LME49810 with 2sa1943 and 2sc5200

[xeclipse]

Hi guys,
I am looking forward to build an amp using these devices from scratch.I've done a lot of research thats why i settled for those.
I need a mono amp,200w into 8 ohm load.
I have several questions:
-with a supply of +/-50 volts,how many pairs of output devices will i need?
-which output topology to use (efficient and simple).I envy QSC rmx 850 output topology.
-with such power,will drivers be really needed?
I already have the power supply with 10,000 uF per rail and more than enough heat sink.
A working schematic with the pcb layout will greatly help. I am looking for simplicity since its my first solid state amp,those are the reasons that made me go for the lme chip.
I'll also appreciate tips on preventing thermal runaway.

Regards Xeclipse.

 

[nigelwright7557]

>-with a supply of +/-50 volts,how many pairs of output devices will i need?
2 pairs should cope OK.

>-which output topology to use (efficient and simple).I envy QSC rmx 850 >output topology.
You will need drivers after the VAS.
>-with such power,will drivers be really needed?
Yes.

>I'll also appreciate tips on preventing thermal runaway.
Use a Vbe multiplier with the transistor on the heatsink or glued on an output transistor is even better.

 

[xeclipse]

Thanks for the info Nigelwright7557.Some of that are in the chip's datasheet.
I still got a few questions,will parallel outputs go well with the chip?I noticed that in the datasheet the outputs are in emiter follower topology.
What do i look for in a Vbe multiplyer transistor?Is there any you recommend?
Regards.

 

[east electronics]

check this

here is a schematic

 

[andrewlebon]

hi xeclipse
greetings want to make simplest class ab amp r u interested
e mail me
thanking you
andrew lebon

 

[east electronics]

yes of course ... even the John fisher amplifier is somewere arround here .....

 

[AndrewT]

+-50Vdc for a supply cannot give 200W into 8r0.
It can give 100W into 8r0 and/or 200W into 4r0.
If you need 200W into 8r0 then increase the supply to +-65Vdc.

Your 1943/5200 better suit the lower voltage (+-50Vdc) than the higher voltage.

1pair for 100W into 8ohm (35+35Vac)
2pair for 200W into 4ohm (35+35Vac)
3pair for 200W into 8ohm (45+45Vac)
provided you keep them cool.

 

[homemodder]

Sakis whos the designer of that amp, 22ohms for base stoppers to the output transistors ???? I think no good.

 

[xeclipse]

Thanks for the schematic Sakis,i really appreciate it.

 

[xeclipse]

Hi Homemodder,i also noticed that.I don't think the resistors are even necessary.
Hi Andrew T,what's the expected power output using 2 pairs with the same supply into 4 ohms?I got sufficient cooling.
Regards

 

[nigelwright7557]

Thanks for the info Nigelwright7557.Some of that are in the chip's datasheet.
I still got a few questions,will parallel outputs go well with the chip?I noticed that in the datasheet the outputs are in emiter follower topology.
What do i look for in a Vbe multiplyer transistor?Is there any you recommend?
Regards.

I use MPSA42 for Vbe multiplier.

 

[AndrewT]

X,
expect roughly double the maximum power output when changing from 1pair into 8r0 to 3pair into 4r0.

If it only increases maximum power by 50%, then throw the amplifier in the bin.
If it increases the power by >=75% then keep it but work on it until it's current delivery is improved until the power increase is >80%.

 

[xeclipse]

thanks Andrew T.
I found a thread about insulating and fixing of power transistors and it got me thinking,is it necessary to insulate output trans if they are in the 'QSC topology'?I mean,all the collectors are grounded anyway.
Regards