Tycobrahe octavia vs. Bobtavia

[mojo321]

Hi all, I know the Bobtavia isn't shown on this board, but you can find it if you google.

The Bobtavia uses LM386 to replace the transistor circuits of the tychobrahe, more or less.  After all of that business, the two become practically identical: input into the transformer.  

My question is, why does the Tychobrahe have the center pin of the primary going to ground, whereas the Bobtavia has the same pin going to a 100k resistor from +9V?  I have studied this for a while.  I'm fairly certain I am comparing apples to apples here.  So when I pulled the second pin on my completed Tychobrahe off of the ground, and attached it to a 100k , and fed it 9V, I was surprised to hear the thing go psycho on me.  It just started making a loud vibrating hum, with no signal discernible from the guitar.  Fail.   But WHY?  Everything upstream of the transformer is simply a difference in tone and fuzz, right?  

[induction]

I don't know what happened in your case, but it seems like it should work the same.

I've breadboarded the Neoctavia (based on the Bobtavia but uses op-amps instead of the 386) and tried it both ways. Center tap through 100k to 9V gave a better octave for me. Center tap to ground gave a louder signal, but it was louder because it had more fundamental in it. It seemed to have a little less crossover distortion as well.

I breadboarded the Bobtavia as well, but found it to be less reliable. Sometimes it just gave me a hum, probably similar to the one you described.