[sdiy] Decoupling caps?

[Theo]

Best is to do both:
10uF where the power enters the board,
100n close by the ICs.

The  100n decoupling caps close to the ICs (BTW read close as
_really_cozy_ )
help to prevent nasty oscillation behavior from the opamps.
Oscillation problems is the main reason to put the caps there, not the noise
level.
IMO those caps are mandatory!

And really, the decoupling is not what makes the difficult tracks or eats up
the board space.
For a easy and clean layout:
Run the power rails under the ICs and GND at some distance on the outside of
the ICs.
When decoupling _between_  rails the decoupling cap sits directly at the
"head" of the IC.
This decoupling method takes the least components and space.
Also there are no extra traces involved = no blocking.
Although  you may need a occasional jumper to jump over the power rails you
can usually do this with an resistor or other component.

HTH
Theo


----- Original Message -----
From: charlie lamm <charlie at www2.charlielamm.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, January 10, 2003 6:35 PM
Subject: [sdiy] Decoupling caps?


> I have read often that when setting up PCB's one
> should always use decoupling caps (.1uF or so) for
> IC power pins.
>
> I am designing a PCB for the ASM-1 VCO.  I am limited
> in board space and want to make a single sided board so
> I can press-n-peel.
>
> Now, I know this may be too general a question, maybe too general, but,
> how important are the decoupling caps in a circuit like this?
>
> I assume decoupling would be extremely important in OTA's,
> since they seem to react badly to poorly regulated supplies....
> but with TL082's etc?  Can I get away with not using them
> and still have the VCO sound decent (in tune/not too badly distorted or
> noisy).
>
> Maybe I can put some decoupling caps away (bigger? 10uF?) from the IC's
> where there is a bit more room on the board?
>
> Or should I just tweak the design to figure a way to fit these in?
>
>