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.
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:
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?
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?
The sound card is creative X-fi music. Judging from my route tracing, 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.
LM4562 just isn't up to the task driving low impedance headphones. I've tried it. You need a buffer or use another opamp.
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
- Status
- Not open for further replies.