Thread: Class D amp
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N_Cook N_Cook is offline
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Default Class D amp

On 21/03/2018 22:17, Gareth Magennis wrote:

I'm trying to fault find this amp.

The IC's are IRS2092 0

It very, very, occasionally goes bad one side. (this is 2 amps configured
as bridged)
I have replaced the bad side IRS2092 into a socket, but the exact same
problem remains.

This is a real pain because it will run all day without the fault
so it is difficult to find out exactly what is going on.

I did eventually get to capture some scope data under the fault condition.
This is the output of both amps connected to an 8 ohm speaker.

It goes "boing, boing, boing", at a rate of just under a second.

Zooming in a bit, you see

A bit more you get

Zooming right in you get

The above screenshots are from the storage memory of the scope, so you will
get quantisation anomalies as you zoom in closer.

Here is a real time screenshot of both amp outputs behaving normally.

From the schematic, you will see that both amp's switching frequency is
adjustable via a preset. (not seen this before)
So both are pretty much free running, thus not synced together at all.

However, if you adjust each to be close to the required 333kHz, they do
actually sync together, hence the nice synced screenshot.
(presumably this is from switching spikes via the power supplies)
They don't care in normal operating conditions if they are synced or not.

I have changed ALL of the filter caps on the amp outputs, including the
on the HT rails, thinking it might be an output filter problem, not the
The identical fault still occurs.

I'm still very much a beginner on Class D, but this kind of thing is
becoming increasingly common, and I need to get my head around it.



Are both amps, audio speaking , in phase or deliberately out of phase
live Yamaha Stagepas (reduces the sag on reservoir caps on peak demand)