Amplifier Distortion, DC-Offset, and You!

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

  1. Shrugg

    Shrugg New Member

    Messages:
    37
    Location:
    Woodland Hills, Los Angeles, CA
    Harman kardon hk 460i
    Left channel- 65mv
    Right -110mv
    No wonder why it sounded so muddy! Probably should’ve checked before using it. Thankfully, this amp has an offset adjustment, so it shouldn’t be too bad.
     

     

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  2. Shrugg

    Shrugg New Member

    Messages:
    37
    Location:
    Woodland Hills, Los Angeles, CA
    Lol, forgot about the decimal point and that I had turned down the treble. :confused:
    Harman kardon hk 460i after idling for an hour
    Left- 19.2
    Right- 17.6
     
  3. LWB

    LWB AK Subscriber Subscriber

    Messages:
    311
    Location:
    Calgary, Alberta, Canada
    Rotel RB-980BX power amp. Manufactured in 1994. Left channel measures 13.7mV, right channel measures 13.6mV.
     
  4. Rog50

    Rog50 Active Member

    Messages:
    306
    Location:
    Ontario
    Technics SU-V9 (Was serviced 2 years ago)
    R = 1.8
    L = 0.9

    Yamaha CR240 Untouched bottom of the line receiver
    R = 21.5
    L = 19.6 (took a while to settle down on the left channel, dropped from 20.2 over a few minutes)
     
  5. JMiP

    JMiP AK Subscriber Subscriber

    Messages:
    282
    Location:
    North Carolina
    JVC JA-S77

    R: 5mV
    L: 3.5mV
     
  6. Rockon1

    Rockon1 Well-Known Member

    Messages:
    581
    Rotel RA2030

    Right 4.5mv

    Left fluxuates slightly but is negative 2.9 mv -unless I reverse the leads (Neg to pos and vice versa) ? Bob
     

     

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  7. Trodder

    Trodder New Member

    Messages:
    39
    My Fisher CA-880 that is going to undergo some fixes and enhancements is as follows:

    Left A Channel Reading = 37.7mv after 1 minute
    Right A Channel Reading = 38.5mv after 1 minute

    Both seemed to stabilize after about a minute with no load on the channels. The intial reading when the protection relay kicks it hits 150mv + or - on each than drops rapidly to the specified values and seems to be stable there after only a minute or so.

    I will report back with my Nikko -NA-850 (current live system) once I get a change to test that
     
  8. KrautNotRice

    KrautNotRice AK Subscriber Subscriber

    Messages:
    399
    Location:
    South Carolina
    Very helpful thread, thanks to EW for starting it.
    I just tested 3 of my amps with multimeter set to 200mv DC:

    Yamaha CR-1020 R: 2.5 L: -0.7
    Yamaha P2200 R: 21.5 L: 20.1
    Teac A-H500 R: 18.1 L: 49 !!!!!!

    The craziest thing is that the Teac still sounds AMAZING as is. Just shot out all 3 amps back to back with the same cd and the Teac is fantastic, with the P2200 a close second.
    Maybe it's time for a service and it'll be even better?
     
  9. Saltydog

    Saltydog New Member

    Messages:
    19
    OK, Hi Echowars.
    I bet you had NO idea how long THIS thread would go on!
    So, 226 pages, WOW!
    So I just picked up an Audire Parlando.
    Not much out there on the web and I'm still evaluating its functionality, but its working.
    I came across your thread at some point and it couldn't be any timelier!
    So here's my 2 cents.
    This amp takes a Looooong time to stabilize (45min-1 hr) and I may have taken these readings a little prematurely (35 min.)

    I measure 29.9-32.2 for my R. channel & -.6/+3 for the L.
    The range is due to a slow variation which I assume is it's thermal state stabilizing.
    I'm not sure though, The L. channel is the one I was more concerned with as this amp has a bunch of independent heat sinks per channel and there's a lot of variation on the L. channel.
    Not too bad considering it was a blind purchase! Leaves me room to tinker, no?
     
  10. DAA

    DAA Active Member

    Messages:
    107
    Sony TA F700ES

    R: 2.3
    L: 6.1

    Pretty good! I’ll dial them to 5.0 as per service manual spec next cleaning
     
  11. rgbeach

    rgbeach AK Subscriber Subscriber

    Messages:
    148
    Location:
    Palos Heights, IL
    Adcom GFA-535II, recently refurbished using kits from Chris Hoppe (https://hoppesbrain.com/), including replacing the power supply board and critical components on both amp boards, notably both pairs of input transistors with closely matched pairs.

    R Ch.: 0.2 mVDC
    L Ch.: 0.4 mVDC
     
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  12. starcopy

    starcopy AK Subscriber Subscriber

    Messages:
    201
    Location:
    NE Ohio USA
    Nakamichi TA-2A: Both channels at -39mv. I wonder if it can be adjusted?
     
  13. tippyd

    tippyd New Member

    Messages:
    31
    Hello I can here static/distortion in left channel. I read like first 10 pages of this discussion and decided to see how my circa 1994 pioneer vsx 453 receiver faired. DC offset Left 90mv and Right 6mv. I guess I need to find resistors for the left side. I'm very new at this anyone have pics of resistor locations and maybe have a how to/diy of someone doing a similar fix. TIA
     
  14. bill114

    bill114 AK Subscriber Subscriber

    Messages:
    279
    Location:
    Seminole, FL
    The service manual is available here: https://www.hifiengine.com/. It's free to join.
     
  15. Gibsonian

    Gibsonian Super Member

    Messages:
    3,469
    Location:
    Iowa
    Best thread in the free world possibly.

    Don't let offset distortion get you down man!
     
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  16. bill114

    bill114 AK Subscriber Subscriber

    Messages:
    279
    Location:
    Seminole, FL
    When matching transistors in differential pairs, does the gain of each pair need to match the gain of the other?
     

     

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  17. rcs16

    rcs16 Super Member

    Messages:
    3,723
    Location:
    Baldwin, Ontario, Canada
    Each pair should match but not required to match the other diff pairs.
     
  18. bill114

    bill114 AK Subscriber Subscriber

    Messages:
    279
    Location:
    Seminole, FL
    thank you!
     
  19. rcs16

    rcs16 Super Member

    Messages:
    3,723
    Location:
    Baldwin, Ontario, Canada
    I was looking at the 2sa798 data sheet yesterday, they state that Vbe is matched to typ = 1mV, max 10mV.
     
  20. The Rebel

    The Rebel Active Member

    Messages:
    300
    Location:
    Deep South
    Pioneer SX-1250
    Right = 1.1mV
    Left = -2.3mV
    How bad do I need to worry about the negative reading, and is it something that would be detrimental to mids and tweeters? This receiver has never been re-capped, is very clean inside, and sounds amazing. Is it a candidate for a re-cap, or keep rocking as is? Thanks for the thread Echowars!
     

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