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Old 30th August 2004, 04:14 AM   #1
la9 is offline la9  Czech Republic
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Thumbs down OPA549 disappointing

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.
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Old 30th August 2004, 05:34 AM   #2
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Are you sure you don't drive the IC into clipping or you are having oscillations?
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Old 30th August 2004, 05:56 AM   #3
Mad_K is offline Mad_K  Norway
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how much gain do you use?
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Old 30th August 2004, 08:45 AM   #4
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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.
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Old 30th August 2004, 10:00 AM   #5
la9 is offline la9  Czech Republic
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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
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Old 30th August 2004, 10:12 AM   #6
Rookie is offline Rookie  Serbia
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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.
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Old 30th August 2004, 10:58 AM   #7
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I think you maybe have underestimated how many watts you really need. Maybe we are talking about 100 watts or more?
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Old 30th August 2004, 01:05 PM   #8
Mad_K is offline Mad_K  Norway
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OPA549 should not be used with gain higher than 10x in audio applications
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Old 30th August 2004, 03:11 PM   #9
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Cool 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?
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Old 30th August 2004, 04:11 PM   #10
Franz G is offline Franz G  Switzerland
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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

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