Wurlitzer 44 Tube vibrato clone stompbox

[RGP]

  I've been working on this for a while.

[RGP]

  This is a true pitch shifting vibrato that Richard Dorf highly praised. I tried the circuit as shown, the ouput was weak and distorted, but it did work. I'm thinking it needs a higher plate voltage and considering cloning the Paia tube head's design to accomplish that. I'm also thinking about adding an op amp on the output to bring the impedance down to 1K or less. Any suggestions on improving this circuit?   

[Ben N]

Do you have the rest of the organ schematic? Where does the output of this circuit go there? And what did Wurlitzer feed into the plates of the 12au7s? That info may address your issues.

[duck_arse]

in your circuit diagram, the first cap in the output string is shown connected hard-to the supply. nothing much to hear there. I can barely read the values on that circuit.

[RGP]

  Actually this my attempt of cloning the Wurlitzer 44 vibrato for a stompbox. In the organ the tubes are 6sl7's & 6sn7's running at 250-260 volts on the plates. I replaced the tube based LFO with an opamp type & added the phase splitter.  I also added the HP & LP filters from the Fender Harmonic Virbrato (actually that's a tremolo) to somewhat simulate a Leslie cabinet. The output filter was designed by the late Roly Roper to minimize LFO thumping. At 12 volts it modualates, but the ouput is very weak and distorted.
  I'm looking at the tube head as a means to increase the plate voltage. I'm sorry the image isn't as clear as it should be. Maybe I need to use a different graphics file type to clear it up. The original schematic is a rather large file, probably too large to attach here. I can cut it into sections if that woud help. If you look at the VOX AC with vibrato it's also a clone of the Wurlitzer 44 circuit. Sluckey made a great clone of that amp. He may hvae posted it here too.             

[duck_arse]

I can hardly even see that image, but you know it well enough. note the resistor top left corner.



and this is a vox something. note well resistor R22, which allows the power supply to remain unmodulated, keeping all other stages happy, while also allowing the phase modulator valve to do some modulating of the signal, and feeding that to the filter and amplifier.

can you show the original circuit you are translating, please?

[RGP]

Duck. Thanks for pointing out the error on my schematic. I'll make the proper corrections on the next draft. the way I drew it is wrong compared to the circuit I built. The schematic you posted is the Wurlitzer 44 vibrato's modulating section I'm trying to clone to operate at a lower plate voltage. The tube based lfo for the vibrato is too fast for my taste.
What I intend to do is use a wah pedal rack & pinion to vary the lfo's speed for ramping up or down, to simulate a Leslie cabinet used that way. Think Frampton's use of that trick, for example. Will this circuit truly sound like a Leslie cabinet? Absolutely not! But, it would be a great vibrato with some additional features that I mentioned earlier.         

[RGP]

I've revised the schematic, made several changes, added sections of the PaIA tube mic's circuit to increase the plate voltage & added it's mic's output section to lower the output impedance. I also made some changes to the LFO that I feel would make it a bit better. This is only a concept drawing, it hasn't been built or tested yet.  Any suggestions wil be greatly appreciated.       

[RGP]

I'm considering the tube mic's power supply for this. I don't fully understand how this works. Is there something missing in that schematic? How does the 4049 increase the voltage without the VCC being connected to it? Will someone kindly explain this to me?

[PRR]

....I don't fully understand how this works. Is there something missing in that schematic? How does the 4049 increase the voltage without the VCC being connected to it?

[RGP]

PRR. Thanks for clearing that up for me. Could that supply enough power for a pair of 12au7's?     

[RGP]

This is revision 2 that adds a tremelo/vibrato selector switch found on 1960's era Vox AC 15 & 30 Amps containing the Jennings circuit which is a clone of the Wurlizter 44 vibrato. There's a funny story behind how that came to be thanks to a screwdriver For a great clone of those Vox amps check out Steve Lucky's site. As for my clone of the vibrato its still only a concept. I'm working out the rest thanks to the advice I'm getting from here. When the circuit is finished  I'll be housing it in a Line 6 floorboard unit that has a rocker pedal (to control the speed) and 4 switches. 1 switch will be sed for true bypass and another for tremolo/vibrato select.