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Old 6th October 2013, 09:19 PM   #1
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Default AD797 overheating (ANZ flavor)

I am testing an AD797ANZ in a filter circuit and I noticed that on quiescent state the amp is drawing around 60mA from the PSU (+/- 15V). This makes it heat because it has to dissipate 2W.

I built a simple circuit of inverting amp (2 10-K resistors, 0V input, 0V output) and it still does the same.

I have a bunch of 10 which I bought off eBay. They all do that.

Is this normal?
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Old 6th October 2013, 09:42 PM   #2
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This is not normal. I would tell your supplier that they are faulty and ask for a refund. Always buy from a trusted supplier like Mouser, Farnell, RS Components and the like.
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Old 6th October 2013, 09:46 PM   #3
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That chip is very sensitive to layout and PS bypassing issues which can make it prone to HF oscillation, and it's not really the best choice for unity gain operation. I personally don't like to buy parts from unknown/untrusted sources, lots of fake components out there. Having said all that, what kind of filter were you trying to build and what do you want it to do? A schematic would be helpful.

Mike
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Old 6th October 2013, 09:50 PM   #4
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Open door: how is the power supply decoupling arrangement ? As posted by other members AD797 is very sensitive and I have seen them oscillating more than once.
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Old 6th October 2013, 10:27 PM   #5
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The power supply is a lab power supply (Agilent). I think the parts are probably fake. This happened to me a couple of times. The sellers had a very positive feedback.

I will try decoupling the power supply and see how it goes.

For the filter, it was in fact a tone control circuit. I am new at DIY audio and still at the learning stage.

Thanks all for your answers, really appreciated.
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Old 7th October 2013, 05:42 AM   #6
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Decoupling the supply pins straight at the AD797 would be wiser.
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Old 8th October 2013, 12:57 PM   #7
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Quote:
Originally Posted by jean-paul View Post
Decoupling the supply pins straight at the AD797 would be wiser.
Absolutely necessary, actually.

It seems that the OP didn't bother to even look at the AD797 datasheet other than to drool over the low noise and distortion figures. It spells out some very specific recommendations for stability, among them are some strict decoupling requirements.
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Old 8th October 2013, 02:41 PM   #8
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Please post a schematic. This is groping around in the dark. There are many ways this can happen. For instance, is the 60mA from both rauils or only from one rail? How hot does it reaaly get, just hot to the touch or too hot to keep your finger on it?

Jan
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Old 8th October 2013, 02:43 PM   #9
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Quote:
Originally Posted by macboy View Post
Absolutely necessary, actually.

It seems that the OP didn't bother to even look at the AD797 datasheet other than to drool over the low noise and distortion figures. It spells out some very specific recommendations for stability, among them are some strict decoupling requirements.
This is too harsh - we don't even know what the cause is! You judge without having a clue.

Jan
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Old 9th October 2013, 01:20 AM   #10
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What are you suggestions for capacitors values for effective decoupling?

I tried 10uF with 100nf straight at the pins, same result. Please bear with me as I am a noob.
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