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Old 26th September 2012, 12:26 AM   #1
earplay is offline earplay  United States
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Default Uh oh! A quick op amp question

Looking before I leap. As a newb, I'm wondering if I can switch the op amps on my Music Hall 25.2 CD player. The original op amps are four Burr-Brown OPA-2604's. I'm thinking it might be good to replace them with four National Semiconductor LM4562NA/NOPB DUAL HI PERF,HI FI (from Mouser).

Is this okay to do? Just pull the old ones and put in the new.

I think this is the case. I believe this op amp has been used to replace the stock op amps in the 25.2 CD player as I describe here. Not knowing the specs of the op amps involved, I'm going on what I've read regarding modding this cd player.

Last edited by earplay; 26th September 2012 at 12:51 AM. Reason: clarification
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Old 26th September 2012, 12:55 AM   #2
DUG is offline DUG  Canada
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Check the supply as the opa is +-25V and the LM is +-18

Other than that I am liking the LM's even though my ears would not be able to tell the difference. (but my mind would)
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Old 26th September 2012, 01:03 AM   #3
earplay is offline earplay  United States
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Thanks DUG!

See, I was afraid this would happen. Right off the bat I'm in over my head. I don't know how to check the supply. I don't have the tools to check the supply. I don't know where to find information about the supply. I'll google around a bit now, tho.

From what you say, the 25.2's supply may be too great or too small for the LM, is that right?
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Last edited by earplay; 26th September 2012 at 01:04 AM. Reason: clarity
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Old 26th September 2012, 02:07 AM   #4
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Might be too great as the OPA can survive 48V total. You need to check with a multimeter between pins 8 and 4 of the opamps. 34V or below and you'll be good to go.
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Old 26th September 2012, 02:58 AM   #5
earplay is offline earplay  United States
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Thanks abraxalito. I had a multimeter, but I a friend has it and it's far, far away. I'll have to get another and measure across those pins.
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Old 26th September 2012, 10:18 AM   #6
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Hi earplay
If CD have a PCM1738 which value of DAC current output is 2.5 mA +/- ???
And why you don’t play with resistor I/V conversion? And kill the op amp ( avoid bunch of “complication” )???
Simplicity is the best way.
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Old 26th September 2012, 11:24 AM   #7
DF96 is offline DF96  England
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The OP has admitted that checking the supply could be over his head. You want him to replace the entire circuit with passive I/V?
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Old 26th September 2012, 02:00 PM   #8
qusp is offline qusp  Australia
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but simplicity is the best way? surely this will win through?
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Old 26th September 2012, 02:59 PM   #9
earplay is offline earplay  United States
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Off topic, but I am astounded when I see the flags of the various countries represented here. I want to thank every one of you.

So far, I've installed Vishay MKP1837's to bypass the output coupling(?) caps, removed the RCA wire connectors soldered to the board and the stock wire. I soldered directly to the board Ohno single crystal copper wire to connect to the RCA jacks. Just these things made a very noticeable improvement.

Something I can pass on that might be helpful is the use of Vishay MKP1837 as bypass caps. It's a tip I picked up at The Lab on the AudioCircle site. I can point you directly to the thread if anyone is interested.

Now I am planning to pick up another multimeter. Any suggestions for a good multimeter when low price is important? I have a Radio Shack nearby.
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Old 26th September 2012, 03:55 PM   #10
DF96 is offline DF96  England
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Quote:
Originally Posted by qusp
but simplicity is the best way? surely this will win through?
One man's simplicity is another man's incomprehensible complexity.

Maxwell's equations look a lot simpler (to a high energy physicist) when written in relativistic 4-space notation, as the artificial distinction between electricity and magnetism disappears, but I doubt if many EEs would see them as simpler. Fourier theory is a simple application of inner product spaces.

Similarly, an experience DIYer might see passive I/V as simpler than an opamp virtual ground circuit for terminating a DAC, but someone who just wants to swap an opamp might find the reworking rather daunting. Also, many passive I/V circuits push the DAC well outside its written spec in terms of output voltage so are likely to introduce distortion - it might even be this distortion which some people like! Don't make things too simple, as 'too simple' does not work.
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