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Old 6th August 2003, 10:00 PM   #1
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Default Need help with opa549 e/s pin

I would like to make a few gainclones based on the BB opa549 chip and am wondering what to do with the E/S pin, can I just drop a resistor to ground? If so what value would you use?

I also want to run them into a 4 ohm load, what supply voltage would be the best to use for that load and how many watts could I reasonably expect? Would the OPA541 or LM3886 be a better choice?

Sorry for all the questions, Punch
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Old 7th August 2003, 08:20 AM   #2
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you do no need to connect anything to this pin. it can be used to switch the output, but if left unconnected, the amp will run fine. the output status can also be indicated using an LED connected from this pin to ground.
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Old 7th August 2003, 08:29 AM   #3
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I just clip them off, it saves confusion during wiring.
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Old 7th August 2003, 02:25 PM   #4
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Quote:
Originally posted by pinkmouse
I just clip them off, it saves confusion during wiring.
Yes, CUT IT OFF.
I would also like to know the power vs supply voltage of the OPAs.
The datasheets don't have these graphs.
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Old 7th August 2003, 08:03 PM   #5
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youll have to work out the power rating. see here: http://diyaudio.com/forums/showthrea...threadid=14768
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Old 8th August 2003, 08:12 AM   #6
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Thankx Matttcattt,
That helps.
A graph would be better but you can't have it all...
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Old 8th August 2003, 01:57 PM   #7
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I just wanted to thank everyone for the help so far.

"If the supplies are +/-20v, your peak output swing will be 16.4v whereas the RMS will be 16.4 * 0.707 = 12.6v. This will result in an RMS current of 1.45A into 8R, giving 16.82W RMS output power."

OK someone suggested to me I use +/- 24 V rails, and from the calculations above i get ~55 Watts of power.

What I am wondering is if the 549 is stable at it's max of +/- 30 V into a 4 ohm load, or would something like the lm3886 at 68 watts be a better choice? Since the 541 can handle +/- 40 V can it put out more power into the 4 ohm load I will be using, or would it not be stable enough? I'm still learning how to read the white papers on these chip amps.

Thanks
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Old 8th August 2003, 10:52 PM   #8
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The 549 is excellent, but I had problems when I was running it at 30V rails, the autoprotect kept cutting in. And this was with nice even 8ohm speakers.

Mine is currently running beautifully on 24V rails, with the traffo modded by unwinding some of the output turns.

I didn't used to like the LM3886, but I may be doing some further experimenting with them at some point, as I have found an application in which they sound very good indeed.
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