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Old 13th September 2008, 09:05 PM   #1
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Default Chipamp shorting at high volumes.

My chipamp has been working well for a couple months but as a precautionary measure I have been using the the light bulb in series with the mains.

Today, something weird happen. I was turning up the volume higher than usual and suddenly I heard a funny Buzzzzz noise coming out from the speakers and the bulb lightened up for a moment.

Evidently there is a short circuit, what I do not understand is why this is shown only at high volumes.

Comments appreciated .

Regards

Antonio
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Old 13th September 2008, 09:38 PM   #2
Puffin is offline Puffin  United Kingdom
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Isn't the bulb in series restricting the amount of juice going to the live side of the tranny?
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Old 13th September 2008, 09:43 PM   #3
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It could also have something to do with the "spike" protection,or other protection circuitry kicking in.
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Old 13th September 2008, 09:44 PM   #4
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Edit: Thanks Pufin

Probably. I do not know.

Could the lightbulb be the cause of the problem? Now I do not dare to remove it.
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Old 13th September 2008, 09:47 PM   #5
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Quote:
Originally posted by DigitalJunkie
It could also have something to do with the "spike" protection,or other protection circuitry kicking in.
I am using CarlosFM LM3886 design and I did not add any extra protection circuit.
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Old 13th September 2008, 09:56 PM   #6
Puffin is offline Puffin  United Kingdom
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The Spike protection is contained in the chip as standard. Have you tried a normal mains lead? It seems to me that if you are limiting the juice to the tranny, you will not get full power when the volume is turned up. The amp has been running for some weeks now and appears to be stable, so time to ditch the light bulb lead me thinks.
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Old 13th September 2008, 10:02 PM   #7
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A short-circuit would already show at very low volumes.

After several months of operation there is no need for the light bulb anymore.

Be aware that the light bulb not only limits the current during faults, but also during operation. You have probably reached that limit. As a result the light bulb lights up, the voltage at the IC dips, the undervoltage protection sets in, lights bulbs goes dark, voltage and current go up, light bulb lights up again, etc. result is hum from the speakers. Take the light bulb out of the circuit and rely on the SPiKe protection system. You will probably have no further problems.

If however a hum or buzz with a crackling character comes from the speakers, turn down the volume. Reasons for that could be
  • - speaker impedance too low for the amp
    - speaker efficiency too low for your sound pressure level taste
    - power supply too weak for your combination of amp, speaker and sound pressure level taste
    - listening level too high to be healthy
    - and the less pleasant (and less likely) reasons: DC or oscillations that use up part of the amps power and leave less for the speakers
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Old 13th September 2008, 10:11 PM   #8
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Puffin and Pacific.

Many thanks.

I will remove the light bulb and proceed carefully with the volume levels and will check dc offset. Ah! and will use some crap speakers during testing.

Regards

Antonio
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Old 13th September 2008, 11:59 PM   #9
stcboy is offline stcboy  Saudi Arabia
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Hi A.Sanchez,

Have you try to removed the bulb in the normal operation? See if you still have that buzzing sound w/out the bulb.In my opinion your psu current is not enough when you use that bulb as it limit on your supply line.

Regards
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Old 13th September 2008, 11:59 PM   #10
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I think there is something wrong with the power supply

maybe the powersupply can't produce enough power to keep up
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