Class A bias 4556 20mA...

[kasra]

In between other projects I built a small OP based headphone amp using 4556ad to drive headphones directly(32R). Witch dcservo and class a bias.

By mistake using wrong value, the bias went up to 20mA with +-15V rails.
Since the OP gets quite hot I added a small heatsink, but it seems to work quite good.

Anyone tried that high bias with opamps driving cans directly? Any downsides using that high bias current?

The ground is TLE2426 splitted and buffered with a OP27GP.

 

[__redruM]

One downside is wasted battery life. Unless ofcource it's wall powered. It might also limit OPAMP lifespan, since it's getting hot.

Which amp design?

 

[Dreamslacker]

Yes, I've done 20mA on opamps before. I just needed to put large heatsinks on the opamps to cool them (more so because the average room temperature is 28'C and above).

See the following image:

 

[kasra]

Nice, that heatsink seems a little overkill? Mine is a smalish halv square inch one. Anyways, the sound is really nice, and it has more power than xcan v2 driving grados

Regarding the life length its not really important, since the op just costs a couple of $$$.

 

[breez]

kasra:

Could you provide me with the schematic if possible? My current plan for the headphone section of my speaker amp is just the basic non-inverting op-amp config with the 4556, but I'd like to try something better with the parts in my hand right now.

 

[kasra]

breez&redrum:
This is a noninverting as RA-1 clone, but without input capacitor. Insted it has a DC-servo. Also Class A bias. Supposed to be 5mA.

For using with MS2 fatboys ive changed
R2,R12: 100k
R5,R15: 4.7k

And im running with +-15V now.

 

[Dreamslacker]

Quote:

Originally Posted by kasra Nice, that heatsink seems a little overkill? Mine is a smalish halv square inch one. Anyways, the sound is really nice, and it has more power than xcan v2 driving grados Regarding the life length its not really important, since the op just costs a couple of $$$.

Not quite... As I've mentioned, temperatures here are higher than in the States. I didn't want the opamps to operate too hot cause that will have a negative effect on the sound.
Without the heatsink, the opamps will go into thermal shutdown in about 1/2 hour.