audible pop when turning power off on preamp

[hasafraker]

I have a Decware zsp1 preamp that I've had for a number of years now, it's always made a small pop when I turn the power off but the other day it was quite loud. Since then the little pop when I turn the power off is back to it's little pop self but it occurred to me that it probably shouldn't pop at all so...

thoughts as to why this may be happening? I realize this isn't the Decware forum but the last time I visited it recently, several of the support threads that I asked questions in or posted comments to... haven't been touched in over a year. I also think they stopped selling kits so most of the folks who support kit builders there have moved on. I still have Steve's email address i think so I may email him but thought I would bounce this off you good and knowledgeable folks.

I have the original pdf with the schematic for anyone who cares to check it out. There are also a few photos of the layout and my preamp is very very close to the original layout. https://dl.dropboxusercontent.com/u/231135838/ZSP-1.pdf

[Paul Birkeland]

Is this a pop that comes through your speakers (which can be remedied by just turning your amp(s) off first), or you can hear the preamp itself popping?

[Doc B.]

I don't really feel comfortable with this. If Decware were out of business I would have no problem with offering some suggestions. But if they are just not supporting their product we tread a fine line of messing with someone else by offering to do said tech support. PB has offered the suggestion of powering amps off first, and I think we will leave it at that.

[hasafraker]

Doc,

sorry if you felt I was putting you in a funny spot, I didn't pose the Q to "Bottlehead" but to the DIY community here. I will take the Q to the Decware forum and pray there is someone still lurking with any idea.

[Grainger49]

Many tubed devices leak a little bit of DC as they turn on.  This has been known for 80 years.  But it is usually a small voltage and is harmless. 

My Ack!dAck! is capacitor coupled and it says, "thump" if I turn it off before shutting down the rest of the system.  I did that yesterday.  I just forgot.

You are not alone.  We have been suggesting to turn on your system from source to amp with a few seconds pause to allow the bleed through to pass.  And you turn off the system from amp to source with the same pause. 

My worry is that it increased in volume and severity.  Unless you have recently inserted a new component in the chain I would point the accusing finger at the preamp.  I would contact Decware.  Possibly the output cap is giving up the ghost.  But surely they can shed some knowledgeable light on the problem.

[hasafraker]

Thanks Grainger, I did post to the decware support forum, the first new thread for that preamp in over a year, I am not hopeful. I did add a new component just last weekend, but the little pop was there before adding the new phono stage, it did it before with the old one too. I will just keep an eye on it. If the pop worsens I will take it down to the bench and investigate. I still have the documentation, emails, and schematic. It's been a very solid preamp.

[RPMac]

I use my FP III as volume comtrol ahead of the Stereomour with its volume set "full up".
The loudness of the pop varies with the volume of the FP III.
Should I turn the volume of the FP III down before shut down or is this something I should worry about?

[Grainger49]

Robert,

The volume control on the FP III is at the inputs.  The pop is generated by the output cap leaking a little DC.  It is best to follow the turn on turn off procedure in FAQ #1.

[RPMac]

I follow proper on/off sequence.
The Stereomour input is a 100K pot and, at full volume, I assume it acts as a 100K grid resister.
With the 20 mu DHT driver, the FP III volume is set 30-40% higher than with my ParaBee's.
I never noticed a pop before. Just wanting to be sure there is nothing going on that I need to be concerned about.