The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    SP14 Output Capacitor Values

    Share

    AudioMartin

    Posts : 4
    Join date : 2014-06-29

    SP14 Output Capacitor Values

    Post by AudioMartin on Tue Jul 29, 2014 12:51 pm

    Hi there,

    I'm curious to know if anyone has experimented with 0.22 uF vs 0.33 uF capacitors in the C3/C3a position of an SP14 preamp.  The reason I ask is that my parts list calls for 0.22 uF, but all photos I see on the internet show 0.33 uF caps there.   My understanding (I'm slowly learning circuits) is that this capacitor, among other things, affects the LF rolloff point.

    Cheers,
    Martin

    GP49

    Posts : 733
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: SP14 Output Capacitor Values

    Post by GP49 on Thu Jul 31, 2014 3:03 pm

    0.33µF will give a slightly lower bass roll-off point.  The difference should not be significant.

    The exact frequencies depend on the impedance of the load.  Into a 100KΩ load, often seen in
    tube equipment, the -3dB rolloff point of 0.22µF is approximately 7 Hz; of 0.33µF, approximately
    5 Hz.

    SOME amp stages limit output bandwidth to keep them from getting into trouble at low bass
    frequencies.  A well-designed one will not have to rely on the difference between 0.22µF
    and 0.33µF!

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: SP14 Output Capacitor Values

    Post by tubes4hifi on Sat Aug 02, 2014 6:46 pm

    perfect reply, thanks GP49

    AudioMartin

    Posts : 4
    Join date : 2014-06-29

    Re: SP14 Output Capacitor Values

    Post by AudioMartin on Sun Aug 03, 2014 8:34 pm

    Wonderful, thanks for the reply.

    All makes sense.

    Following this, I looked up the math. 100k is the right value for impedence, and I don't much care if the rolloff is 5Hz or 7Hz. Turns out a friend has some Mudorf Silver/Gold Oil caps he can lend me. Also found some 0.22 uF Russian Teflon caps. Should be interesting.

    Cheers,
    Martin

    Sponsored content

    Re: SP14 Output Capacitor Values

    Post by Sponsored content Today at 2:37 pm


      Current date/time is Mon Dec 05, 2016 2:37 pm