Hot Harmonics/49'er type overdrive problem -- octave overtone...

[mordechai]

I just put together a device similar to the Hot Harmonics or Mark Hammer's 49'er...it's basically a Fetzer Valve type Jfet boost going into a modified Red Llama.  The sound on chords and mid-fretboard solos is really nice and natural.  But when I go for any notes above the 12th fret, I hear a distinct octave-up overtone.  I've toyed with the ratio of boost stage gain vs. 4049 stage gain, and I can tone it down a bit by bumping up the latter and bringing down the former, but it doesn't fully go away.  I've also tried biasing the Jfet differently (4.5 volts vs. 5.5 volts and even up to 6 volts) for different harmonic characteristic, but it doesn't cut that upper octave ghost tone out of those notes.  Any suggestions on how I can quiet that octave overtone down?

[anotherjim]

Are the 4049 stages fitted with pull-down resistors on inputs ? That would cause asymmetric clipping at top which might cause the second harmonic.  On top of all that, the 4049U output isn't symmetrical having a lower output impedance when driving low than driving high. Driving the chip harder with your JFET input stage may be exaggerating this. The 4069U is somewhat cleaner in this regard.
Size of coupling capacitors you have might be the reason it happens most on the high notes.
Please post a schematic, or we're guessing!

[mordechai]

Actually, I realized the problem wasn't the circuit -- it was my amp!  I have a Fender Hot Rod Deluxe and I am pretty sure one or some of the tubes are failing and need to be replaced.  I plugged into the amp directly, turned up the gain, and the octave ghost tone was there.  The 4049 circuit makes it a little more pronounced, but I don't think the problem is in the circuit...I plugged my guitar into a different overdrive and the pronounced octave ghost note was there too.  So the issue really does seem to be the amp, and any stronger/hot overdrive signal just makes it jump out more.

[Mark Hammer]

Are you sure you didn't press the "Hazerai" button on the footswitch? 

(Note: While many might be most familiar with the Hazerai button on the EHX Memory Man, the original yiddish term - referring to the sorts of leftovers and third tier foodstuffs one would feed pigs - is generally used in a pejorative sense, as in "hazerai" = crap)

[GibsonGM]

Actually, I realized the problem wasn't the circuit -- it was my amp!  I have a Fender Hot Rod Deluxe and I am pretty sure one or some of the tubes are failing and need to be replaced.  I plugged into the amp directly, turned up the gain, and the octave ghost tone was there.  The 4049 circuit makes it a little more pronounced, but I don't think the problem is in the circuit...I plugged my guitar into a different overdrive and the pronounced octave ghost note was there too.  So the issue really does seem to be the amp, and any stronger/hot overdrive signal just makes it jump out more.

You can try swapping the 12AX7 preamp tubes around, see if that changes the 'ghost notes'...tapping on them GENTLY a bit w/ a pencil eraser can also reveal microphonics.   I have a HRDx also, this isn't an unheard of issue...

[mordechai]

Are you sure you didn't press the "Hazerai" button on the footswitch? 

(Note: While many might be most familiar with the Hazerai button on the EHX Memory Man, the original yiddish term - referring to the sorts of leftovers and third tier foodstuffs one would feed pigs - is generally used in a pejorative sense, as in "hazerai" = crap)

Hazerai more or less describes any circuit I've ever built.   :-)