I had the Bearfoot version of the HBOD and posted up some shots over on FSB. Another member there did a tracing and reported a couple of differences to the Yellow Shark schematic. I dug back through most of the old HBOD threads and noticed a couple of differences between an early working/rough draft schematic and the final one that madbean posted. Anyway, I just got a new fabbed Yellow Shark board this week and wanted to see if it could match the Bearfoot version I had. Here are the changes I put in:
R9 = 150k
C4 = 22uF
C5 = 220n with 4k7 resistor in series
Q1 = Fairchild BF244A (on order - using 2n5457 now)
I don't think the different JFET for Q1 will have a material impact on the sound. The R9 change also didn't seem to change anything. C4 at 22uF shaved off some top end and definitely made it more like the Bearfoot.
Put the 4k7 resistor in between C5 and lug 3 of the nature control (cut the trace and wire the resistor between instead).
Anyway, to my ears these changes did the trick so this new build sounds just like the Bearfoot HBOD I had. But even with the current schematic the sound of a clone to the original is 99% (as long as you use a larger cap at C5). I just wanted to see if I could get that extra 1%.
That's very interesting because C4 was originally listed as 22uF on the HoneyBee by the original tracer, and then corrected to 2u2 later on, IIRC. I have built it with a 22uF there and definitely did not like it (too much bass).
An alternate way to do the 4k7 @ C5 would be two wire lugs 3&1 from the board to the pot and put the 4k7 between lugs 2&1. This is slightly different but it would get you close to the same results.
Thanks for sharing your feedback!
I agree that it sounds better with the 2u2 because I preferred my original clone over the Bearfoot when I did the comparison. ;D But stil, I wanted to find out why there was an audible difference between the two.
What does adding the 4.7K resistor do?
Found a nice mod that can let you dial in a little more top end if you want it. Change C9 to 33nF and insert a 5k pot in series between C9 and ground.