questions from a newbie (Op Amps again)

[KA4HJH]

>Just arbitrarily using a faster op-amp is a recipe for oscillation (and noise)
>A phaser I designed using a (yuck) LM324 and upgraded to a TL084, oscillated
>ultrasonically because of the higher gain at high frequencies... Drove the dog
>nuts !!!  I almost left it that way TO drive the dog nuts... I hated that dog
>!!!!

Also a good way to fry tweeters and other components without ever 
realizing why. If you don't have a dog or a bat around, that is. I've 
heard of output transistors in a amp running red hot with no signal 
in--turned out there was some high-amplitude ultrasonic oscillation 
somewhere in the circuit!


>  > >Output Current... Can it drive the load you will be using ???
>>
>>  I have never looked at this spec. Every thing I've done so far has had a
>>  reasonable input impediance. I hooked the output of an LM324 to a 10Hz low
>>  pass filter today and it seems to be working okay - I'm not sure what the
>>  impediance is - I forgot to check - should be on the order of 100 to 200
>>  ohms.
>
>The LM324 (yuck) has a nasty trait... which is why I look at output drive
>current. It has
>different source and sink currents... could be a problem in symmetrical
>circuits (like limiters) or if you are driving a capacitive load. 
>Again... you
>got to watch your @ss here.

A lot of heaphone amps have been built around the 5534 apparently 
because it has the necessary output specs...


>I think its time for an OPAMP primer here... whaddya think???

Go for it. They're rehashing the subject in Circuit Cellar right now. 
Apparently a lot of digital engineers didn't pay much attention in 
class to analog design and they just slap whatever old op-amp in 
there.


I find it difficult to solder and answer email while watching my @ss... 8^)

-- 
Terry Bowman, KA4HJH
"The Mac Doctor"