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Lin or log potentiometers ? [A&R A60]

Discussion in 'd.i.y.' started by istari_knight, Jan 24, 2013.

  1. istari_knight

    istari_knight pfm Member

    I'm preparing to service a circa 1984 [issue 3] A&R A60, the balance control no longer works correctly on the right channel & they all feel a bit knackered so thought it worth fitting new ones as they're so cheap.

    Problem is I haven't changed a potentiometer before & cant be certain which ones I need - Log or Lin ?

    The volume control is 20K-D-X2 which I guess means 20K-Log-Dual I don't know what the D means but all volume controls are Log right ? The bass/treble/balance potentiometers are 20K-B-X2 which I think means 20K-Lin-Dual... Please can someone confirm / put me right ?

    Thanks in advance :)
     
  2. andyr

    andyr Registered User

    I've just gone through the process of sourcing a balance control. From what I read, they are all linear (in contrast to volume pots which are generally log). :)

    Regards,

    Andy
     
  3. david ellwood

    david ellwood Kirabosi Kognoscente

    for an improvement in sound quality and reduction in inaccurate balance just solder a pair of precision welwyns over the pads and remove the pot altogether.
     
  4. DuncanF

    DuncanF pfm Member

    From the service manual: the volume is 100K log dual, the bass, treble and balance are 22K linear dual. That is consistent across all the versions covered in the manual. If I get time later I'll open one of mine up to see what is actually in there.
     
  5. andyr

    andyr Registered User

    So how do you then adjust balance? :confused:

    Regards,

    Andy
     
  6. Lucaslucas

    Lucaslucas just a brand new second hand

    If you want to use the balance you could use a better quality one of same spec

    I bypassed the balance pot on a naim 32 preamp with a suitable resistor and it made quite a significant difference there.
     
  7. andyr

    andyr Registered User

    Then again, with a 32 you're not exactly getting that much in the way of "good sound", to start with!! :p

    Regards,

    Andy
     
  8. Lucaslucas

    Lucaslucas just a brand new second hand

    If you make it linear without the tape loops and phono and add some avondale boards + new vol pot and bypass all the controls then it is good... ;)

    On topic, crappy pots can have pretty drastic effect on the SQ
     
  9. andyr

    andyr Registered User

    I would agree it is better ... but nowhere near "good"! :p

    Any pot degrades the SQ ... some more than others.


    regards,

    Andy
     
  10. istari_knight

    istari_knight pfm Member

    Thanks for the replies everyone.

    Your quite right, that was my error the volume pot is 100K but the rest are 20K.

    I wont be bypassing anything but sourcing higher quality pots is proving rather difficult... alps blue will be fine for volume but the rest ? Gawd knows ! alps RK09 looks close but every one I can find has the wrong shaft/shaft length.

    I'll keep hunting.
     
  11. 337alant

    337alant Negatively Biased

    A couple of years ago my Volume control got very noisy on my Rogers A100 integrated i treated it a couple of times with servisol but it kept getting noisy again within a week or so so i replaced it with a 50K log Alps blue pot, the improvement in sound quality was amazing.
    just recently I started loosing the left channel or it was low this seemed to be associated with the balance control or the speaker selection switch so I stripped it down and i treated the balance, tone and speaker switch with deoxit and again the SQ is back to excellent.
    I have decided that these pots would be very difficult to replace with anything available today and in reality they get very little use compared to the Vol control so they are not likely to be worn out just dried out or tarnished with lack of use so maybe you only need to replace the vol control and just lube the others?
    Alan
     
  12. istari_knight

    istari_knight pfm Member

    Thats beginning to look like my only option Alan.

    I've found some Alps "blue" dual linear that would be perfect for tone/balance but only in either 10K or 30K - I need 20K :(

    There isn't a cheeky way to change the pot resistance using resistors is there ?
     
  13. timhum

    timhum pfm Member

    I suppose you could add a 5K resistor to each end of a 10 K pot. You would have less "span" in the balance control but that might be acceptable.

    There is another way which mimics a log pot. I have a Crown Amcron pre amp which boasts a log/antilog pot as a balance control so it has been done. In your case you could get a dual linear pot and solder a resistor of (I think) one fifth of its value across from the grounded end to the wiper which gives a better "log" law than the log ones off the shelf.

    I am sure that someone will be along in a minute to correct my maths but in principle, as I understand it, a dual 100K pot with two 20K resistors would do the trick.

    Well, you did ask!
     
  14. istari_knight

    istari_knight pfm Member

    Thanks for that food for thought. Its definitely worth a go 'cos those three 99p pots in the signal path cant be helping much surely ? I've checked & there is definitely room for 4 Alps blue's... just!

    I'll have to experiment with some cheap pots & resistors first & see if its acceptable.
     

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