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Old 19th August 2011, 05:26 PM   #1
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Default NJM4556, NJM4558

Hi.
I know that the NJM4556AD works OK in a multiple headphone amp.
How about the NJM4558? Its data sheet says nothing about "high current", but it also says nothing about "output current".
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Old 19th August 2011, 06:33 PM   #2
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My goal is to build such an headphone distribution amp. Are there any other options, i.e a multiple pin TO220-ish size.
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Old 19th August 2011, 08:00 PM   #3
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You need separate output buffers for each output. As long as the current is enough to run any set of phones you are fine.

Ask your self, what happens when someone plugs in two sets of 32-Ohm cans? They will each need separate volume controls as well. Because, what happens when someone plugs in a set of 600-Ohm phones and then a set of 60-Ohm?

Gain stage needs to be rail to rail. Trust me. You don't want anything normal to be able to be able to clip the gain stage. You can attenuate before the output buffer with a shunt. Which is exactly what a pot is. You will probably have to use fixed resistors as well for additional attenuation control. Or you can use a 3 position switch where the values are closely matched. Then there are no problems with someone not having enough pot travel and someone having too little.
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Old 21st August 2011, 12:16 AM   #4
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So you are saying that any desing based on the NJM4558 or the NE5532 would work just fine?
I also need to put a connection for a talk-back mic in the circuit.
I want to use the whole device after a small M-Audio digital console witch has no TB-mic in and convert it from one headphone out into six outputs.
I was thinking of taking the balanced receiver designed by ESP and go right into a NE5532 based circuit before each buffer opamp with a momentary switch that when activated converts the stereo out into mono and when released puts it back to stereo.
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Old 21st August 2011, 05:05 AM   #5
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Quote:
Originally Posted by PhantomBox View Post
Hi.
I know that the NJM4556AD works OK in a multiple headphone amp.
How about the NJM4558? Its data sheet says nothing about "high current", but it also says nothing about "output current".
Sure it does but it says it with a graph. It's called maximum output Voltage vs load resistance. The 4558 won't get any prizes for output current. With dual 15 Volt supplies it will do 28V into 10K, 25V into 1K, 22V into 500 but it's falling off a cliff now. 16V into 300 Ohms and the graph stops at 12V into 220 Ohms. Not a good choice for driving low loads. It's also slower than mud at 1 V/uS slew rate. It _would_ make a fine 8 pin thumbtack though.

The graph is on page 3 of the JRC NJM4558 data sheet.

G

Last edited by stratus46; 21st August 2011 at 05:07 AM.
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Old 23rd August 2011, 07:58 PM   #6
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I will opt for an LM386 design. I think it has enough output.
No I'm trying to figure out a way to add the TB-mic to the project.
Any ideas?
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Old 23rd August 2011, 08:45 PM   #7
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Quote:
Originally Posted by PhantomBox View Post
I will opt for an LM386 design. I think it has enough output.
No I'm trying to figure out a way to add the TB-mic to the project.
Any ideas?
Not the lowest distortion but certainly easy to get, inexpensive and obviously capable of the headphone load. You can probably use your 4558 as a mic preamp. For intercom use (that's what it is?) the limited performance of the 4558 should be fine. With 2 stages, 25-35dB of gain shouldn't be a problem for a dynamic mic but it will depend on what mic you're actually using as to how much gain you'll require. How long a cable are you thinking of? Will it have multiple stations? Will you want it to interface with any other manufacturers units?

G
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Old 4th September 2011, 05:50 AM   #8
ericj is online now ericj  United States
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NJM4556AL (SIP-8 version) is 67 cents each at mouser. Put a whole raft of them in your headphone distribution amplifier. Just make sure you stick a few uf of capacitance near the power pins of each one.

Did i mention they are unity-gain stable? Use one for gain and feed 10 of them for less than $10. It won't even be hard to wire. You could do it on stripboard. You could do 10 pair out of a mint tin.



if you already have the 4558, well, it will power one pair of headphones ok. most of the time.

Edit: fwiw NJM2068 is near the same power output as the 4556 with lower noise. for the same 67 cents.

Last edited by ericj; 4th September 2011 at 05:54 AM.
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Old 9th September 2011, 06:41 PM   #9
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Originally Posted by ericj View Post
Edit: fwiw NJM2068 is near the same power output as the 4556 with lower noise. for the same 67 cents.
I don't know where you got that from. Even according to the datasheets, the 4556 delivers nearly twice the output current and seems to have much lower output resistance.

Otherwise: agreed.
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Old 9th September 2011, 07:01 PM   #10
Vladco is offline Vladco  United States
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PhantomBox Chip not the only thing important for sound. Please do the search for grado clone (ra-1) or step up to amps on headwize (project area) or tangentsoft.org(very nice tutorials and amp). Of cause YMMW.
Vlad
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