PCB for active filters - supply question

[GrzMiL]

Hi
I'm about to finish PCB for 3 way active filters and because I'm newbie at makeing PCB, I'm not sure if i should use some capacitors between supply's rails and GND on the board.
The length of trace from supply input to last IC (ne5532) is about 6''/15cm (66/100 mils wide).

Should I use caps close to each opamp (if yes what capacity ) or a few bigger on supply rail in equal distance form each other or just two big at the +V/-V input.

Supply input is on the top of the board

P.S. Should i cover all the free space with copper and connect it to ground in one point or isn't it necessary.

[BWRX]

Definitely make provisions for 0.1uF decoupling caps from the supply rails to ground as close to the supply pins of the chips as possible. Some also like to use decoupling caps from rail to rail too.

Filling the empty space with a ground pour might not be a bad idea. It probably won't make much of a difference at the frequencies the circuit will be dealing with.

[jackinnj]

Originally posted by BWRX
Definitely make provisions for 0.1uF decoupling caps from the supply rails to ground as close to the supply pins of the chips as possible. Some also like to use decoupling caps from rail to rail too.

Filling the empty space with a ground pour might not be a bad idea. It probably won't make much of a difference at the frequencies the circuit will be dealing with.

it's not the audio range frequencies which should concern us -- it is the high frequency from switching power supplies, electromagnetic interference (from appliances), radio frequency interference -- you don't want these spurious emissions coupling into a low level board -- such as a filter.

Ceramics are preferred. If you are in the least bit daring consider using surface mount, 0805 devices (smaller than this becomes impossible to solder in my old age The surface mount caps are inexpensive and not difficult to solder if you just tack one end down first. They can be mounted very close to the pins of the IC you want to decouple.

I have had success with "ground pour" -- an attaching the ground plane at the star ground.

[Elso Kwak]

IMHO ceramics sound bad in analog circuits, even as bypass caps.

[BobEllis]

It is a good idea to have some largeish decoupling capacitors on the filter boards - a few hundred uf is fine.

It is absolutely essential to have small (100 nf) decoupling capacitors as close to each opamp as possible.

Not to discourage your efforts, but have you seen the Active Filter Group Buy ?



I am also running a power supply board group buy
Here

[GrzMiL]

I forgot to attach file so that you could see what i was talking about.

Sugestions are:
1. 100n caps at every IC's supply pins - necessary !
2. Add a bigger cap (about 100-200uF) at voltage input on the board
3. Fill free space with ground and connect it to ground at "star point"

2 more questions

1. Is there any problem with connecting decoupling caps to ground that is used by signal (v.ery wide ground trace - 100-254 mils)

2. The signal path from buffer output to filter stages is quite long.
Is that a problem ? (marked on green in image)

[GrzMiL]

BobEllis

thx for proposition, but i've already designed the PCB and have a lot of PCB ( i don know how is called the board with copper clad).

I've already made some PCB using lasser printer, paper and iron method. And it looks very good so i stay with my project.
Moreover this PCB exactly fits my needs and it'll give me a lot of satisfaction if it works correctly

[BobEllis]

GrzMiL, no offense taken. I understand the joy of creation. Good luck on your project.

I got lucky and Jens felt like designing a board that met my current and foreseeable future needs. By having it made professionally i got plated through holes. soldermask, silkscreen and I didn't have to drill all those holes.