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Old 13th July 2014, 12:31 PM   #1
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Default Best sounding chips for preamp & headphone amp

I know this is a potentially hot question, but if we can cool the issue down perhaps we can get some stories on what worked best for everyone.

I'm working on a project where the supply is 12v single, so I do have to use input and output caps, usually large ones.

But the chip used will probably leave its mark on the audio quality.

The first contenders I have are the MC33178 and the NJM4556.

The headphone chip has to have good current capability, be able to move 50-75ohm caskets to good levels, probably even 600ohm ones too, which is not an easy task.

Using boost drivers for the headphone amp is not out of the question.

Your experience and suggestions please?
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Old 13th July 2014, 12:51 PM   #2
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AD815 with outputs loaded with CCSs according to how much classA operation is desired. Even with CCS loads it benefits a lot from a passive shunt regulator (lots of paralleled electrolytic caps).
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Old 13th July 2014, 12:55 PM   #3
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Sorry, I forgot to explain that this a portable project, and it will be all SMD.

Class A operation is probably out of the question. Do not forget it's also 12v single supply.

None of those variables can be altered.
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Old 13th July 2014, 01:00 PM   #4
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Originally Posted by carlmart View Post
The first contenders I have are the MC33178 and the NJM4556.

The headphone chip has to have good current capability, be able to move 50-75 ohm caskets to good levels, ....
I'd wonder if these two are capable driving such a load.
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Old 13th July 2014, 01:06 PM   #5
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I use AD815s (but without the CCS loads to save on juice) in my portable DAC, and yes its SMD the through-hole variant is obsolete.. However my supply rails are about 6V and I use a trafo to interface to the headphones as mine aren't wired for balanced.
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Old 13th July 2014, 03:06 PM   #6
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Originally Posted by ticktock View Post
I'd wonder if these two are capable driving such a load.
They probably are, even more if I add the boost transistors. But even without them I think they would.
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Old 13th July 2014, 05:47 PM   #7
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Quote:
Originally Posted by carlmart View Post
The first contenders I have are the MC33178 and the NJM4556.

The headphone chip has to have good current capability, be able to move 50-75ohm caskets to good levels, probably even 600ohm ones too, which is not an easy task.
NJM2113 is designed specifically to drive 32-ohm headphones, and will work from a single 2 to 16V supply.
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Old 13th July 2014, 09:19 PM   #8
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Thanks for the tip.

It's interesting how some NJM chips are not well known, and so with very few people using them to report back.

There's a limiter chip by them, the NJM2762, which is a stereo limiter, that I could not find a single application for it on the web. Support is nonexistent, so a chip that is probably easy to setup has no one to answer simple questions on how to assemble things in order to work properly.
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Old 14th July 2014, 01:20 AM   #9
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One possible problem about that chip is frequency response.

They claim it's for telephone application, and they say it's gain adjustable in a 5KHz bandwidth. That doesn't sound very promising, does it?
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Old 14th July 2014, 07:49 AM   #10
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It seems to have sufficient GBW - the info in the datasheet seems to assume a 40 dB gain (probably the norm in telephony applications). For a typical headphone amp with 6..10 dB gain, both the distortion numbers and the BW should improve to cover the full audio band.

I'm trying to see how to nest it within an outer feedback loop of another opamp, a la Walt Jung. If it's workable, then the NJM2113 can just be used for current capability, while the outer opamp will define the sonics.
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