+ Reply to Thread
Page 6 of 7 FirstFirst ... 4567 LastLast
Results 51 to 60 of 70

Thread: 6J1 Pre-amp modifications (hum removal)

  1. #51
    Join Date: May 2008

    Location: Surrey

    Posts: 5,625
    I'm Rob.

    Default

    I got mine today. Have put a couple of hours on it and it sounds pretty decent.......far more decent than the paltry price tag (and fear of counterfeit parts) would suggest. I need to do the "hum" mod (although mine is making a sort of low level fizz) than hum.

    Question for Alan : Am I right to assume that this board uses a voltage doubler?
    Buy Bose...And get your parking validated!.

  2. #52
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 3,421
    I'm Alan.

    Default

    Yes Rob, it uses two voltage doublers to generate plus and minus 30V, so any hum component on the output is going to be at 50Hz, not the 100Hz from a full wave rectifier.


  3. #53
    Join Date: May 2008

    Location: Surrey

    Posts: 5,625
    I'm Rob.

    Default

    Quote Originally Posted by Firebottle View Post
    Yes Rob, it uses two voltage doublers to generate plus and minus 30V, so any hum component on the output is going to be at 50Hz, not the 100Hz from a full wave rectifier.

    Aha! I like my Saturday nights to have some FIZZZZZZ. Thanks Alan. Will do the "Hummmm/Fizzzzzz" mod soon.
    Buy Bose...And get your parking validated!.

  4. #54
    Join Date: May 2008

    Location: Surrey

    Posts: 5,625
    I'm Rob.

    Default

    I did the "hum" mod, but the fizz has been replaced with a..........hummmm hm? 50/60hz probably. I have disconnected one side of the 470uf cap (as I hot glued the cap to the board and might need to re-connect it - ?) Oddly the fizz has all but gone and there is only a very feint hum left. The cap has been left connected by it's NEG leg to the join of the 47r resistors only.
    Buy Bose...And get your parking validated!.

  5. #55
    Join Date: Oct 2012

    Location: The Black Country

    Posts: 3,421
    I'm Alan.

    Default

    Sounds a bit odd. You should have plus and minus about 30V from the voltage doublers if everything is working properly.

    Is it pretty close to 12V AC you are putting in? If it is 13V or more then the caps could be overrated.

  6. #56
    Join Date: May 2008

    Location: Surrey

    Posts: 5,625
    I'm Rob.

    Default

    Quote Originally Posted by Firebottle View Post
    Sounds a bit odd. You should have plus and minus about 30V from the voltage doublers if everything is working properly.

    Is it pretty close to 12V AC you are putting in? If it is 13V or more then the caps could be overrated.
    I measured the PS (a musical fidelity wall wart for an X-10D) and it was just over 13vac which I thought would be ok?

    Would it be worth changing the cap? It had been used before, but I am not aware that it was duff.
    Last edited by Puffin; 21-03-2017 at 08:12.
    Buy Bose...And get your parking validated!.

  7. #57
    Join Date: Nov 2010

    Location: Sheffield/Peak District. UK

    Posts: 333
    I'm Richard.

    Default

    Sorry to ask a daft question, but what is the difference, in this case, between the preamp version and the buffer version?
    Thanks,

  8. #58
    Join Date: May 2008

    Location: Surrey

    Posts: 5,625
    I'm Rob.

    Default

    The Preamp has gain, the buffer has no gain.
    Buy Bose...And get your parking validated!.

  9. #59
    Join Date: Nov 2010

    Location: Sheffield/Peak District. UK

    Posts: 333
    I'm Richard.

    Default

    Hi, thanks; so what's the point of a buffer?
    R

  10. #60
    Join Date: Feb 2013

    Location: W Lothian

    Posts: 32,983
    I'm Grant.

    Default

    Quote Originally Posted by Bonky View Post
    Hi, thanks; so what's the point of a buffer?
    R
    Impedence mismatching
    Regards,
    Grant ....
    Sometimes incompetence is useful. It helps you keep an open mind.
    .... ..... ...... ...... ................... ..... ..... ..... ..... .....
    IMUTO TAURUS X4 BATTERY SUPPLY. - RPI2B & AUDIOPHONICS DAC running MOODE 3.6- TONBRUX BATTERY SUPPLY & CHROMECAST2 AUDIO DONGLE no1 - JBE SERIES 3 SLATEDECK & EMOTIVA XPS-1 PHONO - DENON DV2900 & HEAVILY MODDED MF X10v3. BERESFORD SWITCHBOX. - TWIN PRO MONOBLOCK AMPLIFIERS. - XIANG SHENG DAC\PRE\HEADPHONE AMP. -AUDIO TECHNICA ATH-MSR7 HEADPHONES - WIN10 JRIVER22, SPOTIFY PREMIUM- OPPO PM-3 PLANAR HEADPHONES, KINPS CABLES, SMSL M6 MINIDAC, CHROMECAST2 AUDIO DONGLE no2 POWERED BY ANKER BATTERY PSU - FULL RANGE TWIN & SINGLE TELEFUNKEN's - TANDBERG TCD310 - CARTS.. AT95 Shibata, SHURE M55E original, JVC MD1029. - RCA CABLES BY BRIAN SPKR CABLES BY MOI HAIR BY MARCO FEET BY ELECTRICBEACH - MAINS REGENERATED BY POWERINSPIRED AND FILTERED BY BELKIN PUREAV.

+ Reply to Thread
Page 6 of 7 FirstFirst ... 4567 LastLast



 

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •