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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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Zimmer64
guentherj2
6 posters

    VTA SP12 Popping Noise

    guentherj2
    guentherj2


    Posts : 50
    Join date : 2013-06-22
    Location : Bellingham, WA

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    Post by guentherj2 Sun Sep 29, 2013 11:13 am

    Greetings All:

    My standard operating practice is to have my volume control set at low before changing/selecting different sources. However, when I forget to turn the volume down or have the volume at a mid-level setting and move the source selector to Phono from a different source I hear a loud POP. This only happens the first time I select phono. If after the first POP I move the source selector to a different source and then back to Phono it doesn't happen - just the first time.

    Is this normal or indicative of a problem?

    Also - when the SP12 source selector is on Tuner, I get a some noise at every volume volume notch when changing the volume control.

    Maybe this is normal and I just need to be dilligent about keeping my volume down when changing the source selector control?

    Any similar experiences or thoughts?

    Thanks,

    John
    Zimmer64
    Zimmer64


    Posts : 123
    Join date : 2013-01-29
    Age : 60
    Location : Switzerland

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    Post by Zimmer64 Sun Sep 29, 2013 1:22 pm

    I have the same symptoms with my SP 14 and my CD player. It even affects my volume control. The pop of the source selector happens only once The pops of the stepped attenuator goes away after playing some music. How strange is that?.... My guess is that it is static or some grounding issue, but I could not figure it out.
    arledgsc
    arledgsc


    Posts : 494
    Join date : 2012-11-30
    Age : 70
    Location : Santa Rosa CA

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    Post by arledgsc Sun Sep 29, 2013 2:29 pm

    Slight DC shifts in potential could be heard as a pop as the various inputs are connected and disconnected with the switch.  This can be heightened with capacitive coupling of the stages since the caps can store a charge.  And since the phono stage has more gain then it may just simply amplify the "pop" more.  But should be of no concern except for the annoying noise - if not loud enough to damage you speakers.
    deepee99
    deepee99


    Posts : 2244
    Join date : 2012-05-23
    Location : Wallace, Idaho

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    Post by deepee99 Thu Oct 24, 2013 5:38 pm

    Sounds like one or more of your tubes in the line preamp is microphonic. That will produce exactly the symptoms you describe; I had some noisy 6CG7s in my SP-13 that did this.
    kevco
    kevco


    Posts : 69
    Join date : 2009-07-16
    Location : Aldan, PA, USA

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    Post by kevco Mon Oct 28, 2013 11:06 am

    My Sp-12 has recently developed some popping noises while turning the stepped volume attenuator up or down especially in the low volume range. I have experienced some pinging noises in the past while moving the attenuator due to microphonic line stage tubes. This however is constant no matter what tubes are installed. I'm wondering if the attenuator needs to be or even can be cleaned...Anybody have knowledge on this? I've got Deoxit and Dustoff. I'm kind of embarrassed to mention that due to space limitations in my home, my cat's litter box is within the same open plan area as my system and the dust produced by adding new clumping litter to the box tends to float throughout the area and must be constantly removed from surfaces. This is fine clay dust, invasive stuff.
    deepee99
    deepee99


    Posts : 2244
    Join date : 2012-05-23
    Location : Wallace, Idaho

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    Post by deepee99 Mon Oct 28, 2013 11:22 am

    kevco wrote:My Sp-12 has recently developed some popping noises while turning the stepped volume attenuator up or down especially in the low volume range.  I have experienced some pinging noises in the past while moving the attenuator due to microphonic line stage tubes.  This however is constant no matter what tubes are installed.  I'm wondering if the attenuator needs to be or even can be cleaned...Anybody have knowledge on this?  I've got Deoxit and Dustoff.  I'm kind of embarrassed to mention that due to space limitations in my home, my cat's litter box is within the same open plan area as my system and the dust produced by adding new clumping litter to the box tends to float throughout the area and must be constantly removed from surfaces.  This is fine clay dust, invasive stuff.
    We just take the cat-box outside to fill it, let the dust-storm settle for a couple of minutes, then bring it back inside. QED
    avatar
    Jim McShane


    Posts : 237
    Join date : 2011-10-19
    Location : South Suburban Chicago

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    Post by Jim McShane Mon Oct 28, 2013 11:48 am

    arledgsc is right on the money, a shift in DC level is almost always the cause. Often when you change selector switch positions you often connect to circuitry with either charged up caps that discharge and cause the noise or vice-versa. From a design point of view often you'll see very high value resistors used to keep the cap charged or to keep it discharged when not in the active circuitry.

    It's always a good idea to have clean contacts, good tubes with good contact in the socket, etc. but those are not often the cause of the pop. As arledgsc said as well - if it isn't too loud to damage something don't worry about it.

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