Re: [sdiy] Speaking about the LM324...

[jhaible at debitel.net]

First of all, you can be sure that an EQ that contains LM324's was designed
like that for one *single* reason: To be as cheap as possible.

(Paul Schreiber has recently posted a nice anecdote about the use of cheap
components in commercial products, despite every customer scratching his
head why they cut corners on the wrong place. Care to crosspost this
to synth-diy, Paul?)

Now that you have these slow chips in your EQ and want to replace them,
I'd ask myself two questions:

(1) What else do I have to change? 
A better opamp will most likely need better decoupling, so be prepared
to add some bypass caps.

(2) Do I want to change the sound?
Only do it if you don't like it as it is. There are circuits where *I* would
upgrade opamps without hesitation (your EQ being one example),
but others where I would not do it. (741 in Oberheim SEM-VCF).
Just my opinion - "good" sound is very much a matter of taste.

(3) Common mode range
Most JFET opamps will go crazy if an input goes near its negative 
supply voltage. The 324 will handle this easily. So make sure
that this does not happen in your circuit, not even temporarily 
at overload, before you put in a TL074 or something like that.

JH.


I have a very nice 19" parametric EQ using the LM324. But I recently thought
about changing to a better tybe because the LM324 is noisy.

Is there anything special on this OpAmp or can I use a generic jfet type as
replacement?

Thanks,
	Nils