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    Finished my PH15 but humming

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    Avinunca

    Posts : 26
    Join date : 2012-04-15
    Age : 59
    Location : Shrewsbury England

    Finished my PH15 but humming

    Post by Avinunca on Sat Jun 09, 2012 6:27 pm

    Well I have been building my PH15 for ages whenever I've found time but finally it's finished. Will post a picture.
    Great news is that after a couple of hours the sound is already very good indeed. I am hearing stuff I've not heard before from my albums. I am running a Pink Triangle 'Vectored' PT1 with Denon DL304 into a Graham Slee Elevator EXP
    step up amp into the PH15 then into a Unison Unico (valve/SS) hybrid integrated amp.
    The sound is big, detailed, the vocals particularly smooth and realistic. The imaging is spot on, something the EXP helps with.
    Just one hitch - mains hum even with no input cables connected. It is picking up hum from the house wiring. When I put the kettle on for example it increases in amplitude. The phono cabling in the PH15 is dual conductor screened with one leg tied to the screen at the pcb end. This applies to phono input and output cables. Can anyone see a problem with this or suggest why I am picking up so much stray mains. Amp is in a proper case same as Roy supplies.

    Photos are on the post below ...

    Michael

    Avinunca

    Posts : 26
    Join date : 2012-04-15
    Age : 59
    Location : Shrewsbury England

    Here's the photos

    Post by Avinunca on Sat Jun 09, 2012 6:33 pm

    Tried again with the pictures using the image icon






    danskman

    Posts : 17
    Join date : 2012-01-14
    Age : 57
    Location : Bière, Switzerland

    PH15 humming

    Post by danskman on Sun Jun 10, 2012 12:20 pm

    Hi!
    I tried to use hand-twisted pair of thin wire for the input and output, with no success to lower or suppress hum; then I used hi-Q shielded wire for the output (worse!!).
    I then use simple, non twisted, non-shielded tho wire for both input and output; hum is now nearly defeated.
    The best way to ground such a circuit is to separate low-life and "hi-level" signal ground (input and output) from power ground.
    That's the way I'll rebuild the wiring in mine, when I got time.
    Hum is not enoying me, because as soon as the diamond is touching the record, THE sound appears and nothing else exists anymore Wink
    hope it can help you,
    best regards,
    Danksman

    TMadden

    Posts : 99
    Join date : 2011-12-22

    Re: Finished my PH15 but humming

    Post by TMadden on Mon Jun 11, 2012 12:54 am

    Nice job building the PH15. I had a chance to hear one of these, I was VERY impressed!
    I might be able to help you with the hum problem if you can give me a little information.
    What is your AC line voltage, your "raw" B+ voltage (before the regulator) and your regulated B+ voltage?
    Where on the circuit board have you connected the 2 yellow/green wires from your AC power entry module?
    Is that Pro-Patch cable on the input and output shielded with foil or wire braid or is it twisted internally?

    Avinunca

    Posts : 26
    Join date : 2012-04-15
    Age : 59
    Location : Shrewsbury England

    Re: Finished my PH15 but humming

    Post by Avinunca on Mon Jun 11, 2012 5:15 am

    TMadden wrote:Nice job building the PH15. I had a chance to hear one of these, I was VERY impressed!
    I might be able to help you with the hum problem if you can give me a little information.
    What is your AC line voltage, your "raw" B+ voltage (before the regulator) and your regulated B+ voltage?
    Where on the circuit board have you connected the 2 yellow/green wires from your AC power entry module?
    Is that Pro-Patch cable on the input and output shielded with foil or wire braid or is it twisted internally?


    Screen is made from 96 x 0.10mm braided tinned oxygen free copper wire http://www.van-damme.com/14.html

    AC line voltage = 242V

    "raw" B+ voltage (before the regulator) = 230V

    and your regulated B+ voltage? = 218V

    I measured the output of the transformer HV too and it is only 205Vac. This is across yellow and white and I should apparently expect 220 VAC. The primaries connected in series for 230Vac are actually recieving 242Vac from my mains supply so I'm surprised I dont see more. I don't know what the tolerance is.
    Anyway the B+ Regulator is giving me 218V so that looks ok.


    I noticed that the anodes of V2 are only at 90V compared with the figure of 112V on the cct diagram


    I wasn't absolutely sure if the holes that provide paths from upper and lower pcb tracks could be 100% relied upon to
    provided a good electrical connection. I realise I haven't soldered anything through on two of them. I did check their conductivity from top to bottom at some point early on and they seemed to be good.
    I noticed on a photo that Roy did that jumpers had been run flush with the bottom of the pcb wheras I have stood mine off.
    I was also unsure about the grounding and ended running two wires back to the safety earth - one from the psu section and another from the amp section.

    I hope this is making sense to you!
    I appreciate your help.


    Michael

    TMadden

    Posts : 99
    Join date : 2011-12-22

    Re: Finished my PH15 but humming

    Post by TMadden on Mon Jun 11, 2012 7:48 am

    OK, I'm fairly certain the reason it is humming is that your B+ regulator requires a 15 to 20 volt difference between the input voltage and the output voltage in order to fully regulate and filter out the residual hum. You have only 12 volts. When you put the kettle on, your voltage drops a bit and aggravates the problem. The way to fix it is to lower the value of resistor R23 by about 5 or 10% to get the required differential. That will lower your B+ a bit but that's OK.
    Also, I have built a few of Roy's preamps and only use a single ground from the safety ground to the ground trace in the psu section and they are very quiet that way. My SP9 with PH14 phono pre built in is DEAD quiet except for tube hiss. No hum at all with moving coil cartridge! Again, nice job building the phono preamp and enjoy the fabulous sound!

    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: Finished my PH15 but humming

    Post by mantha3 on Mon Jun 11, 2012 9:49 am

    Phono premaps can really pick up tube hum... Do you have any spare tubes you could try to swap out just to see if the hum changes for the better?

    Avinunca

    Posts : 26
    Join date : 2012-04-15
    Age : 59
    Location : Shrewsbury England

    Re: Finished my PH15 but humming

    Post by Avinunca on Mon Jun 11, 2012 12:13 pm

    TMadden wrote:OK, I'm fairly certain the reason it is humming is that your B+ regulator requires a 15 to 20 volt difference between the input voltage and the output voltage in order to fully regulate and filter out the residual hum. You have only 12 volts. When you put the kettle on, your voltage drops a bit and aggravates the problem. The way to fix it is to lower the value of resistor R23 by about 5 or 10% to get the required differential. That will lower your B+ a bit but that's OK.
    Also, I have built a few of Roy's preamps and only use a single ground from the safety ground to the ground trace in the psu section and they are very quiet that way. My SP9 with PH14 phono pre built in is DEAD quiet except for tube hiss. No hum at all with moving coil cartridge! Again, nice job building the phono preamp and enjoy the fabulous sound!

    Sounds like a good strategy. Will give it a try and let you know how it goes. I will also experiment with the V1 grid battery bias or film cap bypass when this is sorted out. Thanks

    Avinunca

    Posts : 26
    Join date : 2012-04-15
    Age : 59
    Location : Shrewsbury England

    Re: Finished my PH15 but humming

    Post by Avinunca on Mon Jun 11, 2012 12:20 pm

    mantha3 wrote:Phono premaps can really pick up tube hum... Do you have any spare tubes you could try to swap out just to see if the hum changes for the better?

    Will see if I have any spares after I have tried adjusting the B+ V controller if that doesn't help. I suspect it will though as the hum shoots right up when my ring main is under more load. I think it also happens when my neighbor is using heavy current appliances or maybe the local supply voltage varies. Thanks

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Finished my PH15 but humming

    Post by tubes4hifi on Tue Jun 12, 2012 12:17 pm

    yes, Troy is 100% correct, the most likely problem is that the B+ regulator doesn't have enough voltage across it to work properly, you need about 20v difference between input and output. Decrease your R23 value by about 5% and expect some magic to happen, like no hum at all, and dead quiet.
    If you have 218vdc you probably are using 270K. I use 249K now for all kits and builds, for 201vdc output.
    A customer in Australia with 230vac 50Hz is having to change to 236K as the input to the regulator is even lower than yours.
    It also seems some of the more recent toroid transformers aren't putting out quite their rated voltage.

    Alan-14

    Posts : 46
    Join date : 2012-03-31
    Age : 56
    Location : Melbourne - Australia

    Re: Finished my PH15 but humming

    Post by Alan-14 on Wed Jun 13, 2012 11:46 am

    That would be my PH-15 thats also humming

    Roy has just sent off another pair of resistors ... so when they arrive I'll be breaking out the soldering iron again and saying goodbye to this hum Smile

    Avinunca

    Posts : 26
    Join date : 2012-04-15
    Age : 59
    Location : Shrewsbury England

    Re: Finished my PH15 but humming

    Post by Avinunca on Fri Jun 15, 2012 4:28 pm

    Very Happy Very Happy Very Happy Very Happy Very Happy NO MORE HUMMING

    Just sweet music. I changed the resistor costing about 2p and all I have now is wonderful music.
    Just been listening to Ella and Satchmo together and the vocals are so smooth and realistic. Like having them in the room. The trumpet too - all the timbre.

    Thanks guys and well done Roy

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