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A guide to building the Pass F4 amplifier.
A guide to building the Pass F4 amplifier.
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Old 25th March 2020, 05:08 PM   #1711
66deg is offline 66deg  United Kingdom
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Thanks Dennis.
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Old 25th March 2020, 05:46 PM   #1712
Dennis Hui is online now Dennis Hui  Canada
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A guide to building the Pass F4 amplifier.
I had a closer look and it seems you have 22.1K for R8? If so, I suggest
changing that to 27.4K (as in the latest schematics) and leave R9 at 10K.
If you change R9 to 4.75K then even with max value of P1, you will have significant
current flow (since you already have 110mV across 0.47 in your current setup).

Sorry for the confusion.
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Old 25th March 2020, 05:57 PM   #1713
66deg is offline 66deg  United Kingdom
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No problem, would this be the correct one?CMF6027K400FKEK Vishay / Dale | Mouser France

One other Quick question regarding max value on the Bourns pot, it seems to turn endlessly should I just do say 10 clockwise turns to be sure it is at max value?

Last edited by 66deg; 25th March 2020 at 06:01 PM.
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Old 25th March 2020, 06:21 PM   #1714
Dennis Hui is online now Dennis Hui  Canada
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A guide to building the Pass F4 amplifier.
That works.

Or the RN60 version (in case you want all your resistors to look the same ):

RN60D27R4FRE6 Vishay / Dale | Mouser Canada

You should hear a slight click when you are at the end of the pot's adjustment range.
But that doesn't tell you whether you're at max or min value.

In your case you know that you run out of adjustment room for bias. That occurs
when P1 is at min value. So turn in the opposite direction so that the bias
decreases and when you hear the click, you should then be at maximal value.
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Old 25th March 2020, 07:25 PM   #1715
66deg is offline 66deg  United Kingdom
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If I have understood the max value of the Bourns pot equals minimum bias which is where I should be before next switch on?

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Old 25th March 2020, 07:57 PM   #1716
Zen Mod is offline Zen Mod  Serbia
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A guide to building the Pass F4 amplifier.
exactly , max across trimpot will give min Iq
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Old 25th March 2020, 08:01 PM   #1717
Dennis Hui is online now Dennis Hui  Canada
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A guide to building the Pass F4 amplifier.
What ZM said.
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