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    Input regulation pot?

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    Greg_M

    Posts : 40
    Join date : 2010-09-18
    Location : Poulsbo, WA

    Input regulation pot?

    Post by Greg_M on Thu Jun 09, 2011 10:06 am

    As mentioned in another thread, I plane to use my ST70 in a Leslie speaker. The output from the organ is a little high (up to 2v) so I was thinking I could put a pot on the input and regulate how much signal the ST70 is getting. A lot of preamps use 100k pots as a volume control and I was wondering if that would work?
    Anybody have a suggestion for the pot value?
    How about wattage?

    Thanks for looking.

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Input regulation pot?

    Post by j4570 on Thu Jun 09, 2011 11:06 am

    I have one of the stepped attentuator kits s Bob sells and have been using my newly rebuilt ST70 without a preamp. I imagine it would work well in your case. See here:

    http://www.tubes4hifi.com/ST70.htm

    About 1/2 way down. In the full clockwise position, it's a straight pass through.

    The only downside is that it takes the place of the stereo/mono switch, and if it's a stock ST 70, that would need to be removed and bypassed, and I don't know if there is enough room, I put mine in with the rebuild and a VTA board. I'm not sure if you are using the amp mono or stereo for the Leslie (I think Stereo based on your previous discussion). Also, you could probably mount it remotely in a seperate box and use RCA connectors.

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Input regulation pot?

    Post by j4570 on Thu Jun 09, 2011 11:12 am

    Here is a kit that would allow adjusting the coarse for both channels at the same time, and each channel individually some in fine increments:

    http://glass-ware.stores.yahoo.net/baat.html

    No idea of how well it works. Might be better if you are running one channel basss and one treble to do some matching.


    mantha3

    Posts : 298
    Join date : 2010-11-10

    Re: Input regulation pot?

    Post by mantha3 on Thu Jun 09, 2011 11:39 am

    X 2 on the stepped attentuator kits s Bob sells. A nice little attenuator... 100K. I think it would add value to the amp should you want to sell it. Looks nice with the nice black knob on the front of the amp.


    Greg_M

    Posts : 40
    Join date : 2010-09-18
    Location : Poulsbo, WA

    Re: Input regulation pot?

    Post by Greg_M on Thu Jun 09, 2011 11:53 am

    I really didn't want to modify the amp as it is my intension to put a real Leslie amp back in when I can find one. The ST70 is way to nice of an amp for this LoFi application. It's just a temporary use and I just wanted to protect the amp from overload

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Input regulation pot?

    Post by j4570 on Thu Jun 09, 2011 1:26 pm

    How about building a fixed attentuator circuit then? Cheap and would provide what you need I think.

    Greg_M

    Posts : 40
    Join date : 2010-09-18
    Location : Poulsbo, WA

    Re: Input regulation pot?

    Post by Greg_M on Thu Jun 09, 2011 3:43 pm

    Sure.
    What would that look like?

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Input regulation pot?

    Post by j4570 on Thu Jun 09, 2011 3:53 pm

    Start here:

    http://en.wikipedia.org/wiki/Potentiometer

    You would use two or more resistors to mimic a fixed position on the pot.

    Greg_M

    Posts : 40
    Join date : 2010-09-18
    Location : Poulsbo, WA

    Re: Input regulation pot?

    Post by Greg_M on Thu Jun 09, 2011 4:00 pm

    Why not just use something like a 10k bias pot?

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Input regulation pot?

    Post by j4570 on Thu Jun 09, 2011 5:35 pm

    A pot is fine too. Sometimes people don't want things to be adjusted or to spend the Money for a pot.
    It was just a suggestion. I would probably use a pot too

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