[sdiy] NE542 query

[Brock Russell]

Bob,

You don't have bad parts. They self bias to 1.4 V. If you have app note 
190, read the section on biasing and look at Figure 3. There might be an 
error in the biasing formula. I recall having problems with this, but that 
was 15 or 16 years ago and the old brain isn't working so good tonight.

Brock


At 03:51 PM 4/20/2006, you wrote:
>Anybody ever designed with this.  I think I asked a while back but I 
>pulled out an old design of mine that got flustered today...and I see 
>why.  I had followed the idea in a diagram in the Signetics manual which 
>showed just hooking a .1uF cap to the non-inverting input as it is a 
>single sided op amp design which is supposed to self-bias that leg to 
>somewhere mid power supply rail.
>Unfortunately on a 12V system I rather get it at about 1.5V there.
>Adding a pull up resistor to the non-invert....you can get maximum of 3V 
>and if the resistance gets below probably 3K or something it just goes to 
>ground on the output.
>
>All the chips I have seem to do this.  Did I just get a bunch of 
>mismanufactured chips that soaked all this time away from me then 
>or...??  If anyone has a 542 chip they've designed in this way with I'd 
>love to hear about it obviously. -Bob