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Thread: Croft preamp whistling.

  1. #1
    Join Date: May 2011

    Location: Sheffield

    Posts: 225
    I'm John.

    Default Croft preamp whistling.

    Hi All,
    I have a croft micro, upgraded by Glenn a couple of years ago to 25r spec. Over the weekend it's started to make a loud whistling sound through the speakers. It's present on both line and Phono inputs, and is insensitive to volume control position even when set to "zero". It does, however go away when the "mute" switch is engaged. Initially suspected a microphonic line stage valve, but replacing this didn't help. Anyone have any ideas?
    Cheers
    John

  2. #2
    Join Date: Dec 2015

    Location: Alicante. Spain.

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    I'm Adrian.

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    Is it on one channel or both? Have you swapped out all valves?
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  3. #3
    Join Date: Oct 2012

    Location: NE England

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    I'm Jez.

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    Probably a power supply regulator issue. Not a user serviceable problem I'm afraid.
    Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)

    Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
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  4. #4
    Join Date: May 2011

    Location: Sheffield

    Posts: 225
    I'm John.

    Default

    Quote Originally Posted by farflungstar View Post
    Is it on one channel or both? Have you swapped out all valves?
    On both channels. As it's present when the line input is selected I'd assumed (perhaps incorrectly?) that the phono stage valves couldn't be the problem.

  5. #5
    Join Date: May 2011

    Location: Sheffield

    Posts: 225
    I'm John.

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    Any good amp fixers in Sheffield? (Or maybe I should send it to Mr Croft).

  6. #6
    Audio Al is offline Pishanto Specialist & Super-Daftee
    Join Date: May 2012

    Location: Dagenham Essex

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    I'm Allen.

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    Quote Originally Posted by fiddlemaker View Post
    Any good amp fixers in Sheffield? (Or maybe I should send it to Mr Croft).
    This
    [

  7. #7
    Join Date: May 2011

    Location: Sheffield

    Posts: 225
    I'm John.

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    Quote Originally Posted by Audio Al View Post
    This
    Cricket season, though.

  8. #8
    Audio Al is offline Pishanto Specialist & Super-Daftee
    Join Date: May 2012

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    I'm Allen.

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    Or Alan ( Firebottle )

    or Ampregen http://www.ampregen.com

    I have used Graeme he rebuilt my AI500
    [

  9. #9
    Join Date: Feb 2013

    Location: W Lothian

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    I'm Grant.

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    Yes sounds power related
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  10. #10
    Join Date: Apr 2011

    Location: Dublin

    Posts: 232
    I'm Simon.

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    I'd email Glenn, he is normally pretty good at replying. He confirmed a suspected transformer fault on my micro 25 and offered to repair or supply a replacement if I was happy with a soldering iron.

    So 15 minutes with the iron and pre amp back running perfectly.

    Sent from my SM-G930F using Tapatalk
    Source: Thorens TD124 Rega RB300, Sumiko bluepoint No2., Cambridge Audio D500 Special Edition CDP, Squeeze box Touch, PC with Trends Audio USB Audio DAC UD-10 Amplification: Croft Micro 25 basic pre, Leak Stereo 20, Trends Audio Class T TA-10, Fisher X100-A Speakers:Impulse H6 Interconnects: Handmade silver and TNT audio CAT5 speaker cables

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