Class D amp

Hi,

I'm trying to fault find this amp.

formatting link

The IC's are IRS2092

formatting link

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 occurring, 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.

formatting link

Zooming in a bit, you see

formatting link

A bit more you get

formatting link

Zooming right in you get

formatting link

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.

formatting link

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 ones on the HT rails, thinking it might be an output filter problem, not the amp. 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.

Cheers,

Gareth.

Reply to
Gareth Magennis
Loading thread data ...

I hate those things. (figure of speech)

Exactly what happens to the speaker output when it fails ?

Reply to
jurb6006

Analogue amps do similar things when their PSU caps go bad. Might be an area to look at.

NT

Reply to
tabbypurr

I hate those things. (figure of speech)

Exactly what happens to the speaker output when it fails ?

*************************************

This:

formatting link

Total sweep time across the screen here is 2.4 seconds. I can only describe it as sounding like "boing, boing boing", with a boing every 0.8 seconds.

It is not VERY loud at all, nothing that would damage the speaker as far as I can tell, but this screenshot is the unfiltered output of the amps, not the filtered waveform the speaker sees. There are a whole bunch of inductor/cap/resistors between the amps and speaker.

Gareth.

Reply to
Gareth Magennis

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

Reply to
N_Cook

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

******************************************

They both share the same PSU rails, not like Stagepass.

The PWM signal to one amp input is inverted, making this standard bridge mode.

PSU is an SMPS.

Gareth.

Reply to
Gareth Magennis

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.