The Dynaco Tube Audio Forum

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


    New mk3 clone but Low humming (22mv) advice.

    Share

    GabrielG

    Posts : 11
    Join date : 2012-12-26

    New mk3 clone but Low humming (22mv) advice.

    Post by GabrielG on Sat Jan 12, 2013 9:14 pm

    I just finished one of the mk3 clone and let me say the sound is exactly like I wanted. The VTA-octal is a must have.

    Now I have unresolved grounding issues...

    Some information on my build:
    1. I didn't put the 0.002uf cap with the center tap of the heaters.
    2. I grounded the output tubes to the capacitor bank
    3. the case is wood and there is no earth attached from the power outlet to the capacitor bank ground.
    4. there is a separate transformer for the bias on the VTA octal, one side of the secondary is connected to the bias and the other to the capacitor bank ground.

    What I will do next:
    The next step was to disconnect the ground from the speaker binding post and attach it directly to the capacitor bank (-) instead of the VTA board.

    Any positive input is appreciated from people who knows tricks and amplifiers. Thanks!


    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by tubes4hifi on Sun Jan 13, 2013 4:42 pm

    add the filament winding capacitor.
    make sure ALL grounds (PCB and speaker output and power supply caps are all connected together (ground)
    try connecting ground to AC ground (3rd wire on power cord)

    GabrielG

    Posts : 11
    Join date : 2012-12-26

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by GabrielG on Sun Jan 13, 2013 6:20 pm

    ok ill do that

    GabrielG

    Posts : 11
    Join date : 2012-12-26

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by GabrielG on Tue Jan 15, 2013 10:57 pm

    1. I put the 0.002uf cap with the center tap of the heaters. = no change
    3. I attached the earth to capacitor ground = more high frequency hum, no change

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by Bob Latino on Wed Jan 16, 2013 7:42 am

    Those two caps should be .02 uF and not .002 uF. I don't know if that is the cause of the hum you have but you should use a larger cap there. That center tap of the filament heaters only looks at 1/2 the AC heater voltage (about 3 to 4 volts AC) so any 50 volt or higher cap will be fine.

    Also - make sure that the INPUT jack ground is only grounded to the driver board and is NOT star grounded to the chassis.

    Bob

    GabrielG

    Posts : 11
    Join date : 2012-12-26

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by GabrielG on Wed Jan 16, 2013 11:42 pm

    Hi Bob, thanks for taking the time to help. It means so much to me.

    The capacitor(2x parallel 0.01 100v) is 0.02 actually.

    The input is to the driver VTA board only, and the power supply ground is going with a twisted wire to the VTA with the power wire.

    All voltages are within 1 % accuracy of the requirements...

    Following-up I tried to isolate the issue by removing tubes...

    the power tubes have 0 hum , the tube driving the power tubes has 0 hum. (tubes are 100 % new and functionning properly)

    All the interference or ground loops happens only when all stages are powered up.

    Something is happening at the input tube.

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by Bob Latino on Thu Jan 17, 2013 8:55 am

    See if you can post a photo of the inside wiring here on the forum. One of us may be able to pick up on something in the wiring that could be a potential source of hum ..

    Bob

    GabrielG

    Posts : 11
    Join date : 2012-12-26

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by GabrielG on Thu Jan 17, 2013 11:35 pm




    I moved the power supply wire for the VTA down and the input wire left. The hum decreased form 22 mv to 8 mv !!!!
    Without feedback it is 13.5 mv, so feedback reduces by 5.5 mv the noise.

    I will try to move even more the wires away and rewire the input wire that seems the most sentitive to catch interference from the VTA.

    Moving the heater wires didn't change anything, everything else is dead quiet ( second tube and power tubes).


    GP49

    Posts : 718
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by GP49 on Fri Jan 18, 2013 1:42 pm

    How much of this would be happening with a steel chassis instead of something nonferrous?

    anbitet66

    Posts : 131
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by anbitet66 on Fri Jan 18, 2013 6:18 pm

    I'd suggest self-adhesive copper foil to line the interior and give a ground plane. I checked the prices at the one place I saw that sells 1.4 mil adhesive sheets in 18" widths by 5' length for $39.00 plus shipping. A pricy experiment for sure, but it could be the answer to this problem. Check out nimrodhall dot com.

    Tony


    Last edited by anbitet66 on Fri Jan 18, 2013 6:20 pm; edited 2 times in total (Reason for editing : Clean up messy thought.)

    Sal

    Posts : 223
    Join date : 2009-02-05
    Location : Central New Jersey Dynaco-ST70.com

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by Sal on Fri Jan 18, 2013 7:17 pm

    GP49 wrote:How much of this would be happening with a steel chassis instead of something nonferrous?

    +1.. I agree with GP49!

    Sal

    anbitet66

    Posts : 131
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by anbitet66 on Fri Jan 18, 2013 10:41 pm

    Sal,

    I also agree with GP49 but figure instead of tearing everything out and replacing the chassis, this is a possibility to still use the wooden chassis and to have a ground plane to reduce the hum. That is what DIY is all about. You try something different. If it works the first time, great Smile . If not Mad , you try some tweaks until it works to your satisfaction Cool .

    Just my 2¢.

    Tony

    GabrielG

    Posts : 11
    Join date : 2012-12-26

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by GabrielG on Sat Jan 19, 2013 9:38 am

    I moved the power supply to VTA even further and hum is now 5mv. Now it is acceptable.

    To continue improving it I will use microphone shielded wire.

    GabrielG

    Posts : 11
    Join date : 2012-12-26

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by GabrielG on Sat Jan 19, 2013 3:38 pm

    Just the shielding and connecting the ungrouded volume pot lowered volts by .0007. I will try grounding the shields of the wires and also the volume pot case.

    Sponsored content

    Re: New mk3 clone but Low humming (22mv) advice.

    Post by Sponsored content Today at 2:38 am


      Current date/time is Fri Sep 30, 2016 2:38 am