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Old 6th October 2013, 02:11 AM   #1
nhuwar is offline nhuwar  United States
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Default Thump sound at turn off of a power amp

Hey guys,

I've been hunting for this but I've came up dry. I just got an ppp 6550 amp. Its a audio research d115. When I turn it off I get a click then a loud thump out of the speakers. What is the usual cause for this? I'm guessing its carted by a cap discharging but I'm not sure where to begin to find it. Its a loud enough thump to get me worried about my GPA 416's its driving.


Any help would be great.

Thanks,
Nick
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Old 6th October 2013, 02:53 AM   #2
DUG is offline DUG  Canada
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Is it louder than the music you usually play?
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Old 6th October 2013, 03:06 AM   #3
nhuwar is offline nhuwar  United States
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Well that depends on my mood, lol. But for the most part yes it is. I'd say its close to 100db if not just over it.

But its not consistent. Sometimes its not as loud.

Nick
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Old 6th October 2013, 03:22 AM   #4
ChrisA is offline ChrisA  United States
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Originally Posted by nhuwar View Post
Hey guys,

I've been hunting for this but I've came up dry. I just got an ppp 6550 amp. Its a audio research d115. When I turn it off I get a click then a loud thump out of the speakers. What is the usual cause for this? I'm guessing its carted by a cap discharging but I'm not sure where to begin to find it. Its a loud enough thump to get me worried about my GPA 416's its driving.


Any help would be great.

Thanks,
Nick
I bet the B+ voltage goes down to near zero way-fast. Add a bigger filter cap and see what happens. Inthe best case you should turn off the power and the amp continues to make music for a second or so then fades out. For that level of performance you might need another RC stage prior to where the power goes into the output transformer's center tap. But try an experiment with a bigerr cap rigged in parallel using wire with clips.
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Old 6th October 2013, 03:38 AM   #5
nhuwar is offline nhuwar  United States
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its got 4 800 mfd caps on the b+ supply so I am doubting it. But I'll test them to make sure there good. I've also got a few clarity tc caps and jj 500 vdc caps I can test with.

I've never put a meter on it either which I probably should.
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Old 6th October 2013, 03:54 AM   #6
ChrisA is offline ChrisA  United States
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OK, already have high filter caps value. I wonder if the ground reference chances when you turn off the power.

How long does the music continue after power off? At least long enough to hear the "thump"
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Old 6th October 2013, 03:56 AM   #7
nhuwar is offline nhuwar  United States
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That one I'll have to check out and report back in the morning.

Thanks,
Nick
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Old 6th October 2013, 04:07 AM   #8
AJT is offline AJT  Philippines
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turning the volume to zero before hitting the off switch still produces thumps....?
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Old 6th October 2013, 04:11 AM   #9
nhuwar is offline nhuwar  United States
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Yep.
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Old 6th October 2013, 06:19 AM   #10
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Quote:
Originally Posted by nhuwar View Post
Hey guys,

I've been hunting for this but I've came up dry. I just got an ppp 6550 amp. Its a audio research d115. When I turn it off I get a click then a loud thump out of the speakers. What is the usual cause for this? I'm guessing its carted by a cap discharging but I'm not sure where to begin to find it. Its a loud enough thump to get me worried about my GPA 416's its driving.


Any help would be great.

Thanks,
Nick
its normal.
its called counter emf of the output transformer.


get a 5A dpdt relay and switch the speaker in and out.
I used 115V aircraft ones ( cheap and lower dropout) and connected it to the violet wire off the power transformer primary (100V tap).
I took a 100 ohm 12W resistor and went across the nc circuit to speaker common so when the relay is de-energized, the transformer had a load. when the relay closes, it switches to the speakers.
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