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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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Elrick
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    Probable ground problem

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    • Post n°1

    Probable ground problem Empty Probable ground problem

    Post by oldvstar Sun Jan 11, 2015 12:09 am

    Last summer I built a Bottlehead Quickie to use with my freshly built VTA ST-70. The music sounds fantastic but I have been hearing a low level hum in the background. Today I decided to track down the source of that hum. Here's my system: VTA ST-70 amp, Quickie pre-amp, Lesbox modded Yaqin MS23b phono pre-amp, and  Music Hall MMF 2.2 turntable.
    I started out by disconnecting the Quickie from the ST70. With it disconnected the only noise I hear is from the transformers. I re-connected the Quickie and the hum returns at the level I normally hear when playing an album. I then dis-connected the MS23B from the quickie so that there is nothing connected to to the inputs, with the selector switch in the off position there is hum, and with it turned to select either of the input positions the hum became very loud. It has been suggested that I install a 3 prong electrical cord on my ST-70 but I seem to remember that Bob doesn't think that's a good idea. Any suggestions for solving this issue?
    Thanks.
    Terry
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    • Post n°2

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    Post by Elrick Sun Jan 11, 2015 12:47 am

    I doubt a three prong connector would help. You could try connecting a chassis ground between the ST70 and the pre amp and or the phono, but I doubt that would help.  Can you reverse the polarity of the preamp or the phono power plugs? In other words, try plugging them in rotated 180 degrees and listen for hum?
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    Zimmer64
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    • Post n°3

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    Post by Zimmer64 Sun Jan 11, 2015 2:34 am

    I have a Quickie and the VTA ST-70 as well and had the same problem. Try to connect a cable between the ground bus of the Quickie and the chassis of either your sources or the ST70. You got to try it out, which one is the cause of the ground loop. This procedure was suggested to me on the Bottlehead forum and it worked. In my case it was the source. My long term solution was to upgrade the Quickie to a VTA SP14 preamp in my main system :-). It sounds so much better and does not have microphonics.

    Best of luck and please report back.

    Michael
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    Bob Latino
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    • Post n°4

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    Post by Bob Latino Sun Jan 11, 2015 9:33 am

    oldvstar wrote:Last summer I built a Bottlehead Quickie to use with my freshly built VTA ST-70. The music sounds fantastic but I have been hearing a low level hum in the background. Today I decided to track down the source of that hum. Here's my system: VTA ST-70 amp, Quickie pre-amp, Lesbox modded Yaqin MS23b phono pre-amp, and  Music Hall MMF 2.2 turntable.
    I started out by disconnecting the Quickie from the ST70. With it disconnected the only noise I hear is from the transformers. I re-connected the Quickie and the hum returns at the level I normally hear when playing an album. I then dis-connected the MS23B from the quickie so that there is nothing connected to to the inputs, with the selector switch in the off position there is hum, and with it turned to select either of the input positions the hum became very loud. It has been suggested that I install a 3 prong electrical cord on my ST-70 but I seem to remember that Bob doesn't think that's a good idea. Any suggestions for solving this issue?
    Thanks.
    Terry

    Hi Terry,

    You should consider adding the VTA stepped attenuator to your VTA ST-70 amp. That way you could eliminate the Quickie from your music chain. You just run the turntable directly to the Yaquin phono preamp to the ST-70 and then use the stepped attenuator on the ST-70 to control volume ..

    Bob


    Last edited by Bob Latino on Sun Jan 11, 2015 8:59 pm; edited 1 time in total
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    • Post n°5

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    Post by oldvstar Sun Jan 11, 2015 5:06 pm

    Thanks for the replies. After doing the different things suggested on this forum and the Bottlehead Quickie forum I determined that the problem is the tubes I'm using in the quickie. I found that if I'm even within 3 feet of them the hum gets louder. My intention is to build one of Roy's pre-amps but I need to keep the quickie running for awhile, maybe I can convince my wife it will make a great birthday present. ;-) She did buy me the VTA ST-70 kit for Christmas last year!
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    • Post n°6

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    Post by Guest Sun Jan 11, 2015 5:13 pm

    oldvstar wrote:Thanks for the replies. After doing the different things suggested on this forum and the Bottlehead Quickie forum I determined that the problem is the tubes I'm using in the quickie. I found that if I'm even within 3 feet of them the hum gets louder. My intention is to build one of Roy's pre-amps but I need to keep the quickie running for awhile, maybe I can convince my wife it will make a great birthday present.  ;-)   She did buy me the VTA ST-70 kit for Christmas last year!

    I have not come across a situation where getting close to a tube increases hum! I have however experienced that when getting closer to a circuit which is not properly grounded that hum will increase, this circuit can of course have tubes, but like I said, I've not come across that the tubes themselves increase in hum when getting close to them, I would keep checking!
    Of course when I say getting close to a circuit, I mean REALLY close!
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    Post by oldvstar Sun Jan 11, 2015 5:31 pm

    I can move my hands around the tubes and change the intensity of the hum, very strange.
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    • Post n°8

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    Post by Guest Sun Jan 11, 2015 5:33 pm

    oldvstar wrote:I can move my hands around the tubes and change the intensity of the hum, very strange.

    I think it is more the surrounding circuit/s being affected by your moving hands than the tubes.....
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    Post by oldvstar Sun Jan 11, 2015 6:37 pm

    Feedback I'm getting from the other forum seems to agree with you. And the search goes on.
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    • Post n°10

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    Post by Guest Sun Jan 11, 2015 7:50 pm

    does your Bottle Head Quickie have a printed circuit bard inside, or is just all point to point...also, the top panel, is it metal or acrylic?
    I am assuming the chassis is wooden and there is no bottom plate?
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    • Post n°11

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    Post by oldvstar Sun Jan 11, 2015 8:55 pm

    My Quickie has point to point wiring, acrylic top plate, wood chassis, and no bottom plate
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    • Post n°12

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    Post by Guest Sun Jan 11, 2015 9:08 pm

    oldvstar wrote:My Quickie has point to point wiring, acrylic top plate, wood chassis, and no bottom plate

    have you had that hum issue since you built the Quickie, or is it something that started a while ago, I also assume it is battery powered?
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    • Post n°13

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    Post by oldvstar Mon Jan 12, 2015 12:28 am

    The hum has been there from the beginning, and it is battery powered.
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    • Post n°14

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    Post by Guest Mon Jan 12, 2015 1:10 am

    oldvstar wrote:The hum has been there from the beginning, and it is battery powered.

    interesting. The supply being all DC, ie battery, I would not have expected a hum issue. The only thing I can think of is some kind of 'ground loop' caused from the external input and output source's ground.
    What I would try, is to isolate the input RCA's ground from the batteries -ve. Then connect the ground from those input RCA's to your input source's ground....I think....maybe other's could chime in here....Roy or Troy, what do you guys think?....would this idea cause some different issues??....maybe I am barking up the wrong tree??
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    • Post n°15

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    Post by oldvstar Tue Jan 20, 2015 10:39 pm

    I want to follow up and thank all of you who responded to my plea, everything is now nice and quiet. I ended up doing multiple things; I found a loose nut on an RCA connector, tightening it quieted things down quite a bit. I also ran a ground wire between the Quickie and the phono-preamp, and replaced my RCA 3S4's with a pair of Telefunken DL92's. The only sound I hear now is the low hum of the ST70's transformers.
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    • Post n°16

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    Post by corndog71 Wed Jan 21, 2015 1:24 pm

    Well done!  The Quickie is a great little preamp and tough to beat for the money.  It also can be improved with cap changes and better vibration control.

    I created a crazy over-built 2-chassis version which worked well until I got the Bottlehead Smash preamp.

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    • Post n°17

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    Post by arledgsc Thu Jan 22, 2015 11:37 am

    That is interesting and glad you found the source of your problem.... How long do those batteries last in normal operation?
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