Basic C1 "POP" and noise on all inputs

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by SaturationPt, Oct 3, 2017.

  1. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    967
    Location:
    N.E. Indiana
    Bought this un-tested to pair with my M1A. It crackles, pops, hums, and generally is very noisy with any input.

    It is dead-quiet without input.

    Tuners give it 60hz hum

    Any switch push = pop (including switches on input devices)

    DAC pops when changing modes

    Computer output has a machine buzz

    All of these devices are very quiet, no buzz/hum/pop on other preamps. Using a different preamp with the same M1A amp and the same devices above also is very quiet, ... so the only common component is the C1.

    Is there a coupling or isolating component that seems like a good place to start? I hate to just jump in and re-cap and replace components without identifying the problem first.

    Seems like an open ground, ... but the ground path in this thing is not simple.

    Any thoughts or clues?
     
  2. rjsalvi

    rjsalvi Active Member

    Messages:
    340
    Location:
    San Diego, CA
    Your intuition is good...I'd start with grounds too. More specifically, have you plugged it into a different outlet? ...are there any other ancillary pieces of equipment plugged into its AC outlets (PC, tuner, turntable, etc)? ...have you (gently) wiggled the pots with an input source in place? ... any DC at the outputs? ...have you tried different interconnects between the preamp and power amp? Anyway, it's a place to start.
     
  3. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    967
    Location:
    N.E. Indiana
    Tried all of the swap and eliminate options, same power strip.
     
  4. rjsalvi

    rjsalvi Active Member

    Messages:
    340
    Location:
    San Diego, CA
    Bummer. Well, you know the drill...pop the hood, do a visual on solder joints, whip out the DMM and check continuity on grounds, check components on any board that's common to both channels. It's okay to use foul language...just not around kids. :D
     
  5. Chip Chester

    Chip Chester Super Member

    Messages:
    1,675
    Location:
    Central Ohio
    Pops are often the result of un-tamed DC offsets between stages. Start with the coupling caps.
    Hum could be ground (integrity or architecture), or PSU filtering caps, or poor shielding on interconnect cables...
    "Static" or scratchiness is often dirty pots, or that pesky DC from above being present on the pot wiping surface. Physical cleaning wouldn't help the second type.

    Chip
     
  6. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    967
    Location:
    N.E. Indiana
    Agreed Chip, likely a bad cap passing DC, and probably before the gain pot and selector switch (although could back-feed) mentioned by rj also.

    I'll start chasing it through the schematic later, would like to get this guy working properly again as it's a nice sounding unit.

    Funny thing about me not thinking rogue DC in the signal path:

    When I was a teen, self-taught stereo and electronics junkie, got a job in a local stereo shop as a tech. My first day the owner handed me an amplifier that he couldn't diagnose. I told him it looked like DC in the signal path causing bias problems, showed him how to find the bad coupling cap with a DMM and a scope, he was very happy.

    Now, nearly 40years later I'm possibly missing the same thing that got me that tech job.

    Getting old still beats the alternative though!
     
  7. SaturationPt

    SaturationPt AK Subscriber Subscriber

    Messages:
    967
    Location:
    N.E. Indiana
    There was 1.1vdc on the shield on all inputs, the ground had failed in the trace leading from a connector between boards.

    Thanks to all for the suggestions, and now I will find a suitable place to hook up the C1/M1A and enjoy a glass of wine.
     
    rjsalvi likes this.
  8. rjsalvi

    rjsalvi Active Member

    Messages:
    340
    Location:
    San Diego, CA
  9. Redone90

    Redone90 New Member

    Messages:
    10
    Location:
    Melbourne Australia
    I don't know what the odd's are here, but I also just picked up a Kenwood C1 pre-amp that seems to have exactly the same problem.

    I already had a C2 (pre) with an M2A (power) but, a couple of weeks ago I picked up a C1 with an M2, which unfortunately....I bought untested.:no:

    The C1 definitely has the problem. I tried my working C2 with the M2 and that's fine. Sadly the C1 with either my M2 or M2A has the noise as soon as any input is connected.

    Unfortunately the problem is intermittent and it changes as I use the mouse wheel on laptop, like it's some kind of interference. I've tried using power from a socket that's 20 ft away but the problem continues. Weirdly....while typing this out the noise has stopped and it's working perfectly again:crazy:

    A week ago I opened it up and used Deoxit D5 on the pots but it made no difference.

    If anyone has any idea what the problem could be [and explained simply, to an electrical novice:confused:] I'd be very grateful

    Cheers

    Andrew
     
    Last edited: Oct 23, 2017

Share This Page