VTA ST70 static pop on shutdown

I started using my vta st70 with an active preamp. (before I was just using a volume pot with no issue). I turn down the volume on the pre and then I turn off the power amp first and I get a quick static/arc pop when I toggle the switch. Its intermittent, it doesn't occur each time but it does the majority of the time.

I assume the switch is good since it never occurs when I have it plugged into the volume pot instead. I like to avoid having to replace the switch or add a cap across the switch unless you recommend that.


Is this damaging to the speakers or amp?
Do you think I should try powering down the preamp first? Or will this give me an even bigger surprise?

The reason for the pop is that the breaker breaks at randomly parts of the AC waveform.
This may be reduced by connecting a cap and resistor in parallell with the breaker, note that
this should be a mains-certified ( whatever that means in US ) component.

I avoid this by using a SSR to power my poweramps, they close and opens at the zero crossing

Is this damaging to the speakers or amp?

Probably unless the pop is not *very* loud indeed.

Do you think I should try powering down the preamp first? Or will this give me an even bigger surprise?

Bigger surprise, most likely. Amp on last, off first is generally the ideal.

Try this: With the amp turned off, install shorting plugs on the amp input. Turn it on. Turn the VC(on the amp, if so-equipped) to *Full*. Assuming no objectionable noises, allow the amp to run for about five full minutes. Turn off. Do you get the same *POP*? If so, there is an issue with the amp. If not, with the pre-amp.  Let us know.

How about just simply switching everything off at once from the power strip? Do you think I will get the "snap" then? If I try this, will I get the same surprise I would if I switched the preamp off first?

also

If I add a cap (and maybe a more robust toggle switch).... what value do I use? And is that simply added across the switch terminals?

This has occurred with 2 different active preamps but not with a passive preamp so its hard to point a finger at either.

OK so I notice

Turning off the pre first it doesn't pop immediately, but it does a few moments after switching it off as the tubes come down.

However, turning off both the pre and amp at the same time via the power strip, there is no noise at all.

Is there any harm in turning off the equipment at the power strip each time?

Is there any harm in turning off the equipment at the power strip each time? [/quote]

Nope.

rymi wrote:OK so I notice

Turning off the pre first it doesn't pop immediately, but it does a few moments after switching it off as the tubes come down.

However, turning off both the pre and amp at the same time via the power strip, there is no noise at all.

Is there any harm in turning off the equipment at the power strip each time?

No. It's in addition convenient.

Great, works for now but just masking an issue....

so as far as adding a snubber cap.

What value? A resistor too? Both across the switch?

rymi wrote:Great, works for now but just masking an issue....

so as far as adding a snubber cap.

What value? A resistor too? Both across the switch?

Type X if across the mains.
Type Y if from Mains to Chassis
Some caps are rated both ways.

Value = 0.10 uF in most cases under discussion here.

If the amp does not *POP* on its own - then there is no need for this cap. Full Stop.

I didn't try shorting rca's. However, it doesn't do it with the simple volume pot instead of the active preamp. So does that means the same thing.... the snubber cap is not necessary?