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-   -   njm4556 op amp (http://www.diyaudio.com/forums/chip-amps/67530-njm4556-op-amp.html)

crippledchicken 8th November 2005 04:54 PM

njm4556 op amp
 
i have the njm4556 for headphone output on my adcom GFP 565 preamp which the manual states 100 ohm impeadance but, the radio shack phones i just purchased have 60 ohm impeadance? are there better choices for op amp? or maybe add buffers such as LT1010, or buf634t which i have both of? if buffers would be best, anyone know of any Links where i could find out how to apply the buffers? thanks, crippledchicken :)

richie00boy 8th November 2005 05:01 PM

The BUF634 datasheet is very good and explains how to boost op-amps with it.

Any normal op-amp would be struggling to drive less than 600 ohms. I think OPA134 series will drive headphones OK directly. You'd have to check the datasheet for the NJM to confirm it's driving ability. You need to see what voltage the chip is running from then check the output current limit graphs.

crippledchicken 8th November 2005 05:06 PM

Quote:

Originally posted by richie00boy
The BUF634 datasheet is very good and explains how to boost op-amps with it.

Any normal op-amp would be struggling to drive less than 600 ohms. I think OPA134 series will drive headphones OK directly. You'd have to check the datasheet for the NJM to confirm it's driving ability. You need to see what voltage the chip is running from then check the output current limit graphs.

hi there, the njm4556 has lm78/79 15v. regulators driving it. could the opa 2134 also, maybe work since it's a dual as i have some of them? thanks

richie00boy 8th November 2005 06:29 PM

15V supply is pushing it. Yes the OPA134 series will work, whatever fits your board. However the NJM chip may be totally fine, just check the datasheet :)

crippledchicken 8th November 2005 07:12 PM

Quote:

Originally posted by richie00boy
15V supply is pushing it. Yes the OPA134 series will work, whatever fits your board. However the NJM chip may be totally fine, just check the datasheet :)
Thanks! Will Do

anatech 8th November 2005 07:37 PM

Hi crippledchicken,
You will find the 4556 is used in almost every product without an amplifier to drive headphones. It was designed for this.

If you want better performance, I would suggest building an outboard unit. There is only so much you can do with a single op amp to get rid of heat. Then you can build better power supplies and use the better op amps to full effect.

-Chris

crippledchicken 9th November 2005 12:24 AM

Quote:

Originally posted by anatech
Hi crippledchicken,
You will find the 4556 is used in almost every product without an amplifier to drive headphones. It was designed for this.

If you want better performance, I would suggest building an outboard unit. There is only so much you can do with a single op amp to get rid of heat. Then you can build better power supplies and use the better op amps to full effect.

-Chris

hi anatech i think youre right, i have seen this chip several times used to drive headphones. i think i'll be checking into building an external amp. Thanks, crippledchicken


:)

Dominique 9th November 2005 09:34 AM

There are certainly better performing op-amps out there... (ok, I didn't look at the NJM4556 datasheet yet :rolleyes: )
Do you need a DIP-8 or SO-8 package?

crippledchicken 9th November 2005 02:01 PM

Quote:

Originally posted by Dominique
There are certainly better performing op-amps out there... (ok, I didn't look at the NJM4556 datasheet yet :rolleyes: )
Do you need a DIP-8 or SO-8 package?

hi Dominique, what i need are the DIP-8. i have, opa2132, opa2134, opa2604, lm6172,, AD826, LT1364, as well as the LT1010, and BUF634T buffers on hand if any of these could be implemented for better performance? thanks for any ideas, crippledchicken

:)

Dominique 11th November 2005 12:56 AM

I had in mind to simply replace the op-amp for a stronger one, but after checking my gathered data, I couldn't find op-amps in a DIP package better than the NJM4556 (low impedance output), but only in SOIC and TO packages. Most of them are high speed, so it's not clear if they would work fine without tweaks in your existing circuit anyway.

Either you simply try your new headphones and listen if there's more distortion, build an outboard unit like anatech proposed, add a little pcb with a buffer in your preamp (then you could replace the NJM4556 for a weaker, but better op-amp), or use a SOIC op-amp with a SOIC to DIP adapter (but it's not guaranteed to work fine in your existing preamp (because all those strong SOICS on my list were high speed :( )

Sorry I couldn't be of much help!
Cheers,
Dominique


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