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Old 14th April 2009, 07:31 PM   #1
Artie is offline Artie  United States
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Default Headphone amp circuit question.

Hi all. I hope you can help me to better understand a couple of "headphone amp" options. I've been wanting to build a nice quality headphone amp, and have been looking over the circuits at Headwize for quite some time. But I'm also intrigued by National's LME series of chips. Here's what I'm trying to figure out:

Look at this circuit: (Reduced version of circuit taken from the LME49600 data sheet)

LME49600

This circuit seems so much more complex than many of the Headwize offerings, such as the Cmoy/Grado, and others. I would even think that a simple LME49720, driving something like an LH0002 buffer, (or BUF634), would still provide good fidelity.

So, my question is: what kinds of benefits are there to building the more complex 49600 circuit?
Btw, my current headphones are Beyerdynamic DT-770 Pro's. (250 ohm, 100mW max.) My primary source will be the Wolfson DAC output of a Chaintech AV-710.

Thanks all.
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Old 15th April 2009, 06:36 AM   #2
Dxvideo is offline Dxvideo  Turkey
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B signed opamps are for dc servo. Thus provides a DC coupled dc offset free amplifier (in limited margins).. You can omiit this function by eliminating B opamps (you may use just one dual opamp for all)..
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Old 15th April 2009, 06:54 AM   #3
dedick is offline dedick  United States
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It looks more complex at a glance because it shows both channels, whereas most amp schematics only show one.

The only real added complexity on this circuit compared to most other buffered headphone amps is the additional opamp in the feedback loop. This is a servo to eliminate DC offset voltage on the output. Most headphone amps wouldn't need this. Maybe this combination isn't very stable and needs a servo where other chips wouldn't? I'm just guessing here. It might just be design overkill.
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Old 15th April 2009, 09:08 AM   #4
Artie is offline Artie  United States
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Thanks Dx and De. I guess that makes sense. Its just funny that a dedicated "headphone amp" chip needs all that support circuitry. I may go ahead and build it just to see how it sounds.
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Old 15th April 2009, 01:57 PM   #5
Dxvideo is offline Dxvideo  Turkey
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This opamps are relatively new series and I dont have any idea about their sound quality..
However, if their sound is comparable with old LM4562 series then its worth to try I guess.
But if you need a "tested" alternative then TPA6120 will be a good canditate for a hi-quality headamp..
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Old 15th April 2009, 07:32 PM   #6
Artie is offline Artie  United States
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Thanks Ozgur. I'll look into that one also.
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