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  1. #1
    Forum Regular Audioman00's Avatar
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    May 2002

    Question Bias adjustment in an amp....need advice from the techs

    I have an older model Yamaha receiver (one of the better ones) and I noticed a couple of little riostats or potentiometers right next to the output transistors (seems to be one for every channel) and wondered if this is the bias adjustment? or maybe a gain level? I dunno, I was hoping to catch a tech on this site and find out if it can be beneficial to adjust these in any way. Thanks for any advice!

  2. #2
    Phila combat zone JoeE SP9's Avatar
    Join Date
    Jun 2003
    Philadelphia, PA
    They are probably level controls. Bias on solid state gear is usually not adjustable. On tube amps it is almost a requirement. When output tubes are replaced the bias is adjusted to provide equal current flow through the tube pairs.
    ARC SP9 MKIII, VPI HW19, Rega RB300
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    Front: Magnepan 1.7, DBX 223SX, 2 modified Dynaco MK3's, 2, 12" DIY TL subs (Pass El-Pipe-O) 2 bridged Crown XLS-402
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  3. #3
    DIY Dude poneal's Avatar
    Join Date
    Sep 2003
    TX, USA

    Put this on the PE tech forum

    There are quite a few EEs that frequent the site and will be able to provide you with more info. Regards, Paul.

  4. #4
    Forum Regular
    Join Date
    Dec 2004
    Toronto, Ontario
    without looking at the circuit, i couldnt tell you. it could be a great many things. what model of receiver is it?


  5. #5
    Forum Regular
    Join Date
    Feb 2003

  6. #6
    Forum Regular
    Join Date
    Aug 2004
    Try post at

    The people there will almost certainly recommend you get a service manual rather than play... but there is a vintage Yamaha following there - if your amp is in that league there might be someone who can give you instructions.

    I wouldn't recommend you play and see how it goes - you're likely to make it worse without a service manual.


  7. #7
    Forum Regular Audioman00's Avatar
    Join Date
    May 2002
    I blew it up shortly after posting this....ha ha... I decided to turn the bias all the way up while it was on..lmao and BANG!! dead yamaha... man I was dumb

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