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Old 19th September 2011, 08:29 PM   #11
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Some guy offered me some NTE778S opamps. Can anyone tell me if these ops are a direct replacement for the NJM4556?
I can't find the 4556 in the NTE cross reference bible.
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Old 19th September 2011, 08:39 PM   #12
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Does not look much like a 4556 to me based on the datasheet.

I'm still confused about your project - are you proposing to drive several headphones from a single chip or are you open to using several chips?

Also confused about why you are fretting over jellybeans. The njm4556dd is less than a dollar pretty much anywhere.

What are your project goals and constraints?

(also, wrt the 2086 confusion - I must have been looking at the dissipation column, sorry.)
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Old 19th September 2011, 09:30 PM   #13
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You must have gotten something wrong. I never said I want to use one chip to drive several headphones. I am and always have been open to using several chips. It is - AFAIK - the only "right" way.
By the way, I made a multiple headphone amp (1x in - 6x outputs) with 12x LM386's and swapped them for 6x NE5532's: these ones may have a little less volume but they sure produce much less distortion and sound much cleaner.

Sooo, are you saying that the NTE788S is not the same as the 4556? On the datasheet it says that "it is also suitable as a headphone amplifier because of its high load current"
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Old 19th September 2011, 09:45 PM   #14
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The NTE788S has more than twice the slew rate, 2 volts less maximum operating voltage, and drives 50mA vs. the 4556's 70mA. They are not remotely the same chip. There are a lot of chips it could be, and i'm not really interested in finding out.

It would certainly work. If you're getting them for free, go for it.

Beefer options include the opa551, or a single opamp driving a raft of buf634, but those are expensive options.

There are numerous TO220-5 power opamps out there, but headphones don't need much power.

You can also drive a power BJT or darlington within the feedback loop of an opamp. Like so:

Click the image to open in full size.

Above is the "Tori" headphone amplifier, as designed by he who calls himself PRR on various fora. A quick google search will reveal discussion of this version, and the power mosfet version. You could reduce the power requirements by reducing the bias load on the transistors.

It shows a TIP41 but you can use any npn power BJT used in audio - bd139, mje243, etc. Also darlington parts like TIP120. This amp will drive small speakers if it has to. If you plan to use low-Z headphones you may want a 10ohm or so resistor padding the output.

Most people who built this amp used an lm317 configured as a current regulator for the current sink. at 200ma it will need a heatsink, and the output resistor should be maybe 1W or bigger. 200ma out of an lm317t = 6.2ohms, fwiw. 100ma would be 12.4, etc.

Last edited by ericj; 19th September 2011 at 10:00 PM.
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Old 19th September 2011, 11:55 PM   #15
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ah, sorry, made another mistake, slew rate is the same between nte778s and njm4556. But they are still not the same chip.

there is a 1mhz difference in gain/bandwidth product, the nte part is rated for low voltage use and the njm is not, etc.

Similar. Not the same.
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Old 20th September 2011, 12:56 AM   #16
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Copy the circuit in RocketScientist's O2 and make multiple sections, one for each output. I don't think you'd be infringing his intellectual property rights, it's hardly a revolutionary design, besides, as he says much is in the implementation (layout). Drive them all from a single unity gain buffer. You could include a master volume.

Make a good job of it, e.g keep the power rail tracks close together and follow a good star grounding scheme, use plenty of bulk capacitance suitably distributed with 0u1 ceramic caps at each chip power pin, and you'll end up with a result that won't leave much room for complaint, and it'll be about as cheap as it can be done.
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Old 20th September 2011, 03:55 AM   #17
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I should add that i have used the 4556 in a headphone amp and i find it "punchy" and totally adequate but "unrefined". Grado uses it in their outrageously expensive RA-1 headphone amplifier, but i don't care for their headphones.

I like the 4580 sound signature better but it doesn't have the current ability, needs buffered. for neutral on a budget you want njm2068 and it will drive most headphones 60ohms on up.

really i prefer chips like the opa2107 and lm4562 aka lme49720 (or lme49710 for single-channel) but they don't have much in the way of power output, though the 4562 is good for oldschool 600ohm studio monitor cans.
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Old 12th November 2012, 05:49 AM   #18
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Jrc4558/2068 or NE5532 is useful for line driver applications or unity to some moderate gain (say max 10X gain like in h/p amp gain stage)application. Jrc4556 is unity gain stable & can be used to drive h/p directly(lowest upto 16 ohms). You can use Jrc4558/2068 for gain stage - "x" no. of 10K log pot for vol. followed by "x" no. 1uf polyester/polypropelene series cap. to block out any DC & "x" no. Jrc4556 in unity gain mode to drive "x" no. h/p.

http://nwavguy.blogspot.in/2011/08/o...ths-facts.html

Last edited by availlyrics; 12th November 2012 at 06:06 AM.
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