Amplifier Distortion, DC-Offset, and You!

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

  1. 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
     

     

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  2. LTD428CJ

    LTD428CJ New Member

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

    ernestas0001 New Member

    Messages:
    6
    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.
     
  4. redk9258

    redk9258 Super Member

    Messages:
    1,388
    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.
     
  5. ernestas0001

    ernestas0001 New Member

    Messages:
    6
    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 ?
     
  6. Eastham

    Eastham More Class-A than ever!

    Messages:
    1,914
    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.
     

     

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  7. Powertech

    Powertech Active Member

    Messages:
    329
    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.
     
  8. Olecranon

    Olecranon Active Member

    Messages:
    163
    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
  9. Vaylo

    Vaylo New Member

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

    dhmcclain1 AK Subscriber Subscriber

    Messages:
    16
    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?
     
  11. Beau Geste

    Beau Geste Addicted Member

    Messages:
    8,966
    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...
     

     

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  12. Powertech

    Powertech Active Member

    Messages:
    329
    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).
     
  13. redk9258

    redk9258 Super Member

    Messages:
    1,388
    Location:
    Illinois, close to St. Louis.
    Volume at minimum, not maximum .
     
  14. RobinTW

    RobinTW Member

    Messages:
    59
    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?
     
  15. RobinTW

    RobinTW Member

    Messages:
    59
    Location:
    Taipei, Taiwan
  16. claybar

    claybar New Member

    Messages:
    29
    Location:
    Ohio
    Craig Series 5000 Model # 5504 .

    Left 8.0 mv
    Right 1.4 mv
     

     

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  17. RobinTW

    RobinTW Member

    Messages:
    59
    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. :)
     
  18. DAA

    DAA Active Member

    Messages:
    103
    Sony TA F700ES

    Right: 6.5mv
    Left: 3mv

    Pretty solid!!
     
  19. Chaulk61

    Chaulk61 New Member

    Messages:
    17
    Yamaha cr 820

    R: 11.8
    L: 11.6
    But I went to measure idling current, and get readings of 0 on both left and right. How can this be or what am I doing wrong? Red to tp1 - black to tp2 - receiver on for 10 mins, speakers off, aux selected, vol at Minimum
     
  20. desertrat748

    desertrat748 Active Member

    Messages:
    171
    Purchased an refurbished Sansui 661 from local shop. Decent sound but decided to check the offset after warming it up.
    Before: R: 22~28 mV
    L: 55~58.5 mV

    After adj: R: 2.1 ~ 4.8 mV
    L: 0.8 ~ 2.6 mV

    I still love the sound of this old SS receiver and my mind says it sounds even better now. EDIT: I listened to the Sansui for hours yesterday. Didn't believe it could sound so much better! Unreal now. THANK YOU Echowars!

    Checked an old Kenwood KR-5060 that powers up the kitchen turntable over some vintage Sansui speakers (don't laugh, it's just for making coffee and toast in the mornings). This thing sounds really clean and clear, maybe it's because of decent DC offset?

    R: 2.2 mV to 4.5mV
    L: -1.9 mV to 2.6 mV


    Fisher CA-880 amp (has a Darlington pair and can't find where to adjust it). Still sounds really decent though. Clean.

    R: 48.2 mV
    L: 52.1 mV

    Only with the Sansui does the offset mV swing around and fluctuates a lot even when it is really warmed up but it looks like that's okay. This thread is huge and I've only read up to the first 160 pages or so although I jumped to the end to see what's been happening. Thanks Echo for starting and sharing your knowledge!
     
    Last edited: Dec 18, 2017

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