OPA541AP Subwoofer amp

[Alcaid]

Hi!

Can someone help me to build a subwoofer amp with the OPA541 chip. If it is supposed to be 4ohm stable, do I need to do a parallell setup, or maybe a bridged parallell?

How many watts will it then push out?

Anyone got schematics for these setups with the OPA541?

OPA541 or OPA549 for a sub amp? (or another IC is better?)

Thanks for any answers!

 

[Alcaid]

Can someone help?

Anyone who have parallelled the OPA541?

How many watts can it give into 4ohm?

 

[Mad_K]

build something like this.
you can use the opa541am/ap, just put a link from after Rout on each chip back to pin 1/8 on the opa541am/ap. it will give you 200W in 4 ohms

http://www.national.com/an/AN/AN-1192.pdf

edit: you can also use lm3875/3886/opa549

 

[Alcaid]

Thank you for the answer

Is it really this simple? No other parts, except those in the power supply?

How can I figure out what trafo to use when it's used on a 4 ohm subwoofer? What secondary voltages, and what VA rating is needed?

I plan on buying ToroidTM trafo, I see you use them Mad_K, are they any good?

 

[Mad_K]

yes it's that simple

buy the 600VA 2*24VAC one (elfa nr 56-139-30). they are very good. you have to use a softstart circuit with a trafo of this size.

a pair of rifa peh200 will also be nice (for example elfa nr 67-661-33)

 

[Alcaid]

Isn't 600VA a bit overkill? (and budget killer )

How do I build a softstart circuit?

When you say 200W, do you mean peak or RMS?

Thanks for helping

 

[Alcaid]

Sorry for all the stupid questions, but here's another one:

Is the power supply on the link under good for my project? (With the two Rifas near the chips).

http://www.euronet.nl/~mgw/diy/amps/geenkloon_powersupply_schema.gif

Anyone got a schematic for a powersupply to recommend?

 

[Mad_K]

skip the 0,1uF caps, use regular high-powered bridge rectifier (~25A) and use the peh200 instead of c1/2. on a second thought -use the 0,1uF caps directly on the chip between v+/v- and gnd.


here's some light reading: http://www.tnt-audio.com/clinica/ssps1_e.html

 

[Alcaid]

Thanks for that link!

Answered all my questions concerning power supplies.

 

[JojoD818]

you can use the opa541am/ap, just put a link from after Rout on each chip back to pin 1/8 on the opa541am/ap. it will give you 200W in 4 ohms

does that mean that the pin 8 of the 2 541s in a parallel mode are tied together?

Thanks,
JojoD

 

[Mad_K]

does that mean that the pin 8 of the 2 541s in a parallel mode are tied together?

Thanks,
JojoD

nix

 

[JojoD818]

Mad_K,

I feel so stupid, but can you please be more specific? A schematic will be appreciated.

JojoD

 

[Alcaid]

He means a link from after 1st Rout to 1st chip's pin 8 and a link from after 2nd Rout to 2nd chip's pin 8.

In this case after UPPER Rout to U1 and after LOWER Rout to U2.

 

[JojoD818]

In that case, I am right then. Because the 2 after Rout are tied together and so will the 2 pin 8s of the opa541.

JojoD

 

[JojoD818]

Is this correct?

JojoD

 

[JojoD818]

Sorry, too quick on the trigger...

JojoD

 

[Alcaid]

I see from the datasheets that the OPA541 delievers 5A continous and can handle +-40V on the supply. The OPA549 can deliever 8A, but it can only handle +-30V on the supply. From http://focus.ti.com/lit/an/sboa082/sboa082.pdf you can also see that OPA549 has lower THD+N.

How can i calculate how many watt they will deliever at 2ohm, 4ohm or 8ohm? V^2/R=W, but how do I find out how many volt it can deliever. It can't deliever as much as the supply, or am I wrong?

Is current calculated V/R=A ?

I want to find RMS values. Is it then (V/root2)/R=W ?

 

[Alcaid]

How do you calculate the efficiency of the heatsink needed? Then you would have to calculate the heat dissipated by the IC, how to do that?

Lots of questions in this neewb head.

 

[Mad_K]

I see from the datasheets that the OPA541 delievers 5A continous and can handle +-40V on the supply. The OPA549 can deliever 8A, but it can only handle +-30V on the supply. From http://focus.ti.com/lit/an/sboa082/sboa082.pdf you can also see that OPA549 has lower THD+N.

How can i calculate how many watt they will deliever at 2ohm, 4ohm or 8ohm? V^2/R=W, but how do I find out how many volt it can deliever. It can't deliever as much as the supply, or am I wrong?

Is current calculated V/R=A ?

I want to find RMS values. Is it then (V/root2)/R=W ?

from opa541 datasheet "Voltage swing=Vs-5,5 @Iout=5A"

The wattage @4/2 are normally limited by current P=((I*root2)^2)*R. R=8/4/2..

Ipeak=V/R. Irms=Ipeak*root2. for Prms use Vrms and Irms.

To know your psu voltage under load this little tool is helpful: http://www.duncanamps.com/psud2/psud2_setup.exe

 

[Mad_K]

How do you calculate the efficiency of the heatsink needed? Then you would have to calculate the heat dissipated by the IC, how to do that?

Lots of questions in this neewb head.

use this graph (close enough -lm3875 datasheet)