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    SP12 Right & Left Gain Controls

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    guentherj2

    Posts : 50
    Join date : 2013-06-22
    Location : Bellingham, WA

    SP12 Right & Left Gain Controls

    Post by guentherj2 on Fri Feb 06, 2015 10:21 pm

    I've had this SP12 for a year or so. I had to replace the stepped volume pot because it stopped working properly. I replaced it with a Blue Velvet and have been very happy with it.

    Now the right and left stepped gain controls are giving me problems - cutting out and making scratchy noise.

    Does anyone know the specs for replacing these pots or suggestions for what to replace them with?

    Thanks

    John.

    Elrick

    Posts : 71
    Join date : 2012-09-02
    Location : Bellingham WA

    Re: SP12 Right & Left Gain Controls

    Post by Elrick on Sat Feb 07, 2015 7:19 pm

    Good question. I never really understood the rationale for the separate gain controls over simply using the balance pot. But I imagine they are fun to play with. I would think you could measure the resistance change as you rotated the gain knob to get an idea of the range, then replace with two more alps pots of similar value. Perhaps there is more to it than that. Be interesting to hear what others think.

    guentherj2

    Posts : 50
    Join date : 2013-06-22
    Location : Bellingham, WA

    Re: SP12 Right & Left Gain Controls

    Post by guentherj2 on Sat Feb 07, 2015 11:10 pm

    It would be interesting to hear what others think - kind of why I posted on this forum. I'd like to start with knowing the values of the pots that are in it - not provided in the paperwork that came with the preamp as far as I can tell. I do like having control over the separate gains - would be nice to have better pots in there to do it with however. Maybe I'll end up having to measure the resistances to determine what I have?

    flak monkey

    Posts : 37
    Join date : 2015-02-01
    Location : Norfolk, UK

    Re: SP12 Right & Left Gain Controls

    Post by flak monkey on Tue Feb 10, 2015 6:50 am

    I'd be interested too. Not sure whether to fit gain controls or not to my SP12 as I haven't started building it yet. I can't remember the last time I ever used similar controls on my previous kit, infact for the last 10+ years my amps haven't had anything but volume and input selectors on them. So I am toying with the idea of not fitting any at all.

    guentherj2

    Posts : 50
    Join date : 2013-06-22
    Location : Bellingham, WA

    Re: SP12 Right & Left Gain Controls

    Post by guentherj2 on Tue Feb 10, 2015 11:36 pm

    They certainly are not necessary but water under the bridge - that ship has sailed for me. I do like having them when they work!!! I like keeping my normal listening volume at high noon and adjusting the right and left gains depending on the source. I also would not get one with the dozens of resistors on the volume pot like I got in mine.

    If you end up getting the separate R/L gain controls and can figure out what they are rated - please do check back and let me know.

    Thanks flak monkey.

    peterh

    Posts : 679
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: SP12 Right & Left Gain Controls

    Post by peterh on Wed Feb 11, 2015 3:21 am

    brAun did a simular thing with their amps ( CSV 1000 et.al) , they had a "balance control" made up
    by 2 concentric pots connected in the same direction, thus if turned together they would
    act exactly like an volume pot. But as they were connected earlier in the amp they made the same
    function as the volume - with one exception : the volume control had a  "loudness" tap, the
    combination made it adaptable where ( if any) loudness one wanted. If i had the volume
    fully clockwise and used the "balance" as volume there was no loudness.

    Have a peek at the brAun design, it was ( is) still a very good one!  They had 2 tube amps;
    csv13 ( el84 style ) and csv60 ( using 4 el504 30w/channel)

    http://www.and-up.net/stock/braun/Braun-CSV60.htm
    http://www.mcamafia.de/tubes/braun/intro.htm



    Last edited by peterh on Wed Feb 11, 2015 10:33 am; edited 1 time in total (Reason for editing : adding links to the amp)

    TMadden

    Posts : 99
    Join date : 2011-12-22

    Re: SP12 Right & Left Gain Controls

    Post by TMadden on Wed Feb 11, 2015 10:21 am

    guentherj2 wrote:They certainly are not necessary but water under the bridge - that ship has sailed for me. I do like having them when they work!!! I like keeping my normal listening volume at high noon and adjusting the right and left gains depending on the source. I also would not get one with the dozens of resistors on the volume pot like I got in mine.

    If you end up getting the separate R/L gain controls and can figure out what they are rated - please do check back and let me know.

    Thanks flak monkey.



    The left and right gain controls are typically 120K, made with 12 10K resistors. Have you tried a bit of contact cleaner like DeoxIT on the contacts?

    tubes4hifi
    Admin

    Posts : 1292
    Join date : 2008-11-30

    Re: SP12 Right & Left Gain Controls

    Post by tubes4hifi on Wed Feb 11, 2015 1:05 pm

    Hi John,
    you probably have the old style attenuators made with cheap rotary switches.
    The ones we supply now are high quality 21 step attenuators, email me and I can get you a new pair, or a pair of standard volume controls, your choice.
    Roy info@tubes4hifi.com

    guentherj2

    Posts : 50
    Join date : 2013-06-22
    Location : Bellingham, WA

    Re: SP12 Right & Left Gain Controls

    Post by guentherj2 on Wed Feb 11, 2015 4:12 pm

    Thanks for posting Roy. Yes, I think you mentioned upgrading these pots when I had to replace my volume pot. I'll shoot you an email.

    And thanks all for the feedback. I guess patience is a virtue on this forum.

    John

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