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Canceling the balance pot on Harman Kardon receiver

Discussion in 'Repairing Electronics' started by QuiqueM, Jun 2, 2018.

  1. QuiqueM

    QuiqueM New Member

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    Hi,
    I have a Harman Kardon AVR30 receiver, which is about 20 years old. It still works perfectly, but the balance potentiometer cuts off on certain parts of its travel.
    This is the second time it fails. The first time I repaired it myself, by replacing the pot with a similar one, but several years later fails again. I wish to cancel the balance function, since I never use it.
    Please refer to attached schematic, with balance pots marked VR501/502. If I remove then, can I leave an open circuit? or do I replace them by fixed resistors?

    I would be grateful if you could advise me.
     

    Attached Files:

  2. crutschow

    crutschow Well-Known Member Most Helpful Member

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    Below is a schematic clip of the pot's circuit.
    What you replace them with depends upon what the pot settings are normally when using those inputs.

    They appear to be dual pots, so if they are normally set at the 50% point (half-way between the pot extremes), then just replace the pots with two 24.9kΩ ±1% resistors in series to ground, with the output taken from the junction of the two resistors.

    upload_2018-6-2_9-10-33.png
     
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Just disconnect the pot entirely, and wire from R501 to FL, and R502 to FR.

    No need to put resistors in (it might be slightly louder, but that's what the volume control is for), and if you did they would't be 50/50 as the pot will be log/anti-log - 50/50 would make little difference.
     
  4. dave miyares

    Dave New Member

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  5. QuiqueM

    QuiqueM New Member

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    Thank you Gents for your good tips. I will try Nigel's first and see how it goes.
     
  6. unclejed613

    unclejed613 Well-Known Member

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    balance pots are so seldom used (by the user). you could just jumper the wipers to the signal end of each pot.
     
  7. QuiqueM

    QuiqueM New Member

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    Hi Uncle, thanks for your tip, but I'm not an electronics dud and the only wipers I know are those cleaning my car windscreen. Do you mean I do like Nigel suggested: "Just disconnect the pot entirely, and wire from R501 to FL, and R502 to FR."
     
  8. dave miyares

    Dave New Member

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  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Yes he does, the wiper is the centre contact (the little arrow on the symbol) that 'wipes' along the track.
     
  10. QuiqueM

    QuiqueM New Member

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    Hi Nigel, thanks again. But just to play it 100% sure and before I open the unit: if I got it right, I must open the connections in red and rewire them like indicated in green. My question is what to do with the pot end showed with the blue arrows, should I keep it connected, or should I leave it open and floating?
     

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  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    That's fine, leave the pot slider floating, and leave the outer two connections in place as it might require the DC connection through the pot.
     
  12. QuiqueM

    QuiqueM New Member

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    So, it will look like this:
     

    Attached Files:

  13. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Yes, that's perfect.
     
  14. QuiqueM

    QuiqueM New Member

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    Hi Gents,
    I carried out my mod yesterday. It took me a while because the receiver's box is quite tricky to open, with most control pots fixed onto a PCB. I shorted the balance pots as you guys suggested and it works perfectly fine, the balance control is now cancelled and sound levels are equal between both channels. Thanks again for the advice.
     
  15. unclejed613

    unclejed613 Well-Known Member

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    it's always been my opinion that power amplifiers should have no controls except a power switch. all of the control of signal levels, tone/balance/source etc... should be in the preamp. with controls in the amp, you have too much room for human error, such as turning the amp gain down in the amp, and wondering why the preamp no longer drives the amp properly.
     
  16. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Perhaps you haven't read the entire thread?, we aren't talking about separate preamps and power amps, (which are really pretty uncommon - and usually wouldn't have any controls on the power amp anyway) but an integrated amplifier, like almost all are.
     

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