Amplifier Distortion, DC-Offset, and You!

Discussion in 'Solid State' started by EchoWars, Mar 19, 2003.

  1. cferry1

    cferry1 Member

    Messages:
    67
    Agree. I higher DC Balance Offset Voltage and higher Idle Current Adjustment will result in much higher temperature Output Final Power Transistor's. The Heatsink Fins as well.
     
  2. bikehomero

    bikehomero Active Member

    Messages:
    130
    Location:
    Frankfurt am Main - Germany

    Solved the problem today. It was the transistor Q601. Changed it from the left channel an DC was at 30mV. At the left side i replaced the konw missing Q501 with a BC547 resulting in 17mV DC.
     
  3. sootboots

    sootboots New Member

    Messages:
    32
    Recently acquired Sansui AU-9900. Left 6mv right 15mv. That is good enough for me. How often should this be checked?

    Jp
     
  4. LTD428CJ

    LTD428CJ New Member

    Messages:
    2
    Sansui 5000. 23.6 - left, 24.2 - right. These were "peak" numbers seen rarely.
     
  5. ernestas0001

    ernestas0001 New Member

    Messages:
    3
    Hi !

    My Harman Kardon HK 3490 gives ok results:

    L 25
    R 21

    I have set trimpots as close as possible to 21.12 as manual stated. Probably I will need to look closer into hardware.
     
  6. redk9258

    redk9258 Super Member

    Messages:
    1,277
    Location:
    Illinois, close to St. Louis.
    Are you confusing bias with DC offset? Be careful if you aren't 100% sure of what you are adjusting. You WILL blow up the output transistors along with other stuff.
     
  7. ernestas0001

    ernestas0001 New Member

    Messages:
    3
    Yes, I think I might be mixing up the things ! Anyways, I haven`t played with them, simply adjusted to correct values according to the manual as they seemed to drift away.
    Now, how could I decrease milivolt values on speaker connectors on HK 3490 ?
     
  8. Eastham

    Eastham More Class-A than ever!

    Messages:
    1,606
    Location:
    Liverpool, UK
    Well it's been a few months since I recapped my Sherwood S-8910 and here's the DC offset readings as of today; 4.5mV left, 11mV right.
     
  9. Powertech

    Powertech Member

    Messages:
    95
    Location:
    South Wales, U.K.
    My Rotel RB976 (6 channels) range from 4.1mV to 8.4 mV. They are running quiescent currents of about 90mA per channel. It runs slightly warm, but it does sound better than the factory recommendation.
     
  10. Olecranon

    Olecranon Active Member

    Messages:
    159
    Do you need a preamp connected to the amplifier to get a "true" reading, or can this be done with the preamp disconnected?

    I check my Rotel RB-980BX after leaving it on for 15 minutes.

    L - 1.1mV
    R - 8.6mV
     
    Last edited: Nov 18, 2017
  11. Vaylo

    Vaylo New Member

    Messages:
    1
    My Onkyo A-22: left 11.5mV, right 12mV.
     
  12. dhmcclain1

    dhmcclain1 AK Subscriber Subscriber

    Messages:
    13
    Location:
    Lancaster County, PA
    Sherwood S-7200. Just purchased for $20. Left channel::0.0mv. Right channel: 42mv. When listening (headphones, haven't hooked it to speakers), right channel is "static-y" and distorted.
    Also, inadvertently touched two control knobs at the same time and got a lovely hum in the right channel. Be gentle, as I am a newb:), but I presume this indicates a ground issue? For the hum, at least?
     
  13. Beau Geste

    Beau Geste Super Member

    Messages:
    3,493
    Location:
    Italia
    First of all get a manual service .You can find it here : https://elektrotanya.com/sherwood_s-7200_sch.pdf/download.html :After this give look to find the trimmer to set up the DC offset .The left channel seems OK you have to worl to right channel only . Here you can find a lot of advices to proceed...On AK we have the MASTER of Offset...
     
  14. Powertech

    Powertech Member

    Messages:
    95
    Location:
    South Wales, U.K.
    Measure the DC offset at the speaker terminals with everything disconnected and volume at maximum (select a line input if using an integrated amp).
     
  15. redk9258

    redk9258 Super Member

    Messages:
    1,277
    Location:
    Illinois, close to St. Louis.
    Volume at minimum, not maximum .
     
  16. RobinTW

    RobinTW Member

    Messages:
    58
    Location:
    Taipei, Taiwan
    Sony TA-F222ESR
    R Channel: 32.5 mV; L Channel: 28.5mV
    Both are not good.
    I also notice a strange thing. My readings are actually negative. I am sure the connections are correct. Any explanation?
     
  17. RobinTW

    RobinTW Member

    Messages:
    58
    Location:
    Taipei, Taiwan
  18. claybar

    claybar New Member

    Messages:
    28
    Location:
    Ohio
    Craig Series 5000 Model # 5504 .

    Left 8.0 mv
    Right 1.4 mv
     
  19. RobinTW

    RobinTW Member

    Messages:
    58
    Location:
    Taipei, Taiwan
    My newly purchased Sansui AU-D907 (919's Japanese model name)
    Was Left 23.5mV, Right 6.5mV
    Now Left 2.5mV, Right 2mV after Bias and DC offset adjustment. :)
     
  20. DAA

    DAA Member

    Messages:
    57
    Sony TA F700ES

    Right: 6.5mv
    Left: 3mv

    Pretty solid!!
     

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