570/571- vs 572 Was RE: [sdiy] Automatic gain correction for Overdrive

[Batz Goodfortune]

Y-ellow Florian n all.

>Thanks for the many replies!
>
>I found an application note to the proposed NE570 circuit here:
>
>www-eu4.semiconductors.com/acrobat/ applicationnotes/AN175.pdf
>
>Looks quite usable, I am going to try this circuit as soon as possible
>(although the NE572 is a rather expensive chip, at ~6$)

The 572 is leaps and bounds ahead of the 571. In fact I would go so far as 
to suggest steering clear of the 571 entirely if possible. But! It should 
be noted that the 572 is a bugger to use. It doesn't always do what it's 
told. Converting from a 571 circuit could prove frustrating. The 571 has a 
single timing element (A cap to ground.) Where as the 572 has both an 
attack and decay timing cap that can be made variable if need be. But it's 
hard to get just right.

The 571 is a good noise source. It was designed for telephone systems and 
probably isn't good to use outside of that. I've built several Noise 
reduction units around both chips and whilst the 571 works in this context, 
it can often defeat the purpose with it's own noise. The op-amp is lousy. 
Really truly awful. The 572 gets round this problem by not having one. You 
need to use an external Op-amp of your choice. However if a single ratio 
compander circuit is OK you COULD use a 571 with an external op-amp. It's a 
bit tricky but doable. Although the rectifier is hard wired in one mode or 
the other. Which makes it problematic.

The cost trade off would probably be in space with the 572. Since the 
circuit contains all of the control circuitry and the gain cell, you only 
have to supply the op-amp. This means you don't have to lay out and align 
all these elements which would be significantly larger and probably wind up 
just as expensive. However with a more discrete design you have the 
opportunity to taylor the circuit to work exactly how you need it too.

And remember that both of these chips are dual circuits. So if you only 
need one, you're going to waste half of it. You might have to find 
something else you want to do with the other half.

Hope this helps.

Be absolutely Icebox.

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