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Old 11th February 2014, 09:13 AM   #1
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Default Biasing the F5 higher, new trim pots?

I made some resistor changes, recommended by NP, to "warm up" the F"5. It worked very well and I'm happy, but the amp runs a lot cooler.

I have it biased at .59v but that's got the trim pots maxed out, I want to be able to up the bias until the amp runs at a better temp.

I picked up some pots (10k), thinking they were Bourne ones, but found they were copies. Is the quality of the pots essential to the SQ? Or is their function simply to shunt power rather than deal with the signal itself?

Thanks for any suggestions
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Old 11th February 2014, 09:25 AM   #2
ishiru is offline ishiru  Indonesia
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could you post the bias circuit here?..i might can help but after searching the F5 schemes i'm confused where's the bias

and bias pots didnt affect the SQ imo.but they affect the stability of the bias which could affect the SQ..
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Old 11th February 2014, 10:04 AM   #3
Zen Mod is offline Zen Mod  Serbia
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increase value of resistors which are in parallel with pots

say , for 25-30%

turn pots back before powering up
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Old 11th February 2014, 10:17 AM   #4
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Thanks guys - I had considered upping the value of the resistors in parallel, but I would have been making a shot in the dark re values.
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Old 11th February 2014, 10:59 AM   #5
ishiru is offline ishiru  Indonesia
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use LTSpice..draw the schematic and adjust the bias resistors there.you could find how much resistance did you need safely instead of take the value blindly
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Old 11th February 2014, 11:15 AM   #6
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the value is not so critical.
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Old 12th February 2014, 12:57 AM   #7
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I couldn't bias my F5 high enough and it was suggested to change R3 and R4 to 4.7K. Works great now.
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Old 12th February 2014, 06:55 AM   #8
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Thanks kev! I'll post how it goes when I get around to swapping out the resistors.
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