When volume increased, crak-crak-crak - diyAudio
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Old 30th May 2004, 05:55 AM   #1
lukio is offline lukio  Indonesia
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Default When volume increased, crak-crak-crak

Hi Every body..
Please help

I've built an amp,,, the topologi is folded cescode with local feedback, the sound is very good...everything is normal when the volume is low.. but if the volume is increased my speaker produce sound like broken glass...crak...crak...crak and my amp limiter instantanly shutdown the amp.
But if I connect the input just one channel, not both..L or R not L and R everything goes normal. I guess it caused by bad grounding but actually I still don't know
Please help....

sorry for my english, I'm not use it everyday here


thanks for advises

cheers.

Lukio
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Old 30th May 2004, 06:56 AM   #2
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Sounds like DC voltage across the volume pot - this will produce a lot of noise. Ensure the pot does not have any DC current flowing through it (ie. use blocking capacitors).

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Old 30th May 2004, 12:25 PM   #3
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lukio,

Could you please post the schema, its difficult without it to help you.

Regards.

Alain.
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Old 30th May 2004, 02:32 PM   #4
lukio is offline lukio  Indonesia
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Default Thanks

To Centauri,
Thank alot for your advise..
I will try it soon....


cheers,,

Lukio
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Old 30th May 2004, 02:46 PM   #5
lukio is offline lukio  Indonesia
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Default Schematic

Hi Alain Dupont

I will send you the schematic and the wiring diagram too, hope you can find the problems..

thanks alot for your attention..

cheers,

Lukio
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Old 30th May 2004, 06:11 PM   #6
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It's unlikely that a noisy pot will cause your amplifier to shut down nor would it care whether the signal is fed to both or either inputs.

A schematic or layout plan might be useful in identifying the cause of this unusual problem.
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Old 30th May 2004, 06:36 PM   #7
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Hi Lukio and welcome to diyAudio

Please can you not post identical questions in several threads at the same time. I have merged your two threads together.

Thanks
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Old 31st May 2004, 02:13 AM   #8
fab is offline fab  Canada
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Hi lukio

My first very quick look at your schematics tells me that the 5.6V of the zener voltage protection circuit at base of Q16 and Q17 is too low. Remember that the mosfet IRF540 and IRF9540 have gate turn off voltage (VGFS off) in the range of 2 to 4 volts. Thus,
VZ + V1n4148- Qvbe is about Vz = 5.6 V. The gate voltage of M1 and M2 at high power level can be higher than 5.6V and anyway, the zener diode starts to conduct before its threshold voltage (leakage current). Since the IRF540/9540 can handle 20V max, I would use at least 10V and maybe 15V as Zener diodes (1N4744).

The output protecton circuit may be also to check but it is hard to see since my quicktime viewer shows not your diagram very clearly.

Good luck

Fab
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Old 31st May 2004, 05:01 AM   #9
lukio is offline lukio  Indonesia
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Default Sorry for send to multiple thread

Hi Pinkmouse..

Sorry if I send my question at different thread, i made mistaken select the forum while I submit the question..

cheers..

lukio
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