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


    Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Share

    oldsmobuick

    Posts : 12
    Join date : 2015-03-19

    Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by oldsmobuick on Sat Apr 02, 2016 9:41 am

    I have recently finished rebuilding a PAS3 using the tube nirvana ultimate upgrade kit consisting of the PH10 phono board and the Aikido line stage along with the fully regulated (v23) power supply.

    The line stage sounds great but the phono has a pronounced hum at normal listening level (9 o'clock). Holger at TN has given me some suggestions but I find myself stumped, hoping for some more tricks from the group. Tubes in phono stage are brand new 12AY7 JJ.

    Here's what I've checked so far:

    1. Flip power plug over.
    2. Turn off any dimmer/flouro/halaogen lights.
    3. Move preamp away from other equipment, unplug other sources than turntable.
    4. Try a variety of RCA interconnects.
    5. Use shorting pins at phono in to isolate source of hum: hum still present.
    6. Does hum follow volume? Yes.
    7. Check for redundant ground wires: only one ground attached on Aikido line board IN and OUT.
    8. Check that phono RCA grounds are not shorted to chassis.
    9. Verify wiring/grounding of Volume/balance pots.
    10. Reflow all solder points on PH10 PCB
    11. Replace filament wires and power switch with 20ga stranded wire (was 24ga) double-checked all PS wiring at this time
    12. Prod/poke wiring runs with plastic stick to see if hum changes as wires are moved (hum stays same)
    11. Cleaned bottom of boards of any residue/solder debris


    Have not tried:
    Replace 12AY7 tubes (I currently only have these two, new JJ tubes)
    Different power amp (hoping to try this today)

    Pics are here (shown before smaller wire was replaced with 20ga to F+/- and power switch):
    https://www.icloud.com/sharedalbum/#B0fGf693ZBuOfR

    Sometimes it takes a few seconds for them to come into focus after clicking on them for some reason.

    Thanks for any assistance!

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by peterh on Sat Apr 02, 2016 9:52 am

    oldsmobuick wrote:I have recently finished rebuilding a PAS3 using the tube nirvana ultimate upgrade kit consisting of the PH10 phono board and the Aikido line stage along with the fully regulated (v23) power supply.

    The line stage sounds great but the phono has a pronounced hum at normal listening level (9 o'clock). Holger at TN has given me some suggestions but I find myself stumped, hoping for some more tricks from the group. Tubes in phono stage are brand new 12AY7 JJ.

    Here's what I've checked so far:

    1. Flip power plug over.
    2. Turn off any dimmer/flouro/halaogen lights.
    3. Move preamp away from other equipment, unplug other sources than turntable.
    4. Try a variety of RCA interconnects.
    5. Use shorting pins at phono in to isolate source of hum: hum still present.
    6. Does hum follow volume? Yes.
    7. Check for redundant ground wires: only one ground attached on Aikido line board IN and OUT.
    8. Check that phono RCA grounds are not shorted to chassis.
    9. Verify wiring/grounding of Volume/balance pots.
    10. Reflow all solder points on PH10 PCB
    11. Replace filament wires and power switch with 20ga stranded wire (was 24ga) double-checked all PS wiring at this time
    12. Prod/poke wiring runs with plastic stick to see if hum changes as wires are moved (hum stays same)
    11. Cleaned bottom of boards of any residue/solder debris


    Have not tried:
    Replace 12AY7 tubes (I currently only have these two, new JJ tubes)
    Different power amp (hoping to try this today)

    Pics are here (shown before smaller wire was replaced with 20ga to F+/- and power switch):
    https://www.icloud.com/sharedalbum/#B0fGf693ZBuOfR

    Sometimes it takes a few seconds for them to come into focus after clicking on them for some reason.

    Thanks for any assistance!

    Is the chassies properly grounded ? And all sides are mounted and fastened correct ?

    oldsmobuick

    Posts : 12
    Join date : 2015-03-19

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by oldsmobuick on Sat Apr 02, 2016 9:57 am

    Yes I'm testing the hum with the top and bottom cases fastened on. And PS is grounded to chassis. The PC boards get their grounds from PS.

    peterh

    Posts : 642
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by peterh on Sat Apr 02, 2016 11:02 am

    oldsmobuick wrote:Yes I'm testing the hum with the top and bottom cases fastened on. And PS is grounded to chassis. The PC boards get their grounds from PS.
    And what are the ground of the chassies ? Nothing ? Hanging "in the air " ?

    Ground is something connected to earth outside :-) Usually distributed to the third
    connector, if it's missing you may have to improvise.

    Same ground should probably also connect other equipment, with one exception :
    anything connected with cable-TV should be separated with a "ground interrupter" or
    else a nasty ground-loop might happen.

    oldsmobuick

    Posts : 12
    Join date : 2015-03-19

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by oldsmobuick on Sat Apr 02, 2016 2:17 pm

    peterh wrote:
    oldsmobuick wrote:Yes I'm testing the hum with the top and bottom cases fastened on. And PS is grounded to chassis. The PC boards get their grounds from PS.
    And what are the ground of the chassies ? Nothing ? Hanging "in the air " ?

    Yes, this design uses a two pronged power plug (retro-fits into an old chassis). In any case, I tried grounding the chassis to house earth as a test but the hum was unchanged.

    GP49

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

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by GP49 on Sat Apr 02, 2016 5:09 pm

    oldsmobuick wrote:Have not tried:
    Replace 12AY7 tubes (I currently only have these two, new JJ tubes)

    Regardless...did you try swapping tubes between channels to see if the hum "follows" a tube?

    This assumes that those boards use both halves of each tube for one channel, and both halves
    of the other tube for the other channel. I'm not sure how those boards do it; the stock Dynaco
    circuit does it that way.

    oldsmobuick

    Posts : 12
    Join date : 2015-03-19

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by oldsmobuick on Sat Apr 02, 2016 5:35 pm

    GP49 wrote:
    oldsmobuick wrote:Have not tried:
    Replace 12AY7 tubes (I currently only have these two, new JJ tubes)

    Regardless...did you try swapping tubes between channels to see if the hum "follows" a tube?

    Thanks for the suggestion, I did swap the position of the tubes on the phono board and the hum still comes equally from both channels.

    nmchiefsfan

    Posts : 33
    Join date : 2012-03-21

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by nmchiefsfan on Tue Apr 05, 2016 12:21 pm

    I had a pretty bad hum when I built my ST-120. It turned out to be the center 12AT7 tube. It was a Brand New JAN Phillips. I replaced it with a tested quiet Mullard 4024 (ECC81) and the problem cleared right up. Do you have access to any replacements that you could "Borrow"? It may be worth contacting Jim McShane or Upscale Audio to see how much a tested quiet tube would cost.

    oldsmobuick

    Posts : 12
    Join date : 2015-03-19

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by oldsmobuick on Tue Apr 05, 2016 12:22 pm

    nmchiefsfan wrote:Do you have access to any replacements that you could "Borrow"?

    Thanks for the note, I'll track down a couple of known-good tubes and try that next!

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by MontanaWay on Sun Apr 10, 2016 3:35 pm

    No, I did not change the design of the PH10 pcb as far as 'lifting' the filament supply is concerned, that would be a silly thing to do!
    In fact, I improved the pcb design by eliminating the need to use jumper links as well as having both channel components placed in identical positions to make assembly easier and more logical, as well as adding a proper pcb ground plane on both sides of the pcb.
    We need to be very careful here when making such statements, it is always best to first contact me if one is unsure!


    Last edited by MontanaWay on Sun Apr 10, 2016 8:06 pm; edited 1 time in total

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by MontanaWay on Sun Apr 10, 2016 3:40 pm

    so olds, have you been able to rectify your hum issues?
    I am currently in Australia visiting family, so it may take some time for me to reply here, due to the time difference.

    Sponsored content

    Re: Chasing Down a Hum in PH10 Phono Stage (Pics included)

    Post by Sponsored content Today at 4:24 am


      Current date/time is Thu Sep 29, 2016 4:24 am