operating conditions.

4pair of these devices would be able to pass 6Apk @ 90Vce

In my opinion it is unlikely that 4pair could drive a reactive load of 8ohm reliably.
By my calculation a 60degree phase angle 8ohm load will draw ~8A @ 90Vce.
 
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#22
AndrewT - Thanks for the calculations/info! Since I'm planning to use this amp for a subwoofer, driving an 8 ohm load will not be an issue. Now, would it run cooler/more reliably if I used an extra pair or two transistors?

Also, for curiosity sake, would mosfets work in the place of BJTs or are they too capacitive for the LME to drive?
 
#25
I was wondering...
If, intended to a sub operation, multiplying the output devices above the SOA needs, couldn't allow to stay deeper into the linear current gain region of the devices, and get better current peaks.
(Taking care not to starve the drivers.)
The output impedance would be decreased too..
 
#26
bobodioulasso said:
Using 49811
Click to expand...

Interesting. I owned two RB1090's myself in the past (great amps, and I feel Rotel is highly under estimated in the "high-end world")

Funny thing is I walked the same road as you did. I also tracked down the RB1090 schematics and was plan to copy them 😀 But like you see in my other topic I changed the plan a bit and come up with some different ideas. Would u like to follow my path? 😀

Is there any topic where you discussed your project? I would love to read.

With kind regards,
Bas
 
#28
bobodioulasso said:
Finally i built it using LMA49810 + 5 pairs, erasing the pre drivers.
I use it for some weeks feeding my subs at 63 vots rails. I could feed it at 90v but do not feel the need anymore.
Click to expand...

Cool! any pics?

How do you like the sound so far?

The LME49810 is a terrific chip, and I am sure with this RB1090 output stage you have built an terrific amplifier.

With kind regards,
Bas

Ps: Sorry for going offtopic a bit.
 
#29
Basses are tremendous but i prefer my two F5 for mids and highs.
I have been taught the drivers are overkill and have a too high cob.
The highs might be enhanced vith a different device.
I will take some pics tomorow.
 
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#32
this is my schematic
 

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#33
bobodioulasso said:
this is my schematic
Click to expand...

Dear bobodioulasso,

Thank you. Two questions out of interest.

1: How you came up with the Ccomp of 20pF? Did you test this or was it just a thumb of the rule?

2: The Rsb of 2,2K seems high. Did you tried lower values? My feeling is that with Rsb of 2,2K the chip have to produce a lot of current and will drive mostly in class B. Combined with the relative high capacitance, this can cause distortion. Why not stick to the 1K value of Rotel?

With kind regards,
Bas
 
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