OPA549 bridged into 4-ohm

[soundNERD]

Can I do that? I want to drive a 4-ohm sub speaker with a bridged OPA549. Can they handle 2-ohm loads?

if so, about how much power can be expected from it?

if not, can i use an opa541 bridged into 4-ohm? same question, how much power?

Thanks, Mike

[carlmart]

Originally posted by soundNERD
Can I do that? I want to drive a 4-ohm sub speaker with a bridged OPA549. Can they handle 2-ohm loads?

if so, about how much power can be expected from it?

if not, can i use an opa541 bridged into 4-ohm? same question, how much power?

Power will depend on what voltage you are using. 4ohm speakers and bridge do not speak to each other well on chips, except if you parallel too. Max voltage will also be limited to a top +/-35v, but you could get to at least 200W in 4 ohms.

Transformer current should be high and heatsink large too.


Carlos

[soundNERD]

I'm using a torrid originally used to power an entiere surround speaker system, so current is not an issue. The transformer puts out dual 44VCT secondaries, and I do not know how much that is after rectifiers.

so are you saying that this chip will work bridged into 4-ohm to get 200W, or that I would get 200W into 4-ohm by paralleling it?

[carlmart]

Originally posted by soundNERD
I'm using a torrid originally used to power an entiere surround speaker system, so current is not an issue. The transformer puts out dual 44VCT secondaries, and I do not know how much that is after rectifiers.

Don't trust surround speaker systems too much, particularly if they are low priced.

22v + 22v should output around 29v after rectification. Should be enough.

Originally posted by soundNERD
so are you saying that this chip will work bridged into 4-ohm to get 200W, or that I would get 200W into 4-ohm by paralleling it?

What increases the power is the bridge, the higher load is taken care by the parallel.

Exact power is not easy to compute on the 549, as many factors are involved. The 200W I mentioned really apply on LM3875/3886 chips.

TI does not publish a power curve, so we can only conjecture what you can get. Let's be conservative and say 40 watts at 8 ohms and 60watts for 4 ohm. So I'd say you can expect at least 120W for an 8ohm bridge and perhaps 180W for ohm, paralleling at least two pairs on each bridge.


Carlos

[carlosfm]

Be careful, the OPA549 only handles 2x30v PSU rails maximum...

[soundNERD]

its not a cheap surround system. its from my broken logitech z-680s.

I was wondering why the thing cranked out so much heat and why it only worked with a 16ohm speaker (two 8ohm in series). if i tried an 8 or 4 ohm speaker, it just made a popping sound on any volume not much above minimum.

it ends up that i was getting +/-33V supplies, so I am suprised the smoke didn't escape from the chips.

I put it on a +/-24VDC supply, and I was able to run a 4-ohm speaker perfectly fine, and I even tried connecting an 8ohm and 4-ohm in series and it was still stable.

This amp sounds much better and handles lower impedence load than any gainclone I have ever built. My (cheap) onkyo amp goes into protect mode with a 2ohm load, yet this thing doesn't even struggle with it.

this is by far the best amp I have ever built.

but now, i face a problem. I have no transformer powerful enough for this amp, and 2 amps for the tweeters (two 3886 amps) beside the one from the z680s. The 3886 amps are fine with it, but not this one. How can I reduce the power being supplied to these chips without losing current. I'm thinking of diodes??

Thanks,
Mike

[Hybrid fourdoor]

I'm thinking a cheap 24V trafo from PE, would be far easier and efficient than all those diodes

[soundNERD]

theres no point buying something when I already have it,

How ineffecient would diodes be?

[carlmart]

Originally posted by soundNERD
it ends up that i was getting +/-33V supplies, so I am suprised the smoke didn't escape from the chips.

It proves the chip is quite well built and has some tolerance. Don't try that again. What you can do is regulate those +/-33v onto +/-29v.

Originally posted by soundNERD
I put it on a +/-24VDC supply, and I was able to run a 4-ohm speaker perfectly fine, and I even tried connecting an 8ohm and 4-ohm in series and it was still stable.

The question is not stability, but the load being heavy. It gets heavier as the load is smaller, so 12 ohms wouldn't be a problem. Now if you parallel the speakers that would increase the load.

The stability is always related to capacitance drive, which might be a problem with some cables that can have high capacitance.

Originally posted by soundNERD
but now, i face a problem. I have no transformer powerful enough for this amp, and 2 amps for the tweeters (two 3886 amps) beside the one from the z680s. The 3886 amps are fine with it, but not this one. How can I reduce the power being supplied to these chips without losing current. I'm thinking of diodes??

You shouldn't reduce power with anything but a regulator. Whatever else you add will take precious VAC away, leaving nothing but heat. Regulate them and kill two birds with one stone.

But if I were you I would try the 3886 on the sub and the 549 on the tweeters.



Carlos

[carlosfm]

No...
The OPA549 is good, but the 3886 has better midband and treble, it's really another league.
It would be better for the tweeters.