What is this chip?
Jul 16, 2008 at 9:19 PM Thread Starter Post #1 of 10

trodas

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X-Fi_mic_input_chip.jpg


This is a chip on my X-Fi that is probably a input opamp, because it definitively pass the audio signal from the mic... but searching for M33078 returned only results like:
http://www.alldatasheet.com/datashee.../ADM3307E.html
ADM3307E - 15 kV ESD Protected, 2.7 V to 3.6 V Serial Port Transceivers with Green Idle

...witch is certainly not the chip we see above. Any help/ideas what it is and mainly a Hi-Fi replacement suggestion?
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Jul 16, 2008 at 9:30 PM Post #2 of 10

looser101

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Jul 16, 2008 at 11:25 PM Post #4 of 10

trodas

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Jul 25, 2008 at 9:09 AM Post #7 of 10

trodas

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Damn!
The suggested replacement for the MC33078 opamp, the AD8599 one seems to be good choice, but...!

This time the opamp is powered from +5V only (the leg 8), leg 4 is NOT connected to the -5V as all other opamps there on the X-Fi Fatal1ty - but to ground. Hence this one is getting only 5V. AD8599 require by specs at least 9V. I'm affraid that it will not work good there... time to find another opamp, +5V capable one
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Jul 25, 2008 at 11:13 AM Post #8 of 10

error401

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Well, MC33078 requires +/-5V (10V rail to rail) according to the datasheet. Are you sure? That'd violate the specs on the device, and wouldn't make much sense either...

You could try LME49720 (LM4562), it will run on +/-2.5V so it should work - but I really suspect that you're mistaken.
 
Jul 26, 2008 at 9:17 PM Post #9 of 10

trodas

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Sorry, I'm not.
All four X-Fi opamps are powered from +/-5V. All their pins 8 and 4 and connected to the output of 7805 and 7905 regulators. On the end of the line, there is additional cap on the +5V line.
Probably/likely for the MC33078.
Pin 8 of the MC33078 is connected to the +5V line, as other opamps are. Pin 4 is ground, tough...

When pin 4 is ground, it can only be, that the opamp is giving +5V only.

Sorry, this is very simple measuring and I did it twice to be sure. I cannot be wrong on this one.

I did not check that "on the fly", but if the pin 4 on ground get somewhat flipped when MIC is enabled by some transistor to the -5V, then it has to be connected to the transistor and not to the ground with zero resistance... Hence even on the fly things can't differ from my findings that the MC33078 is powered by +5V only. Weird, out of specs... but Creative is simply sometimes being too creative.

Regardless, LM4562 sounds as interesting alternative, but it is a known picky opamp that likes to pick RFI a lot... so I'm somewhat not happy from the idea...
I rather push on the AD8599 and try it there. Why? Because in THIS thread: http://www.head-fi.org/forums/f6/sta...9/#post3536731

Is the AD8599 (among ohers) run from 3.7V lithium batteries and it works. His specs might be kinda different from what the datasheet says, tough the LM4562 sound too harsh/sharp to me... maybe is the AD8599 still better choice even at +5V only?
 

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