pitch-shifting tube vibrato unit

[tubeswell]

Saw a similar thing (over at the Hoffman forum) one a few months back and liked the sounds of that so I decided to build one for myself. Its a stand-alone vibrato unit (like a stand alone reverb unit, but for vibrato), only its pitch-shifting vibrato, so its not just another trem unit.

This unit uses a saturable reactor from a hammond organ, which is a kind of triple transformer array with one side of each of the three transformers wired in series with the other two and fed by an oscillator. The other sides of the transformers are utilised in feedback loops from the 12AU7 triodes. There are 4 sigma (phase shift/pitch/harmonic) controls (one for each 12AU7 triode), a feedback control, an output/bypass mixing control and the LFO controls. The unit is driven by 2 x 12AU7, 2 x 12AX7 and a 12DW7. There is a CF bypass so you can run the unit un-effected by turning down the output level control, which is wired with a dual gang pot that also serves and the 'dry' mix control when turned down. Schematic here:

The Amp Garage ::

I was a bit concerned about how many parts I was cramming in there, but it didn't affect the sound.

Found a nice bit of scandinavian pine in an old drawer end at the local tip, which cleaned up nicely for the front of the box.

Only delved into the tip of sounds so far but got several variations ranging from chorus to phase to vibrato to tremolo by tweaking the 4 'sigma' controls, and many variations in between. There are a few settings that sound quite magnatone-ish with my strat.

Soundbyte links (running the unit into my BFPR clone - not a great recording because just stratight into garbageband on my mac with the internal mic. I will try and find some time over the break to set down a jazzier bit of sound with it properly mic'd thru my desk etc):

http://www.nzguitars.com/forum/downl...le.php?id=9003

http://www.nzguitars.com/forum/downl...le.php?id=9002