Fatpants trimpot

[gtg975n]

Would someone with experience building a FatPants give their advice on how they set the 50k trimpot (T1)?  I have mine currently set by ear to where the volume was the loudest.  This wasn't all the way in one direction at a max or a min value, but about a third of the way in the clockwise direction.  Is there a more quantitative way of setting it (i.e. measuring the drain voltage of the transistor)?  Thanks!

[bigmufffuzzwizz]

The pdf for the fatpants says "17k is the default setting for T1. Adjust the trimpot for the hottest output you desire." If you wanted to use it at default setting mesaure the trimpot (with an ohmmeter) until it's at 17K ohms. And if you want more output from there, increase.

[madbean]

The way you went about it is the easiest for fine tuning by ear. Set the fat control at max and then dial in the trimmer to where it sounds best to you. You can, of course, go by the 17k setting, too.

[jfk1063]

Hi,
I have mine set by ear (the loudest), but when I measured the bias it is 3v instead of being between 12v and 14v. When set at 12v it's softer and 'dull'.
Any thoughts?
Thanks!

[midwayfair]

Hi,
I have mine set by ear (the loudest), but when I measured the bias it is 3v instead of being between 12v and 14v. When set at 12v it's softer and 'dull'.
Any thoughts?
Thanks!

This is normal. FETs tend to get louder and louder as you decrease the voltage at the drain until you get near the cutoff point, and then they shut off. Biasing it so low is decreasing the headroom, however. Increasing the gain will, as you say, make it less "dull" sounding, but that's mainly because you're introducing upper harmonics through some distortion. The Fatpants should have a slightly dulled top end -- this is kinda part of the midrange-y sound, and this also helps manage the harmonics created when pushing a tube amp with it.

[hammerheadmusicman]

I think i biased mine at 9v, for the best.

[jfk1063]

Thank you for the response and information.
I will bias again and play some more with it.
Cheers from Amsterdam!