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


    Pas Hum/Buzz

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    rudes

    Posts : 44
    Join date : 2012-03-07

    Pas Hum/Buzz Empty Pas Hum/Buzz

    Post by rudes on Tue May 12, 2020 12:25 pm

    I know this is something that I'm sure has come up before! I have a Pas that I got on the bay. It was incomplete. I just installed the Erhard Audio PS board. I've used this board before without any problems. The selector switch it came with had been changed along with the Phono board. I'm trying to find where this hum/buzz is coming from! All voltages are good. Inputs grounds are good. Single ground wire going to each board from PS board. PS board and red/yellow trans wire is grounded to chassis. I tried shorting points 1, 2 and 9 on PC5. The noise remained. On pin 4 I should have less than 1 volt, I have 9 on both tubes. Would appreciate any input!
    peterh
    peterh

    Posts : 1317
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Pas Hum/Buzz Empty Re: Pas Hum/Buzz

    Post by peterh on Mon May 18, 2020 1:55 pm

    rudes wrote:I know this is something that I'm sure has come up before! I have a Pas that I got on the bay. It was incomplete. I just installed the Erhard Audio PS board. I've used this board before without any problems. The selector switch it came with had been changed along with the Phono board. I'm trying to find where this hum/buzz is coming from! All voltages are good. Inputs grounds are good. Single ground wire going to each board from PS board. PS board and red/yellow trans wire is grounded to chassis. I tried shorting points 1, 2 and 9 on PC5. The noise remained. On pin 4 I should have less than 1 volt, I have 9 on both tubes. Would appreciate any input!

    Some measurments on a pair of  dynacoPAS:
    selecting phono, with inputs shorted and volume fully up will typically have 2.7mV rms at each channel. Noise dominating hum not visibel on scope. All tonecontrols in middle balance centered.

    With volume at zero ( which also is high level input with shorted input) the total
    output is app. 700uV

    This is measured on 2 pas3x  both using triodes powerboard, one with 12x4 the other
    with 2 un4007 rectifiers.

    All done with all covers mounted.


    Last edited by peterh on Mon May 18, 2020 1:56 pm; edited 1 time in total (Reason for editing : spelling)

      Current date/time is Mon May 25, 2020 9:22 pm