Mongoose / Giant Hogweed queries.

Posted by Beaker on Nov 01, 2015; 1:46pm
URL: http://guitar-fx-layouts.238.s1.nabble.com/Mongoose-Giant-Hogweed-queries-tp25642.html

By pure coincidence, I was in the middle of building a Roger Mayer Mongoose, when Alex posted the Giant Hogweed layout up on the main page. I want to build the Hogweed, but I want to get the Mongoose right first.

Reading David Rolo's notes on the Hogweed, he says that it is important to get the bias right on the LM308N to get the best sound out of the Mongoose circuit, with the optimum bias voltage at 5.5V.
So I measured my voltages, and found that I was only getting 4.2V on the IC.

Looking at the schematic:



and the layout:



I changed R5 (47K) - the left hand one on the layout, to a 33K which got my voltage up to 5.8V, and yes it sounds much better.
So then I changed R4 (47K) - the right hand one on the layout to a 33K to match.

Have I done this right? Do I need to change both of them or not?

David's Hogweed schematic has both 47K resistors on as well, so do they need altering too to get 5.5V?

Help, I'm getting confused!!!