Accuphase E-202 Clipping when bass boost

Discussion in 'Solid State' started by seowsheng, Jan 30, 2018.

  1. seowsheng

    seowsheng New Member

    I recently revived an old Accuphase E-202, but when I turn on the bass boost, I can hear slight clipping.

    I have not re-cap the unit, only work done is replacement all the failing and ailing transistors on the power supply board (719-0004-00), main drive amp board (710-0002-00) and the equalizer board (711-0002-10).

    Only failing transistors were replaced with the following replacements:

    1) 2SC1451 replaced with KSC3503 on the power supply board and main amp board
    2) 2SC1746 replaced with KSC1815 on the power supply board
    3) 2SA620 replaced with 2N2907A on the main amp board
    4) 2SA856 replaced with 2N2907A on the equalizer board and power supply board
    5) Output power transistors replaced with MJ21193-PNP and MJ21194-NPN
    5) All the 4 main capacitor changed to Nichicon KG 1000uf 63V

    Listening at low volume, up-to 10 o'clock volume without bass boost, every works great. At high volume or with bass boost, I can hear clipping.

    When the COMP button is depressed, (bass boost), I can hear slight clipping.

    The test I have done is separate the amp and pre-amp and run it with a Marantz 1070.

    In both test, when E-202 is acting as pre-amp and Marantz 1070 as power amp, I can hear the clipping at volume around 11 o'clock.

    When running E-202 as power amp and Marantz 1070 as pre-amp, I can hear clipping when running full bass on the Marantz amp.

    What is causing the clipping?

    Do I really need to re-cap all the electrolytic cap



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  2. Grenadeslio

    Grenadeslio Super Member

    "What is causing the clipping?"

    Too much bass.
  3. mbz

    mbz Super Member

    Melbourne, Victoria
    A better approach might be to use an oscilloscope and signal generator (sine and square waves) to track down this problem.
    PC SW versions that use the PC's sound card are available online. I'm sure that you hear some distortion and you think that
    it's due to clipping, probably right, but Id like to see the trace.
  4. seowsheng

    seowsheng New Member

    Thanks guys, will have to put this aside for now.
  5. inductor

    inductor Super Member

    fets in the tone cct give problems
  6. seowsheng

    seowsheng New Member

    Finally, get around to sit down and re-cap the power supply board.
    Hooray! No more clipping like sound. It appears re-cap the power supply board resolve the power starvation issue.
    Now the bass sing sweetly.


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  7. ants2au

    ants2au Ants

    Sydney, Australia
    q re the output transistors, did you have to match the pairs? as each channel has parallel PNP and NPNs. NOTE: I am not referring to matching npn with pnp..
    I was planning on doing the same...
  8. seowsheng

    seowsheng New Member

    @ants2au I didn't have to match the pairs.

    On another note, I have also replaced the tantalum capacitors (C3, C4, C5 and C6) on the equalizer board, 711-0002-10, huge improvement. Now the bass is tamed and treble sounds the way it should be.

    I also notice replacing tantalum with an electrolytic cap is not recommended. Always replace a tantalum with another tantalum. Not sure why there are some many threads out there that advise people to replace tantalum with an electrolytic cap.
    ants2au likes this.

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