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Thread: Bell BF-20 stereo flanger setup

  1. #1
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    Bell BF-20 stereo flanger setup

    I have two 70s flangers in for repair and need the setup procedure for the trim pots. They're both Mk II rackmount units. The modulation is very offset and peaky. Plus, the feedback control causes oscillation and the channels are considerably different in how the controls respond, depending whether Manual, Envelope or Oscillator modulation is selected. An experimental tweak tells me that there's a lot of interaction and it's unlikely that random adjustment will give good results.

    Also, does anyone have schematics for this model?

    EDIT: that should be BEL, not BELL.

  2. #2
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    This is the MkIII. It may or may not help you..


    Bel.zip
    Experience is something you get, just after you really needed it.

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    Thanks. The MkIII is a lot different, though maybe some of the building blocks are similar enough to infer what some of the adjustments may do in the MkII. Annoyingly, the identification has been removed from the main ICs. I think I have my work cut out.

  4. #4
    I'm a member? nickb's Avatar
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    I'd definitely call them up and ask. You've nothing to lose. Even if it's just the adjustment procedure.
    Experience is something you get, just after you really needed it.

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    Gave them a try - emailed to two different addresses but no reply. Also rang and just get "Your call cannot be answered, please leave a message" But no calls back.

    I've pretty much figured out how to set them up, but one has two of the 14-pin ICs that need replacing. I have a strong feeling they're just 4000 series CMOS, but have not been able to figure out what they are just yet. I was expecting one to be a 4013 because it drives the SAD1024 delay chip and this is the usual setup, but not so in this. The other device is probably the clock source.

    This is where one of those IC analysers would be useful - just plug in one of the good mystery chips and it identifies it from a device library.

    If anyone knows what those ICs are it would save a whole load of time.

  6. #6
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    I got a reply to one of my E-mails and have made a little progress - at least they've asked for some pics of the board and IC location. Hopefully something will materialise.
    nickb likes this.

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