Pop on amp shutdown

[Brent]

Hi,

I am having an issue with a pop of varying intensity--from annoying to alarming--when I turn off an amp connected to my Smash with SmashUp. Correct shut down sequence is being followed (amp, then preamp).  My first thought is that it was something with one or both of my Paramounts, which it still could be, maybe. Thing is, I get the same pop with my SEX 2.0 downstream of the Smash, and I don't get the power down pop on either amp when a Submissive is in the chain in place of the Smash. Hence my suspicion that it is the Smash.

I redid the voltage check from the SmashUp manual. They are spot on on the right channel and just off for the left.  Here are the distinctions:

1. All the voltages that should be 150 +/- 1% are 149.9 for the right channel and 147 for the left. So 2 % off instead of within 1%.
2. All the voltages specified as 3 to 5V are 4.16 in the right channel and 4.56 in the left. So, within spec but not matched.

My question then, are these differences enough to cause a pop on shut down of the power amp while the preamp is still on?  & if so, how do I correct it?  I tried a different 4p1l in the off channel and got identical voltages.  I only have the 6sn7 that shipped with the SmashUp, so I haven't swapped that one out.  if the voltage discrepancy isn't such that it would cause this behavior, where should I look next?  I can look at amps too, but the fact that it happens with two different amps made me investigate the Smash first.

Thanks,
Brent

[Paul Birkeland]

How long are you waiting between turning off amp and preamp?

Are the amplifiers and preamp plugged into the same outlet?

Does the behavior change with the submissive if you ground its chassis to the Paramount chassis?

-PB

[Brent]

It pops on turnoff of the power amp, even if I don't turn off the pre at all.

No difference whether the Submissive is grounded to one, both, or neither Paramount chassis. Thank you for suggesting that. I should have tried it already, since the grounding is an obvious difference between the pre and the passive.  I also tried turning off both Paramounts attached to nothing except the wall with no or minimal pop, just as a control.

Any ideas why the upstream components would affect power off behavior of the amp? There was another thread with a similarly problem that ended without resolution (OP seems to have abandoned it). Hopefully we can figure this one out.

Thank you for your help.

Brent

[Brent]

I continue to work on this.  Grounding my Seduction chassis plate to the Smash chassis plate appears to reduce the pop to a negligible tick that I wouldn't think twice about, equivalent to what I get with the Submissive in the chain. It will take time to make sure that has solved the problem, though, since there is some variation in intensity maybe depending on how long the system has been on. 

Either way, it appears to be a system grounding issue.  Any other suggestions or devices that could help with that generally?  I also have a TV and Blu ray player in the mix, which I prefer to leave there.  The BH pieces (seduction, smash, fix, paramounts) are all otherwise operationally sound and have been for a few months to several years. Everything is plugged into an unswitched Wiremold strip. As long as this symptom doesn't raise any flags for something serious, I will just continue to experiment with different configurations of connected devices and grounding schemes until I am happy with it.

[Paul Birkeland]

Check the DC resistance between terminal 6 in the Smash and the #8 grounding screw at the IEC power entry module.  Do the same check in the Seduction, but from the shell of an output RCA jack to the grounding screw.  Next, plug the Seduction and Smash into your power strip, then unplug the power strip from the wall.  With no interconnects connecting the Smash and Reduction, what DC resistance do you get between chassis plates?

The plates should already be well connected through the power cords and power strip that you have.  There isn't a big issue with manually connecting the plates, but there may be some external influence that can be removed so that you don't have to.

-PB

[Brent]

Smash terminal 6 to IEC ground lug: 0.1-0.2 ohm
Seduction IEC ground lug to output RCA shell:  0.1 ohm
chassis to chassis plugged in to unplugged strip: 0.4-0.5 ohm

I'm not sure how much the chassis to chassis ground is helping--I still got a fair, if not scary, pop at least once with that arrangement too.

[Paul Joppa]

Often a system with TV cable will have a ground that is not close to the power line safety ground. You can temporarily disconnect the cable and see if that has an effect - if it does, cable isolators are readily available.

Just a thought.

[Brent]

Paul J, Thanks for the suggestion.  I only have the antenna in my attic for broadcast programming.  Still, it was there when I bought the house & I don't know how or if it's grounded.  No change though if I disconnect it.

As another data point, I am using my SEX 2.0 as a preamp this morning with a TRS to stereo RCA adapter, and there is only a little 'tick' on shutting down the Paramounts.  This I would consider normal.  SEX has MQ iron & C4S upgrade.

Thanks everyone for your help with this, by the way. I have other options, but I would like to be able to use the Smash without this happening. I wouldn't have been using the Smash if resistances hadn't been on after I built it, but I can do those if it would help. Can't remember if I've tried only the smash and Paramounts with no source or anything else plugged in to the amps or the wall/strip, but I will try that too.  Any other suggestions?

[fullheadofnothing]

Have you tried this with no inputs connected to the Smash?

[Brent]

I have. It still pops fairly loudly when I turn off the Paramounts only when only the Smash and nothing else is connected.

[Paul Joppa]

Finally penetrated my skull that this happens immediately when the Paramount switch is thrown - right? So it's probably the RF energy generated by the minute spark in the switch, being picked up by the Smash.

An RC snubber across the Paramount power switch would reduce the spark - 10 ohms series with 0.1uF are typical values. Or something in the Smash to reduce its RF sensitivity - not sure what that might be. Or separate the two components by a greater distance. Or just ignore it; it's not causing any harm.

My two cents.

[Grainger49]

If you don't have a 10 Ohm resistor try a 0.1uF 1kV or 0.01uF 1kV alone across the Paramount switches.

[Chris65]

Yes, a small value cap across the switch will work just make sure it is X2 (across line voltage) rated or better.

[Brent]

Yes, Paul, that's it. It just seems much louder than it should be. I will give the RC snubber a shot and report back to confirm that it works.  I wasn't sure about harm, but I didn't like sending loud, non-signal transients through my speakers.  It's good to know that there is  no harm though.

Thanks, everyone, for your help.

Brent

[Brent]

If I put a cap & resistor across the switch, will there always be current draw then? & if so, will it not make it past the RC snubber?

I haven't done this yet and was just wondering.  I am in less of a hurry since it is not a symptom of an actual problem somewhere.