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Class D Switching Power Amplifiers and Power D/A conversion

Multiple AMP boards and PSUs in one case, what about common ground plane?
Multiple AMP boards and PSUs in one case, what about common ground plane?
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Old 18th January 2019, 04:43 AM   #1
Cradle22 is offline Cradle22  Germany
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Default Multiple AMP boards and PSUs in one case, what about common ground plane?

Hi,

since I got no answers inside some other threads I ask this kind of question again.

I have four amplifier boards (three of the same type (TPA3255) with three single rail SMPS, one (IRS2092) with a dual rail SMPS)

The three single rail SMPS are mounted isolated from the chassis.
The dual rail SMPS has an aluminium casing which is not connected to the ground plane from the output of the smps.

However, all four amplifier boards share the ground plane through the mounting holes.

I still have (other) problems to get everything up and running (two TPA3255 boards are kind of "dead", LEDs turn on, but no sound at the speaker output).

But I do wonder if I will have to change the way I mount those amplifier boards to the chassis in a way that not all four ground planes are tied together (remember, I also use four SMPSs).
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Old 18th January 2019, 05:59 AM   #2
Turbowatch2 is offline Turbowatch2  Germany
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Switched amps should be syncronised when feed by one power supply. You can read this in the data sheet fron TI and others. Is very often ignored with good results, the china boards often hav a diode in the + feed, that may work too.
But with one SMPS per amp you donīt have to care.
For the rest, there is only one way to find out: Get all single parts running and then carefully combine them in your case.

Donīt fit not or half functioning parts!!! Repair and test, if not 100%donīt even think about fitting them!

Basicaly this is not different from using 4 or five amplifiers in one room with one signal source. So where is the problem?

First make a dry build, so you know how to group the boards in the case. Inputīs away from power lines, etc...
Then chose a single master ground, not connected to the chassis, only for audio.
Next wire the first amp. Test.OK? Next amp, test, amp, test...
Test it in the way you intend to use it, like connected to a pre-amp or active crossover. You will instandly hear when you do something wrong!

In the end you want to put the 230vAC earth to the chassis. Chances are high, if any signal ground meets it, you will have first class power line hum. Dont think you have to connect these two!

So dont! Sometimes, connecting ground and earth with a R C combination will make things quiet.
Wires have to be twisted and placed with some common sense. The strenght of a magnetic field emitting from a wire may be very loud in one position, then, only moved by a few milimeters, be dead silent.
Be carefull not to make connections by mistake. Measure resistences first, then switch on. Donīt work at parts under voltage. Power supplies store enough energy to blow up whole boards! Even whithout AC present!

There are normal rules, that have been followed a million times, with perfect results. If you ignore them, you will suffer. Non proīs often invent funny rules about "what is allowed by VDE" and "has to be done" which results in incredible nonsense. In Germany anyone wants to live by the law, even if he does not understand how to handel it. Your build in policeman. Genetic problem.
Oh, common faultīs: Donīt connect RCA sockets to a metall chassis and
you only have to connect the screen of a signal cable to ground at one side.
All signal grounds to one point, no exceptions! If you know all of this already, congratulations!

In the end, the ground/ earth configuration that works is the "right one". Usually this automatically compliese with federal rules.

The AC and metall case of your SMS should be connected to the (metall) case of your multi amp. The amps should make no contact trough screws with the cassis, use insulation washers. But I might be wrong, you sure will find out.


















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Last edited by Turbowatch2; 18th January 2019 at 06:09 AM.
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Old 18th January 2019, 10:06 AM   #3
Cradle22 is offline Cradle22  Germany
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Thank you for your answer. I have built about 15 to 20 amps so far, but each one of them powered by a single PSU, and I did put the mains earth together with the signal ground on the chassis, without any ground loops at all (never had to install a ground breaker, like described here at ESP.

Sadly I did not "measure" the mounting holes of the amp boards prior to planning the layout and actually building this thing (see Image).
So, in order to seperate the ground planes from the amp boards I have to come up with a complete different mounting solution...
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