Super PAS Three caps to isolate DC in output

Discussion in 'Audio by Van Alstine' started by daveshel, Apr 12, 2016.

  1. daveshel

    daveshel Active Member

    Tucson AZ
    It's my understanding that some tube gear needs to have some caps between the preamp and the amp in case there's any DC in the preamp's output.

    (I'm experiencing some strange farting and popping sounds for the first few minutes of operatiion of my Super PAS Three with my mostly stock Mark-III monoblocks and I'm wondering if this is what I'm experiencing.)

    What are the symptoms of this issue. I've hears that if I put a 1mfd electrolytic on the output this will isolate the DC, but I'd like to verify the value - along with the polarity of the electrolytic.


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  2. avahifi

    avahifi AK Member

    Woodbury, Minnesota
    The Super Pas Three already has AC coupled outputs, as do almost all vacuum tube preamplifiers. To help you out, send me an e-mail requesting the complete Super Pas Three rebuild kit manual, which is complete with build notes, diagrams, photos, step by step instructions, and the complete schematic and parts list. We will supply this at no charge as a .pdf file.

    Your noise issue is most likely a defective tube. Try swapping the two line tubes from channel to channel and see if the issue changes channels to confirm this.

    The output coupling capacitors are 3.3µF 100V film type (not polarized).

    Your are welcome to call me at 651-330-9871 for more help, but not before next Monday.

    Frank Van Alstine

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