Negative Ground Octavia?

[petemoore]

Anyone try a negative ground Tychobrahe Octavia?
 I have one perfed with reverse polarity on the Electro caps, I'm thinking I can simply NpN the PNP's and vice versa...but wondering if there are other considerations I should be thinking about or that would prevent it from working properly. [?].

[B Tremblay]

I've built the one from GGG, which is negative-ground.  You're correct, the only necessary change from the positive-ground version is reversing the polarity of all the electros.  Diode and transformer orientation remain the same.

[petemoore]

Thanks B.
 I've got some 'thumb' signal coming through, [guitars upstairs],...
 Ever try a Ge Darlington? I have many Ge transistors around, probably up to 180hfe for the highest one...should the 'second transistro of a darlington pair be the highest hfe of the two?

[B Tremblay]

I don't recall ever having tried a Ge darlington.  I do remember trying a Ge in Q1, but I don't know the results because I didn't write any notes about it.

I assume that the results weren't significant.  For what it's worth, there have been only three circuits that I ended up liking a PNP Ge transistor better than a generic Si PNP:

Purple Peaker (Q1)
Green Ringer (Q2, also used Ge diodes)
Harmonic Jerkulator (Q1)

[petemoore]

I just switched it to positive ground.
 Getting faint octave...of course I'm temporarily using two Si's per where there'd be one Ge. Seems to be basically Octaviating...needs a little more attention.
 I think it may be important to match the clipping threshold of the Ge' diodes when I get them, so I probably will.

[phillip]

I've built a few negative ground Tycos and they sound exactly the same as the positive ground.

All you need to do is replace the NPN Q1 with a PNP...I used 2N5087.  Then replace the PNP Q2 & Q3 with NPN...I used 2N4401.  Then reverse the electro. capacitors and you're done.  You don't need to reverse the two diodes on the output.

Phillip

[bwanasonic]

I built the GGG Neg ground version (perf). I do get a bit of whistling squeal if I crank the fuzz knob all the way*, but I rarely use it with the fuzz turned above fully counter-clockwise (for maximum octave effect). I did just fool with the part values, and ended up with a Ge in Q1, but it was not a huge difference. I  also like a 1uf film for the input cap. A power supply is advised from what I remember, as the thing eats batteries.


Kerry M

*most likely from sloppy lead dress on my part.