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Old 26th February 2004, 06:52 PM   #1
Derrick is offline Derrick  United States
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Default Question about popping Noise

I recently acquired a used Audio Valve Assistent 20 Integrated Tube amp with 2 set of brand new RCA tubes. The amp seem to work properly. But every time I power off the amp, it made a popping noise. It's not real loud, but it does pop.

Base on my limited experience with tube amp, I thought this probably caused by a bad tube so I swapped all the tubes out with the second set of tubes. Now, the popping noise went away and reinstate with a little thump noise via the speakers (sort of a small puff of air pressure that push the speaker drivers outward.

Any thoughts or suggestions on what would cause this?

Thanks in advance,
Derrick
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Old 27th February 2004, 01:18 AM   #2
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Hi,

Does this popping occur with the preamp muted or the volume knob turned down all the way?

The recommended turn-of sequence for tube gear is:

- mute preamp.

- turn of amp(s).

- turn of preamp with mute engaged.

- turn of source(s).

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Old 27th February 2004, 05:31 AM   #3
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I turn off my amps at night all on the same power strip. Works fine. Rarely any popping whatsoever. In any case, the chances are, the power switch isn't adequately bypassed and is causing an HF spike when you open it. This induces voltages in nearby signal wires causing a noise. If it isn't speaker-killing, don't worry about it.

Turning off the preamp first won't do anything. It's in the power amp. Unless you suspect muting the preamp grounds the output, which might have a marginal effect.

Tim
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Old 27th February 2004, 09:58 PM   #4
Derrick is offline Derrick  United States
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Quote:
Does this popping occur with the preamp muted or the volume knob turned down all the way?
Yes, it still pop with volume down all the way. BTW, this is an integrated tube amp and there is no mute button.
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Old 27th February 2004, 10:18 PM   #5
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Hi,

Quote:
Yes, it still pop with volume down all the way. BTW, this is an integrated tube amp and there is no mute button.
As Tim suggests it may be the power switch causing a spark when switched.

To find out just pull out the powercord as a means of powering of.
If that doesn't cause the noise a .047F 250VAC snubber cap across the poles of the switch should cure it.

Cheers,
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Old 27th February 2004, 10:34 PM   #6
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The popping might come from the HT caps still carrying tension after the fillament supply is shut down, two ways to go: dont care, not harmfull. (affecting tube life a little but a i suppose this is an EL84 amp and theese tubes live forever, allmost) If to anoying, install bleeder resistors on the HT caps ( if its a multisection cap replace with single caps)
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