# Bypass Capacitors quick question?

#### Tony Elliott

Joined May 8, 2015
144

Hi,
I am using a mains supply +/- 12 so I don't need the bypass capacitors right?

#### ErnieM

Joined Apr 24, 2011
8,043
Wrong.

The caps shown should be thought of as a minimum, a starting point. That is what worked for the designer on his board, your board may need more.

Seems these were drawn without and hints as to where to place them. I would start with the 10 uf where the power enters the board. I would put a pair of the 0.1 caps with them, and another pair on each op amp. You need more than the schematic implies but here more is usually better and rarely if ever hurts.

#### crutschow

Joined Mar 14, 2008
24,988
Never skimp on bypass capacitors.

#### Papabravo

Joined Feb 24, 2006
13,746
Bypass capacitor arrangements work best when you have several values in parallel. The higher values ( >1 μF) typically supply transient current demands of the adjacent chips, while smaller values (<= .1 μF) supply a path to ground for high frequency transients. Putting the three values in parallel is different than just having one capacitor of the equivalent value. eg 1 μF || 0.1 μF || 0.01 μF behaves differently than a single 1.11 μF capacitor assuming such a thing was available.

You can work out the reactance of a capacitor at various frequencies via

$$X_C=\frac{1}{2\pi f C}$$