LM4562 opamp crackling when trying to drive headphones.

50AE · 07:01 PM

Hi,

I've got a problem. After modding my sound card X-fi music with an LM4562 opamp, it seems the sound gets crackling after a certain point of load. I'm using 24 ohm HD201 headphones.
On lower loads, it isn't apparent, but when I get the volume after certain point, a crack occurs wich is synchronous with the frequency. It means if I launch 30Hz, 30 cracks will occur. While the crackling is somewhat gentle, it is still disturbing for a guy who likes pure sound.
It does on 32 ohms HD433 headphones at a higher volume, but not on the speakers.

I suspect it could be an overloading issue. But should it crack this way?

I am currently saving to make a headphones amplifier.

5th element · 6th October 2011, 09:44 PM

The crackling sounds like it could be the opamps protection circuitry coming into play which is more likely to occur at the amplitude minimum/maximums.

The opamp will inherently limit at +-23mA which would correspond to ~ 0.5 volts peak on the HD201s, this isn't an awful lot, but a 24 ohm load is pretty hard to drive as headphones go. The LM4562 is simply not suited to this role.

That being said you don't specify which X-fi card you are talking about. Does the opamp you replaced drive the headphones directly? Or is there a stage after the opamp that then drives the headphones?

50AE · 6th October 2011, 10:14 PM

The sound card is creative X-fi music. Judging from my route tracing, the opamp drive the headphones directly.

5th element · 7th October 2011, 12:33 AM

Quote:

Originally Posted by 50AE

the opamp drive the headphones directly.

What did the card use before you changed the opamp? Regular opamps aren't designed to drive headphones and especially not ones with such a low impedance as the HD201. It makes sense that you can increase the volume further with the HD433s as they are easier to drive.

nelsonvandal · 7th October 2011, 06:17 PM

LM4562 just isn't up to the task driving low impedance headphones. I've tried it. You need a buffer or use another opamp.

jaycee · 8th October 2011, 05:27 PM

The original was probably a 4556 or an 5532, these are suitable for driving headphone loads (though probably only 32 ohms and higher) and the LM4562 is not. Most soundcards do a crap job of driving headphones anyway - a buffer is well worth it

50AE · 9th October 2011, 04:36 PM

Thank you guys, your posts confirmed it. Yes, the original opamp was a 4556. I'm planning a headphone amp.

6th October 2011, 06:58 PM	#1
50AE diyAudio Member Join Date: Jul 2011 Location: Sofia, Bulgaria	LM4562 opamp crackling when trying to drive headphones. Hi, I've got a problem. After modding my sound card X-fi music with an LM4562 opamp, it seems the sound gets crackling after a certain point of load. I'm using 24 ohm HD201 headphones. On lower loads, it isn't apparent, but when I get the volume after certain point, a crack occurs wich is synchronous with the frequency. It means if I launch 30Hz, 30 cracks will occur. While the crackling is somewhat gentle, it is still disturbing for a guy who likes pure sound. It does on 32 ohms HD433 headphones at a higher volume, but not on the speakers. I suspect it could be an overloading issue. But should it crack this way? I am currently saving to make a headphones amplifier. Last edited by 50AE; 6th October 2011 at 07:01 PM.

6th October 2011, 09:44 PM	#2
5th element diyAudio Member Join Date: Oct 2002 Location: England	The crackling sounds like it could be the opamps protection circuitry coming into play which is more likely to occur at the amplitude minimum/maximums. The opamp will inherently limit at +-23mA which would correspond to ~ 0.5 volts peak on the HD201s, this isn't an awful lot, but a 24 ohm load is pretty hard to drive as headphones go. The LM4562 is simply not suited to this role. That being said you don't specify which X-fi card you are talking about. Does the opamp you replaced drive the headphones directly? Or is there a stage after the opamp that then drives the headphones? __________________ What the hell are you screamin' for? Every five minutes there's a bomb or somethin'! I'm leavin! bzzzz! Droggon Attack!

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6th October 2011, 10:14 PM	#3
50AE diyAudio Member Join Date: Jul 2011 Location: Sofia, Bulgaria	The sound card is creative X-fi music. Judging from my route tracing, the opamp drive the headphones directly.

7th October 2011, 06:17 PM	#5
nelsonvandal diyAudio Member Join Date: Nov 2006	LM4562 just isn't up to the task driving low impedance headphones. I've tried it. You need a buffer or use another opamp.

8th October 2011, 05:27 PM	#6
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	The original was probably a 4556 or an 5532, these are suitable for driving headphone loads (though probably only 32 ohms and higher) and the LM4562 is not. Most soundcards do a crap job of driving headphones anyway - a buffer is well worth it

9th October 2011, 04:36 PM	#7
50AE diyAudio Member Join Date: Jul 2011 Location: Sofia, Bulgaria	Thank you guys, your posts confirmed it. Yes, the original opamp was a 4556. I'm planning a headphone amp.

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