OPA549 disappointing

[la9]

Just finished one channel of my new OPA549 and have to say I don't like it at all. I'll say that it sounds good at low volumes but once you start getting loud with it, it distorts too badly for my taste.

The LM1875 is far better choice in my opinion. Still my chip of choice.

 

[peranders]

Are you sure you don't drive the IC into clipping or you are having oscillations?

 

[Mad_K]

how much gain do you use?

 

[pinkmouse]

Is your heatsink big enough?

Are you clipping your speakers?

Is your PSU powerful enough?


I think you get the general idea, your findings are unlike other people that tried this chip. If you give us some idea of your setup, we may be able to solve your problem.

 

[la9]

Here is why the distortion. Had gain set at 18. Didn't think it was loud enough so changed feedback resistor with 1 meg resistor giving me a gain of 100. I still had adjustment through volume control. The distortion was from setting the gain too high and cranking it up. I thought I'd see what I could get this chip to do by setting the gain higher.

Set the gain back to 18 and all is well. Problem is I was expecting alot more volume from this chip.

Power supply is +- 25 at 4 amps. Should be OK.

Heatsink seems to be carrying itself, it isn't shutting down from being too hot.

Unless anyone has ideas on anything I can do to make it louder I think the next project will be bridging two together.

Looks like I LOVE IT LOUD.

Thanks everyone

 

[Rookie]

OPA549 has a gain bandwidth product of 900kHz. With a gain of 100 it makes a bandwith of 9kHz with great distortions at higher frequencies, which makes it completely useless for audio. I'm not surprized it didn't sound well. This chip must be used with lower gain.

 

[peranders]

I think you maybe have underestimated how many watts you really need. Maybe we are talking about 100 watts or more?

 

[Mad_K]

OPA549 should not be used with gain higher than 10x in audio applications

 

[carlosfm]

Somethig different

Here's a good opportunity to make something different.
OPA549 as a buffer, with a gain stage before it.
OPA637 biased into class-A?

 

[Franz G]

Maybe there is in fact better choice than the OPA549:

this chip works at 20kHz with an open loop gain of just 35dB, what is the (low) level of an uA741

Franz

 

[theChris]

you'd have to power the opa549 and 637 off of equal rails. the opa637 is limited to +-18V, while the opa549 can go much higher.

 

[Mad_K]

OPA604 @6-12dB gain and OPA549 @20dB is a shure shot! you could even power both of +/-24V... (I would use regs to +/-15V on the OPA604 though)

 

[JojoD818]

I have both LM3875 and OPA549 in non-inverting configuration playing right now. Frankly, I like both of them very much.

Maybe the 549 is comparable to a 741 like Franz G said but still, I like how it plays music.

Just me.

 

[carlosfm]

you'd have to power the opa549 and 637 off of equal rails. the opa637 is limited to +-18V, while the opa549 can go much higher.

You're right.
OPA552 seams perfect for this job.
Check it out.

 

[JojoD818]

Re: Somethig different

Here's a good opportunity to make something different.
OPA549 as a buffer, with a gain stage before it.
OPA637 biased into class-A?

Carlos,

This is very interesting, an opa637 with a gain of 20-22? Then a 549 in unity gain... is it possible?

JojoD

 

[carlosfm]

Yes, but you can't go higher than +/-18v PSU voltage.
Other op-amps can handle more.

 

[JojoD818]

Yes, but you can't go higher than +/-18v PSU voltage.
Other op-amps can handle more.

How about +/-18v for the 637 and +/-25v for the 549?

I think I'll try this.

 

[carlosfm]

Jojo, why don't you read this thread from the beginning?
You are making questions that have been answered here.
This thread is only 2 pages, read it.

 

[JojoD818]

Jojo, why don't you read this thread from the beginning?
You are making questions that have been answered here.
This thread is only 2 pages, read it.

Carlos,

I was reading it since the beginning of the thread. I was just confirming it though. So sorry if I disturbed you.

Thank you,
JojoD

 

[ybserge]

OPA549 should not be used with gain higher than 10x in audio applications

Not absolutely. It works fine at 19 when combined with a tone circuit preamp. I did what I found from here http://yooree.narod.ru/tale_3.chm - nice staff. Unfortunately eveything is in Russian.