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    SCA 35 Output Transformer

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    jwb474

    Posts : 8
    Join date : 2014-07-13

    SCA 35 Output Transformer

    Post by jwb474 on Sun Mar 15, 2015 11:34 am

    I am starting to move forward on my SCA 35 project and wanted to changed the output transformers in order to go from 8 and 16 ohm to 4 and 8 ohm. My question is this: Is the feedback resistor and capacitor which was optimized for the 16 ohm output level and impedance of the original transformer OK for the new transformer? I had sent a request to Dynakitparts.com a few weeks back, but have not got a response.

    peterh

    Posts : 643
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: SCA 35 Output Transformer

    Post by peterh on Sun Mar 15, 2015 11:46 am

    jwb474 wrote:I am starting to move forward on my SCA 35 project and wanted to changed the output transformers in order to go from 8 and 16 ohm to 4 and 8 ohm. My question is this: Is the feedback resistor and capacitor which was optimized for the 16 ohm output level and impedance of the original transformer OK for the new transformer? I had sent a request to Dynakitparts.com a few weeks back, but have not got a response.
    You refer to R37 ( 82k ) ? Try 47k. The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.

    jwb474

    Posts : 8
    Join date : 2014-07-13

    Re: SCA 35 Output Transformer

    Post by jwb474 on Sun Mar 15, 2015 11:55 am

    You refer to R37 ( 82k ) ?  Try 47k.   The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.[/quote]

    Yes. 47K does make sense since the max voltage is 1/2 of what it was. I do have the equipment to test the amp. On a related note, has anyone here used Virtins Technology's multi-instrument software? I am trying it out and it appears to be great for a hobbyist.

    jwb474

    Posts : 8
    Join date : 2014-07-13

    Re: SCA 35 Output Transformer

    Post by jwb474 on Sun Mar 15, 2015 11:57 am

    jwb474 wrote:You refer to R37 ( 82k ) ?  Try 47k.   The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.

    Yes. 47K does make sense since the max voltage is 1/2 of what it was. I do have the equipment to test the amp. On a related note, has anyone here used Virtins Technology's multi-instrument software? I am trying it out and it appears to be great for a hobbyist.[/quote]

    peterh

    Posts : 643
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: SCA 35 Output Transformer

    Post by peterh on Sun Mar 15, 2015 1:30 pm

    jwb474 wrote:
    jwb474 wrote:You refer to R37 ( 82k ) ?  Try 47k.   The cap C21 you need a scope and make it as big as
    preventing overshoot when feeded with squarevawes. 12 pF could be a good starting point.

    Yes. 47K does make sense since the max voltage is 1/2 of what it was. I do have the equipment to test the amp. On a related note, has anyone here used Virtins Technology's multi-instrument software? I am trying it out and it appears to be great for a hobbyist.
    [/quote]
    It's more 1/sqrt(2) Thus 47 - 56 k is what you need as R37

    rmyauck

    Posts : 9
    Join date : 2012-02-18

    Re: SCA 35 Output Transformer

    Post by rmyauck on Wed Mar 18, 2015 1:56 pm

    If it were me I would keep the vintage OPT's due to their well regarded sonics and try them with your speakers on the different taps with no regard to worrying about them not being matched. I think you will be pleasantly surprised!

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