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    The SP14, mechanical isolation and you.

    bbqjoe
    bbqjoe

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    Post by bbqjoe on Sat Jan 19, 2019 9:19 pm

    It became apparent to me today that some isolation might be necessary for this preamp.
    The cabinet I have it on is quite susceptible to vibration, especially since the speakers are right next to it.

    I went to googling for solutions, and read many.
    Using a partially deflated wheelbarrow inner tube made as much sense as about anything else I saw out there.

    But instead of placing the preamp on gold plated Rhodium ball bearings balanced on slices of the Glockman diamond, why not just decouple the board from the chassis by removing the screws and standoffs, and resting the board on a simple layer of fiberglass insulation?

    It's not like you pick up the preamp and shake it every time you turn it on, right?
    vtshopdog
    vtshopdog

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    Post by vtshopdog on Sat Jan 19, 2019 10:10 pm

    General damping and isolation can be achieved by stacking materials that resonate at different frequencies.  I use aluminum feet with rubber bottoms and a layer of cork sandwiched between the aluminum feet and chassis bottom.  For my TT I use above bolted to a wooden plinth with sorbothane domes stacked between the plinth and deck.  

    Sorbothane domes will likely do the trick for you - they are affordable and sold in various durometers so you will need to select according to your amps weight.  They will stain wood surfaces if left in direct contact for extended time periods.

    Having the board flopping about in the chassis?  Umm, I’ll leave that to others here to address.......
    bbqjoe
    bbqjoe

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    Post by bbqjoe on Sun Jan 20, 2019 2:10 am

    vtshopdog wrote:General damping and isolation can be achieved by stacking materials that resonate at different frequencies.  I use aluminum feet with rubber bottoms and a layer of cork sandwiched between the aluminum feet and chassis bottom.  For my TT I use above bolted to a wooden plinth with sorbothane domes stacked between the plinth and deck.  

    Sorbothane domes will likely do the trick for you - they are affordable and sold in various durometers so you will need to select according to your amps weight.  They will stain wood surfaces if left in direct contact for extended time periods.

    Having the board flopping about in the chassis?  Umm, I’ll leave that to others here to address.......

    Well, maybe not flopping about, but certainly not hard mounted to the chassis.
    Peter W.
    Peter W.

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    Post by Peter W. on Sun Jan 20, 2019 10:24 am

    If vibration of any nature is affecting the audio output from a preamp, something else is going on. Fix that first, before worrying about physical isolation.
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    Post by Guest on Sun Jan 20, 2019 12:15 pm

    I have never had any issues with vibration or noise pickup, irrespective if the transformer is mounted on top of the chassis or inside and I use mainly wooden chassis' for my builds. Not to mention any external vibration pickup! The only way that I can see that perhaps happening is a microphonic tube/s?
    Of course, everything needs to be bolted and screwed down really well. These days, once I re checked every screw and nut, I use nail polish and dab that on the nut or screw, to prevent it from working itself loose over time. I learned this the hard way!!
    Wiring, well, I twist EVERY AC hookup wire and keep them as far away from any DC wires or pcb's as possible. I will even make the wires a bit longer to route them properly. This extra bit of length will make no difference what so ever.
    If I cannot keep AC wiring away from DC wiring or pcb's, I elevate that AC wiring away from those other bits.
    I cannot stress neat wiring and tightened nuts & bolts enough, it makes ALL THE DIFFERENCE!
    bbqjoe
    bbqjoe

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    Join date : 2018-12-03

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    Post by bbqjoe on Sun Jan 20, 2019 12:35 pm

    erhard-audio wrote:I have never had any issues with vibration or noise pickup, irrespective if the transformer is mounted on top of the chassis or inside and I use mainly wooden chassis' for my builds. Not to mention any external vibration pickup! The only way that I can see that perhaps happening is a microphonic tube/s?
    Of course, everything needs to be bolted and screwed down really well. These days, once I re checked every screw and nut, I use nail polish and dab that on the nut or screw, to prevent it from working itself loose over time. I learned this the hard way!!
    Wiring, well, I twist EVERY AC hookup wire and keep them as far away from any DC wires or pcb's as possible. I will even make the wires a bit longer to route them properly. This extra bit of length will make no difference what so ever.
    If I cannot keep AC wiring away from DC wiring or pcb's, I elevate that AC wiring away from those other bits.
    I cannot stress neat wiring and tightened nuts & bolts enough, it makes ALL THE DIFFERENCE!

    Here's what I found.
    It happened when I set a remote on the cabinet holding the amp and preamp.
    I heard noise through the system.
    If I tap the cabinet, really lightly, I mean really lightly, I get thung boingy sound through the left speaker.

    Just to see, I switched both tubes on each channel with each other, now I get it on the right.
    It also gives a staticy sound when music is playing through the channel.

    I guess I must have a bad tube?
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    Post by Guest on Sun Jan 20, 2019 1:01 pm

    bbqjoe wrote:
    erhard-audio wrote:I have never had any issues with vibration or noise pickup, irrespective if the transformer is mounted on top of the chassis or inside and I use mainly wooden chassis' for my builds. Not to mention any external vibration pickup! The only way that I can see that perhaps happening is a microphonic tube/s?
    Of course, everything needs to be bolted and screwed down really well. These days, once I re checked every screw and nut, I use nail polish and dab that on the nut or screw, to prevent it from working itself loose over time. I learned this the hard way!!
    Wiring, well, I twist EVERY AC hookup wire and keep them as far away from any DC wires or pcb's as possible. I will even make the wires a bit longer to route them properly. This extra bit of length will make no difference what so ever.
    If I cannot keep AC wiring away from DC wiring or pcb's, I elevate that AC wiring away from those other bits.
    I cannot stress neat wiring and tightened nuts & bolts enough, it makes ALL THE DIFFERENCE!

    Here's what I found.
    It happened when I set a remote on the cabinet holding the amp and preamp.
    I heard noise through the system.
    If I tap the cabinet, really lightly, I mean really lightly, I get thung boingy sound through the left speaker.

    Just to see, I switched both tubes on each channel with each other, now I get it on the right.
    It also gives a staticy sound when music is playing through the channel.

    I guess I must have a bad tube?

    I would probably point more to a microphonic tube, definitely time to change that tube I'd say!
    bbqjoe
    bbqjoe

    Posts : 96
    Join date : 2018-12-03

    The SP14, mechanical isolation and you. Empty Re: The SP14, mechanical isolation and you.

    Post by bbqjoe on Sun Jan 20, 2019 1:03 pm

    erhard-audio wrote:
    bbqjoe wrote:
    erhard-audio wrote:I have never had any issues with vibration or noise pickup, irrespective if the transformer is mounted on top of the chassis or inside and I use mainly wooden chassis' for my builds. Not to mention any external vibration pickup! The only way that I can see that perhaps happening is a microphonic tube/s?
    Of course, everything needs to be bolted and screwed down really well. These days, once I re checked every screw and nut, I use nail polish and dab that on the nut or screw, to prevent it from working itself loose over time. I learned this the hard way!!
    Wiring, well, I twist EVERY AC hookup wire and keep them as far away from any DC wires or pcb's as possible. I will even make the wires a bit longer to route them properly. This extra bit of length will make no difference what so ever.
    If I cannot keep AC wiring away from DC wiring or pcb's, I elevate that AC wiring away from those other bits.
    I cannot stress neat wiring and tightened nuts & bolts enough, it makes ALL THE DIFFERENCE!

    Here's what I found.
    It happened when I set a remote on the cabinet holding the amp and preamp.
    I heard noise through the system.
    If I tap the cabinet, really lightly, I mean really lightly, I get thung boingy sound through the left speaker.

    Just to see, I switched both tubes on each channel with each other, now I get it on the right.
    It also gives a staticy sound when music is playing through the channel.

    I guess I must have a bad tube?

    I would probably point more to a microphonic tube, definitely time to change that tube I'd say!
    I just built the kit, the tubes came with it. I suppose a bad one out of the box is not unheard of.
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    Post by Guest on Sun Jan 20, 2019 1:09 pm

    perhaps not electrically bad, but microphonic, yes, possible for sure
    tubes4hifi
    tubes4hifi
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    Post by tubes4hifi on Sun Jan 20, 2019 2:19 pm

    Joe,
    The SP14 kit ships with iso-mounts to use between the chassis and PCB. The bottom of the chassis is lined with dampening material. Then the chassis is fitted with rubber feet.
    If that's not enough, you can replace the rubber feet with sorbothane feet or use that wheelbarrel inner tube.
    All of those things together should work much better than gold plated Rhodium ball bearings, guaranteed!
    But it does seem maybe you have a microphonic tube, which isn't that common but it does happen occasionally.
    bbqjoe
    bbqjoe

    Posts : 96
    Join date : 2018-12-03

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    Post by bbqjoe on Sun Jan 20, 2019 2:25 pm

    tubes4hifi wrote:Joe,
    The SP14 kit ships with iso-mounts to use between the chassis and PCB.  The bottom of the chassis is lined with dampening material.   Then the chassis is fitted with rubber feet.
    If that's not enough, you can replace the rubber feet with sorbothane feet or use that wheelbarrel inner tube.
    All of those things together should work much better than gold plated Rhodium ball bearings, guaranteed!
    But it does seem maybe you have a microphonic tube, which isn't that common but it does happen occasionally.

    Well at first, I hadn't considered a microphonic tube, and being a tube noob, thought this was a standard problem people have.
    But after the tube swap, apparently I was trying to solve a problem I shouldn't be having.

    So I guess a new tube is in order.

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