Biasing the F5 higher, new trim pots?

lorienblack · 11th February 2014, 08:13 AM

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

ishiru · 11th February 2014, 08:25 AM

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..

Zen Mod · 11th February 2014, 09:04 AM

increase value of resistors which are in parallel with pots

say , for 25-30%

turn pots back before powering up

lorienblack · 11th February 2014, 09:17 AM

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.

ishiru · 11th February 2014, 09:59 AM

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

AudioSan · 11th February 2014, 10:15 AM

the value is not so critical.

KevinHeem · 11th February 2014, 11:57 PM

I couldn't bias my F5 high enough and it was suggested to change R3 and R4 to 4.7K. Works great now.

lorienblack · 12th February 2014, 05:55 AM

Thanks kev! I'll post how it goes when I get around to swapping out the resistors.

11th February 2014, 08:13 AM	#1
lorienblack diyAudio Member Join Date: Sep 2009	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

11th February 2014, 09:04 AM	#3
Zen Mod Official Court Jester diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	increase value of resistors which are in parallel with pots say , for 25-30% turn pots back before powering up __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

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11th February 2014, 08:25 AM	#2
ishiru diyAudio Member Join Date: Oct 2013 Location: Jakarta, ID - Nagasaki, JP	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..

11th February 2014, 09:17 AM	#4
lorienblack diyAudio Member Join Date: Sep 2009	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.

11th February 2014, 09:59 AM	#5
ishiru diyAudio Member Join Date: Oct 2013 Location: Jakarta, ID - Nagasaki, JP	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

11th February 2014, 10:15 AM	#6
AudioSan diyAudio Member Join Date: Feb 2009	the value is not so critical.

11th February 2014, 11:57 PM	#7
KevinHeem diyAudio Member Join Date: Nov 2007 Location: Hudsonville, MI	I couldn't bias my F5 high enough and it was suggested to change R3 and R4 to 4.7K. Works great now.

12th February 2014, 05:55 AM	#8
lorienblack diyAudio Member Join Date: Sep 2009	Thanks kev! I'll post how it goes when I get around to swapping out the resistors.