Tuesday, 5 August 2014

McGillwell FET Booster

Since we're posting tiny circuits today, i thought i'd post a recently traced booster. No input cap, no power filtering or any other modern day trinkets. Tiny booster with outside the box thinking in design. Thanks for trace to Bernardduur at FSB.


11 comments:

  1. Sound 1, 2 and 3 - is this a tone control?

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    Replies
    1. No. It's the "Sound" control. Boosting bassier to CCW, near unity at center and boosting trebly at CW. Or so i've heard.
      +m

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    2. I built this on my breadboard today with a J201 - works as advertised but not much boost there with my circuit. The "sound control does "boost" at the far excursions either direction, with a noticeable loss of volume in the middle. There is gain, but pretty gritty and not much sustain. of course, with the BF245B it could be completely different.

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    3. If you still have it on your breadboard, you could try to swap that 47k from supply to drain with a 100k trimmer and see if you can bias the J201 correctly. Your low output symptoms may simply be caused by misbiased J201.
      +m

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    4. Thanks - wish I had known that trick. I might try it again, but I did tear it down already. Biasing fets is still new territory to me.

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    5. This comment has been removed by the author.

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    6. sorry - wanted to edit
      to +M... above you say to swap out the 47 from supply to drain with a 100k trim. Can you be more specific on which of the three 47k resistors that is (there isn't one going from supply to drain). I assume it drain to gnd? what +v do I want?

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    7. there is only 1 resistor going to the drain, the 47k from +9v (supply) not ground

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    8. That is weird, I though I replied to this but I don't see it. My brain mixed up "supply" (as in 9v) with "source" (as in DSG). That's how we learn.

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  2. I see - cool, I will have to try this out. I love the Brian May boost - very similar but no 'sound" control there.

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