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    My new VTA 120, she sings!!!!

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    mcgyver74

    Posts : 74
    Join date : 2017-03-24
    Location : Jersey City, NJ

    My new VTA 120, she sings!!!!

    Post by mcgyver74 on Thu Apr 13, 2017 11:49 pm

    Ok, after many hours of work, my amp is finished.

    after a slight unknown with the resistance of the power cord, I plugged it in and flipped the switch....the 3 driver tubes started to glow so nicely! checked the heater voltages and they were right bang on!

    Ok, time for the big finish... Plugged in the rectifier and the left 2 output tubes as well as my speakers....realized I had messed up one of the pins of the tube socket (too much solder on the lug and it dribbled into the pin hole grrrrrr, the tube sits tight for now but I need to replace the socket at some point)

    Got the tubes in and flipped it on, the tubes started to glow... Checked my bias (I had already turned all bias pots fully counterclockwise per manual) and set each to .500 volts

    Turned it off, added the right output tubes and repeated...went between all 4 until they were nice and close to .500

    Then came the moment of truth. Plugged in my turntable, put the needle down...and AC/DC started coming out of my speakers Smile

    She sounds good. Did notice that when the record player is not playing and the stepped attenuator is wide open that there is a pretty noticeable hum, but when I unplug the RCA's to the turntable it goes away and the amp is dead quiet. I'll make a few shorting pins for the RCA's tomorrow and test it again but given that the caps in my turntable are from 1983 I am gonna say it's probably my record player Smile


    Feeling good!!!!!!

    Dogstar

    Posts : 233
    Join date : 2014-06-23

    Re: My new VTA 120, she sings!!!!

    Post by Dogstar on Thu Apr 13, 2017 11:58 pm

    Glad to hear you've had success. I too like AC/DC...saw them in 1981. Thanks to tubes my taste in music has expanded to also enjoying jazz and classical. To me tubes help music sound way more spacious.
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    sKiZo

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    Join date : 2013-04-01
    Location : Michigan USA

    Re: My new VTA 120, she sings!!!!

    Post by sKiZo on Fri Apr 14, 2017 12:18 am

    I forget ... does the stock power cord have polarized blades on it? Old school trick if you have some hum is to just reverse the plug in the socket. If the cord IS polarized, simple enough to just clip the ends of the wider blade so it fits.

    Another common problem is loose tabs holding the multi-cap to the chassis. Check for any wobble. Twist those nice and tight, and maybe solder an extra wire from that to one of the dedicated ground tabs.
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    Peter W.

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    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: My new VTA 120, she sings!!!!

    Post by Peter W. on Fri Apr 14, 2017 7:27 am

    sKiZo wrote:I forget ... does the stock power cord have polarized blades on it? Old school trick if you have some hum is to just reverse the plug in the socket. If the cord IS polarized, simple enough to just clip the ends of the wider blade so it fits.

    Next time SIT ON YOUR FINGERS!  Advising anyone to clip polarized plug blades is, well, the proper words for it are certainly not pleasant. The correct words are both unpleasant and vulgar.  I am sure that VTA would not promulgate a design that would hum when properly wired. Meaning that such a hum is an indication of a problem somewhere. The correct response would not be blade-clipping!

    Another common problem is loose tabs holding the multi-cap to the chassis. Check for any wobble. Twist those nice and tight, and maybe solder an extra wire from that to one of the dedicated ground tabs.

    At least this is good advice. There is this expression about blind squirrels....
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    Peter W.

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    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: My new VTA 120, she sings!!!!

    Post by Peter W. on Fri Apr 14, 2017 8:03 am

    Congratulations on a successful build!

    Well worth the effort, and you have learned much!
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    cci1492

    Posts : 76
    Join date : 2016-05-09
    Age : 56
    Location : Bergen County NJ

    Re: My new VTA 120, she sings!!!!

    Post by cci1492 on Fri Apr 14, 2017 8:47 am

    Congrats! My TT gives off a little noise too, no big deal once the music starts I can't hear it anyway. Enjoy!
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    deepee99

    Posts : 1595
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Congratulations, McGyver!

    Post by deepee99 on Fri Apr 14, 2017 10:56 am

    From Peter w.: "There is this expression about blind squirrels...." We learned a similar one about blind pigs and truffles.
    McG, turntable hum is the absolute bane of audio perfection. It has driven known Jehovah's Witnesses to forget how to ring door-bells, atheists to pray, and Mormons to drink coffee. It is pernicious: our black cat in the dark basement that isn't there.
    Let's assume all the above have been tried.
    My guess is it's in the cabling and/or grounding and their associated terminations. The signal from the highest-output phono cartridge is still the weakess in your system. It is therefore more susceptible to interference from nearby RF and AC sources than any other component. Keep your turntable leads as far away from AC runs as possible, or at least cross them at right-angles, and keep them as short as possible. Check those blonde frog-hair connections to the cartridge itself. Ground/unground the turntable to the phono pre-amp, and try that process as well between the phono and line preamp.
    There are no capacitors between the cartridge and the output RCA leads to my knowledge, so I doubt they're the problem.
    You say the turntable is 40 years old. The only caps I'm aware of that are used in a turntable involve motor speed control. But at that age the coax wiring could be a bit long in the tooth; try replacing it with new RCA ends.
    Again, congrats. You're deep in the red zone now!
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    j beede

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    Re: My new VTA 120, she sings!!!!

    Post by j beede on Fri Apr 14, 2017 11:47 am

    Maybe you can provide a bit more detail regarding your setup. What are you using for a phono stage? Could be a ground loop--any three prong plugs in your system? Bad juju.

    Buy a cheap power strip at Home Depot and cut the ground pin off the plug. Now plug all your gear into that strip. Hum? Then unplug one unit from the strip and plug it into the wall receptacle. This is a start.

    Since you have the input attenuator you can experiment with line level outputs directly plugged into the VTA-120 to see who likes to hum along with the music.
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    Peter W.

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    Location : Melrose Park, PA

    Re: My new VTA 120, she sings!!!!

    Post by Peter W. on Fri Apr 14, 2017 12:24 pm

    j beede wrote:Maybe you can provide a bit more detail regarding your setup. What are you using for a phono stage? Could be a ground loop--any three prong plugs in your system? Bad juju.

    Buy a cheap power strip at Home Depot and cut the ground pin off the plug. Now plug all your gear into that strip. Hum? Then unplug one unit from the strip and plug it into the wall receptacle. This is a start.

    Since you have the input attenuator you can experiment with line level outputs directly plugged into the VTA-120 to see who likes to hum along with the music.

    I think the hum/noise as-described is due to the larger gain on the phono pre-amp. Typically, if one turns up the gain to 100% on any phono section, a lot of noise is generated. This has nothing to to with the amp itself - which was described as dead-quiet when the phono section was not connected.

    mcgyver74

    Posts : 74
    Join date : 2017-03-24
    Location : Jersey City, NJ

    Re: My new VTA 120, she sings!!!!

    Post by mcgyver74 on Fri Apr 14, 2017 12:28 pm

    Smile Thanks everyone.

    I am planning to re-cap and replace the RCA's on my turntable as soon as I can find time to tear it apart and read the needed values to order (Hmm, project for this weekend meethinks) then I can order what I need from mouser or digikey and be sure.

    Yes the Cap's are for the variable motor control, one I THINK is actually a filter cap for the PS, but since I cannot find a schematic for this turntable for the life of me I am guessing until I trace the boards.

    For my phono stage I am using a Pro-Ject Tube Box DS Set for my Grado cart (I have a 2M Bronze in the box that I need to install one of these years).

    So the chain is:

    Turntable --> Tube Box DS --> VT120
    The turntable is grounded direct to the Tube Box...

    No 3 prongers in this setup,
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    Peter W.

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    Re: My new VTA 120, she sings!!!!

    Post by Peter W. on Fri Apr 14, 2017 12:39 pm

    mcgyver74 wrote:Smile

    Turntable --> Tube Box DS --> VT120
    The turntable is grounded direct to the Tube Box...  

    OK - back in the day when Vinyl was primary, such noted manufacturers as AR, Rabco, Thorens et.al. strongly recommended that the TT ground go to one of the line headshells. AR supplied their turntables with the ground to the left headshell, as I remember, so did Thorens. My Rabco TT came with the conventional loose ground, but in the instructions did suggest going to a headshell to 'reduce noise'.

    Just a thought.
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    peterh

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    Re: My new VTA 120, she sings!!!!

    Post by peterh on Fri Apr 14, 2017 12:46 pm

    mcgyver74 wrote::) Thanks everyone.

    I am planning to re-cap and replace the RCA's on my turntable as soon as I can find time to tear it apart and read the needed values to order (Hmm, project for this weekend meethinks) then I can order what I need from mouser or digikey and be sure.

    Yes the Cap's are for the variable motor control,  one I THINK is actually a filter cap for the PS, but since I cannot find a schematic for this turntable for the life of me I am guessing until I trace the boards.

    For my phono stage I am using a Pro-Ject Tube Box DS Set for my Grado cart (I have a 2M Bronze in the box that I need to install one of these years).

    So the chain is:

    Turntable --> Tube Box DS --> VT120
    The turntable is grounded direct to the Tube Box...

    No 3 prongers in this setup,  

    Spare your time "recapping" this turntable. It won't help the hum problem.
    Examine the cartridge shell for bad groundings, the cable from the arm to the rca plugs and finally the routing of cables. None of the cables should be close to AC,
    and the arm and pivot should have a proper grounding that is firmly conneced
    to the preamp.

    mcgyver74

    Posts : 74
    Join date : 2017-03-24
    Location : Jersey City, NJ

    Re: My new VTA 120, she sings!!!!

    Post by mcgyver74 on Fri Apr 14, 2017 1:29 pm

    Thanks I'll check the grounds Smile
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    Bob Latino
    Admin

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    Location : Massachusetts

    Re: My new VTA 120, she sings!!!!

    Post by Bob Latino on Fri Apr 14, 2017 1:31 pm

    mcgyver74 wrote:  but when I unplug the RCA's to the turntable it goes away and the amp is dead quiet.  I'll make a few shorting pins for the RCA's tomorrow and test it again but given that the caps in my turntable are from 1983 I am gonna say it's probably my record player Smile


    Feeling good!!!!!!

    If you unplug a source component going into your ST-120 amp and the amp is dead quiet as you say, then yes > there is a grounding issue with one of the source components in front of the VTA ST-120 like your turntable/preamp/phono preamp or the cabling between the components.

    Bob

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    deepee99

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    Re: My new VTA 120, she sings!!!!

    Post by deepee99 on Fri Apr 14, 2017 2:48 pm

    I'd start by leaving the Tube Box connected to the amp and shorting the Tube Box's inputs. See if the hum is still there. If not, then it's the TT-Tube Box connexion needing work. If it is, then you've got some issue with the Tube Box.
    Depending on the quality of the turntable and tonearm it might be worth re-wiring the tone-arm-cartridge connexion as well back to the terminal strip where coax meets tone-arm wires.

    mcgyver74

    Posts : 74
    Join date : 2017-03-24
    Location : Jersey City, NJ

    Re: My new VTA 120, she sings!!!!

    Post by mcgyver74 on Fri Apr 14, 2017 3:18 pm

    Yeah that's what I am now leaning towards, I don't need to ground my phono pre-stage to the amp correct?

    Dogstar

    Posts : 233
    Join date : 2014-06-23

    Re: My new VTA 120, she sings!!!!

    Post by Dogstar on Fri Apr 14, 2017 6:57 pm

    Next time I'm in a car that has a real bad knock from the pistons slamming into the lifters because the timing is way off I'll just tell the owner to crank up the volume on the radio.

    Solving the hum issue is the best thing to do.

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