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Old 24th June 2008, 02:18 PM   #1
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Default Do you hear “pop” when you turn off your amp?

I now have 2 TubelabSE amps (1 stereo & 1 mono) and stereo one turns off quietly but the monoblock makes a loud “pop” from the speaker when I turn it off. Last night as an experiment, I unplugged IC cable from the monoblock before turning it off and guess what, no “pop” at all. I use Rane AC-22 active crossover to feed these amps and was wondering if it has something to do with input signal or grounding. Is anyone familiar with this noise when turning off an amp? Thanks.
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Old 24th June 2008, 05:51 PM   #2
Jeb-D. is offline Jeb-D.  United States
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Yes, some amps I've had do that. There are to things you can do to get rid of it.

You can place a small value capacitor across the switch terminals
or
Put a metal oxide varistor (MOV) in parallel with the primary side of the transformer but after the switch.

Edit:

Sorry, I didn't read your entire post saying how it doesn't happen with the interconnect disconnected. The fixes I mentioned above are for power supply transients caused by the switch. They may not be helpful for your circumstance.
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Old 24th June 2008, 06:09 PM   #3
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IC = interconnect?

There should be a soft start circuit which should perform fast stop function to protect speakers in the event of brown outs.

Can you measure any DC offset on the IC cable that could cause the pop?

Does the stereo amp pop when you connect it to the mono IC cable (alleged cause of pop)

Does the mono amp not pop when connected to the stereo amp source.

These annoying little things can be a PITA to debug. Good luck!
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Old 25th June 2008, 01:29 AM   #4
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Are you turning the amplifiers off first followed by the other equipment or are you powering everything off at once?
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Old 25th June 2008, 02:17 AM   #5
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Quote:
Originally posted by Iain McNeill
IC = interconnect?

Can you measure any DC offset on the IC cable that could cause the pop?
Yes, IC = interconnect.

DC offset on the IC cable? You mean, put multimeter lead across "hot" and ground contact of RCA plug?

Quote:
Does the mono amp not pop when connected to the stereo amp source.
I just tried it and it does not "pop" when one of stereo IC is connected to mono amp.


Quote:
Originally posted by burnedfingers
Are you turning the amplifiers off first followed by the other equipment or are you powering everything off at once?
Amp is off first, then active x-over and everything else in reverse sequence of turning on.
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Old 25th June 2008, 03:48 AM   #6
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certainly looks like an input related issue.
DC offset may only me a few mV so you need to convince yourself what you're seeing is real. reverse test probes for identical -ve result, both leads on +ve test point etc should be 0mV etc.etc.

Measure unplugged and in-circuit for both mono amp and stereo amp source. That data set should reveal something.

What other factor could affect the power down of the amp? It's all about dumping the charge in the PSU caps, right? When the mains supply stops, the feedback loop fails and one polarity of the output will turn full on and collapse that rail.

I like the hard-stop circuit, as long as the PSU caps hold up for the relay turn off time, you never get pops.
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Old 25th June 2008, 06:58 AM   #7
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My "wintersweet highvividity" amplifier makes a pop when I turn it off. Of course there is the trick of turning down the volume before turning it off.
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Old 25th June 2008, 03:22 PM   #8
Decker is offline Decker  United States
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Old 25th June 2008, 04:01 PM   #9
kevinkr is offline kevinkr  United States
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First it is not a particularly good idea in a tube amplifier to disconnect the load to avoid a turn off pop, that little transient with load connected could turn into a bigger transient with no load, and under extreme circumstances result in large voltages across the primary of the OPT.. Relay not recommended..

Secondly it is not unlikely that the power switch is the culprit, your pop could be emi from the arc across the switch coupling into the input of your amplifier via the IC.. As previously recommended try a cap across the switch. A HV ceramic in the range of 0.01uF/1KV or similar line rated X or Y cap may do the trick.
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Old 25th June 2008, 05:17 PM   #10
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the relays are usually NC/NO changeover so you can switch from speaker load to resistor load if you want to.

He said the pop went away when connected to the stereo source.
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