ua739 Op Amp Replacement - diyAudio
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Old 19th September 2006, 10:08 PM   #1
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Default ua739 Op Amp Replacement

I would like to replace this dual op amp with new op amps but it has some features I am not familiar with and I having difficulty find sutitute(s). I'm not looking for pin to pin replacement.

Look at the LAG PINS, it seems to have more in's and out's than a typical op amp. I'm used to Vin+ Vin- and Vout+ Vout-

Cheers,

Shawn.
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Old 19th September 2006, 10:09 PM   #2
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Default The circuit

It is in the DC300A and here is a look see:
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Old 19th September 2006, 10:12 PM   #3
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Default Op on the right

The right hand portion of the schematic shows the use of these other leads. It's hurting my brain and makes me want to drink vodka.

Shawn.
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Old 20th September 2006, 02:37 AM   #4
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You will not find a drop-in replacement, if that's what you're hoping for.

Perhaps someone can explain what's up with Q119/Q219...
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Old 20th September 2006, 02:59 AM   #5
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Can try to replace it with modern bipolar input opamp,but need to deal with different pinouts.
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Old 20th September 2006, 03:11 AM   #6
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Default uA739

from the data sheet of the uA739:

These three stage amplifiers use Class A PNP transistor output stages with uncommited collectors

Uncommitted colectors! I guess the uA739 has extra connection possibilities that are tied up and committed inside of a regular op amp. Can we eliminate some of this external circuitry knowing it already exists inside the modern op amp version? Or is it critical to this particular circuit?

Pin for pin replacement is way out of the question.


Shawn.
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Old 20th September 2006, 06:53 AM   #7
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Default Re: uA739

Quote:
Originally posted by TomWaits
from the data sheet of the uA739:

These three stage amplifiers use Class A PNP transistor output stages with uncommited collectors

Uncommitted colectors! I guess the uA739 has extra connection possibilities that are tied up and committed inside of a regular op amp. Can we eliminate some of this external circuitry knowing it already exists inside the modern op amp version? Or is it critical to this particular circuit?

Pin for pin replacement is way out of the question.


Shawn.
The 'uncommitted collectors' but means it is really a single ended amplifier.

Jan Didden
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Old 20th September 2006, 07:26 AM   #8
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Has the uA739 gone bad, or are you looking for an upgrade?? They can still be found as old new stock, usually on dusty backroom shelves. Other comparable numbers are MC1303 and ECG725 (not to be confused with the uA725). An NE5532 would probably work as well in the application with some circuit tweaking (basically removing the components unique to using the 739, e.g. Q119, C102, D111, etc). There isn't really enough of the surrounding circuit in your pic to know for sure in terms of oscillation issues though. The 5532 also draws a bit more current, though I doubt that'd be an issue. If it were me, I'd just replace the 739 if it's gone bad. I don't think I'd bother trying an upgrade. I sort of liked the sound of the 739 in its day anyways, though yes, it is obsolete by current standards.
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Old 20th September 2006, 11:33 AM   #9
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He wants to hot-rod it, and I can't blame him for wanting to find a way to junk that 739.
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Old 20th September 2006, 11:47 AM   #10
AndrewT is online now AndrewT  Scotland
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Hi Tomwaits,
have you read the WJung series on cascading opamps to get the benefits of superlative input/voltage amp parameters combined with the excellent current ability of a buffer on the output.

eg. a FET opamp driving 75ohm terminated cables using a buffer.

Extrapolate that practical advice to an ICopamp input into a power amplifier used as the buffer and you have the makings of excellence while sticking sort of loosely to the Crown philosophy.

At bit at odds with my vote to rebuild the DC300, but close(ish).

I am thinking about (I do too much thinking and not enough making) modifying my Sugden P128s to exactly this. They have separated stages, 5534 input followed by the power amp. I would like to hear the benefit of integrating the amplifer with the input opamp as Jung.
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