[sdiy] Decoupling caps?

[patchell]

charlie lamm wrote:

> I have read often that when setting up PCB's one
> should always use decoupling caps (.1uF or so) for
> IC power pins.

    Bypass Caps have a #1 priority when I lay out a PC board.  I may go a
bit overboard, but one bypass cap per power supply pin is my general rule
of thumb.

>
>
> 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?

    A single sided board will make your layout duties a little more
difficult.  But the bypass caps are fairly important.

>
>
> 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).

    Actually, bypass caps are more important for the TL082.  Bypass caps
will not solve any problems created by poorly regulated power supplies.
The bypass cap is mainly to keep the TL082 from oscilating.

>
>
> Maybe I can put some decoupling caps away (bigger? 10uF?) from the IC's
> where there is a bit more room on the board?

    Bigger is not better...the bypass caps are for high frequency signals.
You want them as close as posible to the IC power supply pins.
Electrolytic Caps (or Tants) are in general not very good at the higher
frequencies.

>
>
> Or should I just tweak the design to figure a way to fit these in?

--
 -Jim
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