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Hoffman Amps Forum image Author Topic: Calculating variable NFB resistance on 5F1 champ with an 8 ohm OT.  (Read 1992 times)

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Offline xochipelli

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  I'm trying to wrap my head around a variable NFB on a fender 5F1 champ using a Mercury Magnetics 8 ohm OT.
  Now the Champ with a 4 ohm output uses a 22K NFB resistor so i'm guestimating that maybe  a 60ish K for an 8 ohm output?
Since this will be on a pot am i on the right track considering a 100K linear pot with a 10K resistor?
Ideally i would like the sweet spot located somewhere's near the 12 o'clock position on the NFB pot and not have the min/max positions to be unusable/sound like crap.
Any help would be appreciated - thx!

Offline sluckey

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Re: Calculating variable NFB resistance on 5F1 champ with an 8 ohm OT.
« Reply #1 on: March 25, 2024, 07:13:04 am »
Just experiment. A 100K linear pot with a 10K resistor sounds like a good starting point. Set the pot to 12 o'clock and experiment with the 10K, changing its value up/down until you find your sweet spot.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

 


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