Supreaux bias question

[Krinor]

I've just built the Supreaux from ROG, and I have to say my search for the ultimate overdrive is at end. This circuit simply shines!
However I have a question for more experienced builders than myself: When I measure for 4,5V at the drain of the jfets, I get values ranging from 9,46 (from a new battery) and down to about 9,36. This looks odd... I touch the negative tip to different ground points, but have so far got the same results all over. Finally I put my DMM aside and biased the thing by ear. I guess this is acceptable. The circuit sounds very, very good, and by playing around with all three trimpots I can tweak it to get anything from a sparkly, beautifull, vintage overdrive to a sputtery, fuzzy distortion. However; I would like to set the pots to the suggested values to get as close to the equivalent tube biasing and the intention of this excellent emulation as possible. How would this be done ?

[dschwartz]

hjmm thats odd...

a fet biased that high should not work at all...
maybe it´s something wromg the way you measured it...but, anyway, trust your ear best!!!!
i allways ear-bias my fets..that 4.5v only puts you in the ballpark

[MikeH]

I tune by ear as well, but I've found you can't just tune to the loudest point on each fet.  Sometimes this makes the thing sound really muddy and oversaturated to my ears.  The first couple stages I generally tune to the loudest point, but then I adjust subsequent ones to the amount of "tone" or "sparkle" that I like.  This of course is not true for all circuits, and probably of no help to you.  You're welcome!

[Krinor]

Thanks for your input guys.

Mike, actually that's just the same approach I went for myself. I guess I did it by instinct. The first fet gives me a nice entrance volume, and the next two stages I have tweaked to my liking. And they are not at the "top" position as you warn against. I rolled them back a fair bit to avoid that over the top muddy sputter which resides around the max position.

...And then I boxed it up and played along with Jimmy the whole afternoon. What a great sound!

Professor Tweed is next!

[Ardric]

Is your meter a high input impedence DMM?  The old analog meters usually have a pretty low input impedence, and on this kind of circuit that won't work.