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Old 10th December 2010, 04:06 PM   #1
Ted205 is offline Ted205  United Kingdom
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Default SPiKe™ protection

Hi guys

Does anyone know if the lm3886 SPiKe™ protection causes a buzzing/fuzzing sound when engaged.

I'm getting this aswell as increased heat from the chip but i'm not sure if its spike protection of a current/grounding issue.

any opinions
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Old 10th December 2010, 05:51 PM   #2
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Is this happening without signal? If so, it sounds more like oscillations.
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Old 10th December 2010, 07:05 PM   #3
LAJ is offline LAJ  United States
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I think with SPIKE it just shuts down. But I have seen many of those chips blown up. Is it getting hot? Yeah, I'd scope out your supply rails and look for oscillation. If you don't have a scope, I'd just add some more capacitors on the rails. Also layout of the circuit will make it oscillate if your output is too close to the input. And, lastly, do you have any DC on the output?
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Old 10th December 2010, 08:03 PM   #4
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If you take a look in the documentation, SPIKE actually changes the waveform to reduce the power output, and does cause a lot of nasty noise from what I've read.
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Old 10th December 2010, 08:05 PM   #5
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Quote:
Originally Posted by Ted205 View Post
Hi guys

Does anyone know if the lm3886 SPiKe™ protection causes a buzzing/fuzzing sound when engaged.

I'm getting this aswell as increased heat from the chip but i'm not sure if its spike protection of a current/grounding issue.

any opinions
It could be that your speaker cables have a high element of capacitance causing oscillations, or ringing. This will give some audible buzzing, and cause an increase in heat output from the chip.

A zobel network will protect the chip against this kind of problem, and in my opinion has no audible impact on the sound of the amp. I use values of 10R and 0.1uF in parallel with the load (speaker) in my LM3875 Gainclone.

Regards,

Chris.
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Old 11th December 2010, 10:49 AM   #6
Ted205 is offline Ted205  United Kingdom
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Thanks for the replies guys.

I'm not running zobel networks (on my future mod list ) but i can change out the speaker cables as a quick check.

Also i am able to manipulate the buzz with the volumn control (lightspeed attenuator)
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Old 12th December 2010, 04:06 PM   #7
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Quote:
Originally Posted by Ted205 View Post
Does anyone know if the lm3886 SPiKe™ protection causes a buzzing/fuzzing sound when engaged.
Yes, it does.
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