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Old 30th May 2016, 04:12 AM   #1
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Default Iraud 350 problems :(

Hi everyone.

I just built my iraud350 amplifiers and I have run into a problem.

One of the amplifiers runs the 95v side at 110v. This makes the caps very unhappy . They draw lots of current and get very hot. I didn't notice it at first and one of them got so hot it popped. Poor cap.

Anyways I have lots of replacement caps so it's not a big deal.

Does anyone have a schematic on these amps or have any idea why it would do this?

One of the amps works perfectly with 55v on one side and 95v on the other.

I am running it from a 1000va toroid at 45-0-45v. It is over 100v even if I run the board at 25-0-25v using a variac.

Perhaps I just got a bum board

Any ideas?

Thanks
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Old 30th May 2016, 05:32 AM   #2
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Ok so heres an update.

Each side should be at 55v.

One of my amps run at 55v on both sides. However one runs at 55v and 110v.

When I remove the load they are both at 55v.

I am driving 16ohm electrostatic panels in parallel for 8ohms.

Seems they would be ok with 8 ohms but I know electrostatic speakers are weird loads.

Maybe this is a load problem? Either way... Can it be fixed?

Thanks
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Old 31st May 2016, 12:20 AM   #3
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Quote:
Originally Posted by JazmynFox View Post
Hi everyone.
.

I am running it from a 1000va toroid at 45-0-45v. It is over 100v even if I run the board at 25-0-25v using a variac.

Thanks
45 volts AC will give 63 volts DC when rectified.

Are you sure your zero volts is connected to the amp ?
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Old 31st May 2016, 12:40 AM   #4
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I am running it at 100v primary so I'm getting more like 35-40v.

I have replaced all the transistors and capacitors with no change. It must be a problem on the irs2092 board.

I contacted the seller for a new board.

Thank you
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Old 31st May 2016, 10:53 PM   #5
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The only time I had problems with class d power supply was when I had trouble with bus pumping.
Low frequencies into the class d amp pump back dc into power supply raising power supply voltage.

Are you testing your amp with a sine wave or are the voltages you are getting with no input signal ?
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Old 31st May 2016, 10:56 PM   #6
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I get the voltages with no input signal at all


I thought it might be bus pumping but I'm not really sure at this point.

Thank you
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Old 1st June 2016, 09:16 AM   #7
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Is there any DC at the output ? What is the DC resistance of the ESL step-up transformers ?

Regards

Charles
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Old 6th June 2016, 04:13 AM   #8
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Yes there is DC offset.
Poor output transistors?

The resistance of the primary from the multimeter is 0.3 ohms. Very high step up transformer (1/60) or more for the woofers.

Thanks
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Old 6th June 2016, 07:41 AM   #9
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There is no lower frequency than DC, casually speaking.
DC at the output will definitley lead to bus pumping if the DC current is higher than the idle current from the opposite rail. The very low DC resistance of your step-up transformer doesn't help it either.
For a quick and dirty test I would put a large cap in series of the primary in order to see whether the bus pumping is gone and if you can play music.
If that is the case the cause of the DC offset has to be found. Maybe it is even within limits of that amp. In this case some DC trim has to be amended.

Regards

Charles
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Old 6th June 2016, 11:21 PM   #10
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I calculated the size of the capacitor needed to achieve 20hz to be about 10,000uf.

That might be hard to find in a non polarized capacitor. .

Perhaps these speakers just aren't quite right for these amps. Although one amplifier handles it fine :/.

Would a 10,000uf 100v polarized capacitor work? I have a feeling the polarity could be a problem with AC. Many polarized electrolytics are very unhappy with AC.

I might just have to wait for the new module to get here. It's possible I just got a dud.

Another idea is finding a 1/1 output transformer and using that to block DC on the output.

Not really sure.

Thanks everyone.
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