Hi, I'm Nick

I've just built my first project - a small amplifier using a opamp TDA2003 (one channel so far).

It seems to work fine on my work bench - so I decided to expand the project and build :

1. The other channel
2. Power supply board
3. Simple pre amp

Now, I'm looking the 3 circuit diagrams wondering how it all connects together.

Do I just connect every point on each circuit board labelled "ground" to the metal box? Maybe bring all "ground tracks" to a central point - connected to the box - connected to earth mains ?

What if the preamp was in a different box? The RCA connection cable between the boxes has left and right ground wires ... connecting the boxes?

To complicate the issue - I made a mistake in choice of preamp design. It uses + and - 15 volts .. so that is the power supply I built. I forgot the amplifier tda2003 was only +15 volts.

Therefore I think I must choose another amplifier design for + and - 15 volts .... or have two different power supplies in the same box ?

Absolutely any advice would be helpful.

Thanks,
Nick.

 

Most likely the systems are not galvanically isolated, so it is usually an advantage to bond all to metal chassis, and earth ground.
Max.

 

You only need to connect one point to the chassis. All the other points are just tied together with a large bus wire.

All grounds are common among all the circuits you build that work together.

If you connect two boxes with RCA cables, then the cable shield (outer RCA contact) ties the two grounds together. But note that if both boxes use the same supply then there needs to be a ground connection (wire) from both boxes to the supply common.

You just need two supplies. You can share the plus supply between the preamp and the power amp. But note that if both

 

Thanks MaxHeadRoom,

I was just looking for confirmation that I'm on the right track - which I think you've done.

I'll finish the last board and connect it all up.

Nick

 

Since crutschow didn't finish his post, I think he was going so say

"Make sure that the zero volt return carrying large currents (from the power amp) is not the same wire as the zero for the preamp"

 

Since crutschow didn't finish his post, I think he was going so say

"Make sure that the zero volt return carrying large currents (from the power amp) is not the same wire as the zero for the preamp"

Actually it was a typo duplication from the previous paragraph. But you add a good point.

 

Thanks for your replies.

Perhaps it may help if I attach preamp circuit diagram. This is one channel, so the board has 8 points connecting to ground !

Suppose there is an OUT rca wire and an IN rca wire. Do these ground points not "connect to the box" at the Amplifier circuit board and the rca jack on the box wall ?

Same with the power supply board. It has 3 pins. +, - and ground. Is the connection to the box not at that point?

Why am I drowning in ground connections ?

I'll have to study this again in the morning.

Nick

 

All the grounds in your diagram should be connected on the board to either a ground plane or a large ground track.

One and one only lead should go from this preamp board to your designated ground point for the whole amplifier.

The negative terminal of the large power supply capacitor is usually used for this. You will be able to use the +15V for both power amp and pre amp.

One single wire should go from the power amp board to this designated earth point.
Do not wire the earth (zero) on the preamp directly to the zero on the power amp.

One single wire should go from the designated earth point to the metalwork of the case/chassis.

If your transformer has no centre tap you can obtain the small -15V supply from a second bridge and capacitor but with the cap positive connected to earth. This bridge and capacitor can be considerably smaller than the main +ve supply since the negative current requirement is tiny.

 

Thank you Studiot for patient explanation. I see what I have to do now.

I'm making the necessary changes to my preamp circuit board design.

I'll post my success (or not) in a day or two.

All I have to do now is get through the Saturday morning traffic here in Cape Town to get some missing components !

Nick