12AU7 tremelo

[Mick Bailey]

I've just started designing a simple 12AU7 tube trem (no solid state) and thought "this must have been done to death" but initial searches haven't turned up anything.

Does anyone know of such a design, and more importantly, is anyone interested?

[Renegadrian]

It's a couple of months that I want to work on one, but never managed to find enough free time...
Now I have some more, having lost my last job, so I believe I can work on that soon...Let's see what will be our results.
I will be happy to experiment...

[birt]

i would start looking at something like this: http://www.schematicheaven.com/fenderamps/champ_vibro_aa764_schem.pdf

[frequencycentral]

If you mean using a 12AU7 as a phase shift oscillator at high voltage, there's a design over at AX84 that Rick Campbell posted. If you mean low voltage there's this one:

http://www.diystompboxes.com/smfforum/index.php?topic=70160.0


EDIT: Here's Rick Campbell's design, 12AX7 though: http://ricktone.rickcampbell.org/cgi-bin/getimg.cgi/Schematic_TremODrive_1.pdf

[Mick Bailey]

Probably closer to the TremODrive having now seen the schematic, but a 12v version (sorry, I should have mentioned the 12v intention). I wanted to do a single tube design without solid state as I've already built a few op/amp and transistor trems. I've already got the schematic together ready to breadboard so will crack on and see what comes out. The reason for my original post was to find out if this type of design had already done the rounds and was pointless in developing something that others had already achieved.

The HV designs work very well, but the voltages can deter many so I thought I'd put something out that anyone could build without concerns. The broad idea is an oscillator built around half of a 12AU7 and the other half as an amplifier with a cathode wiggle.

Seems promising at the moment, but we live in hope and die in despair.............

[frequencycentral]

I don't think you can get a 12AU7 to be a phase shift oscillator without high voltage. I've tried and failed at ~80 volts. Even at high voltage it may not have enough gain. Though you could try a tapered phase shift oscillator: http://www.freewebs.com/valvewizard2/TaperedPhaseShiftOscillators.pdf

[Mick Bailey]

You're right - looking at this idea again and the info you've supplied, there wouldn't be enough gain. The tapered phase shift approach looks like it could be made to work due to the better loading characteristics of the network. I guess the only way to find out would be to experiment with values and see whether a usable frequency range is possible. I need to study the maths in a bit more depth to get a better angle on this.

[g.]

EDIT: Here's Rick Campbell's design, 12AX7 though: http://ricktone.rickcampbell.org/cgi-bin/getimg.cgi/Schematic_TremODrive_1.pdf

didn't know that link !

cool project
thanks

[kristoffereide]

I can't see how he draws 210V from a 120V transformer....

[Renegadrian]

I can't see how he draws 210V from a 120V transformer....

A quite simple voltage doubler, with caps and diodes.

[kristoffereide]

aaah, didn't notice that thanks

[Mick Bailey]

Just an update on the tapered phase-shift oscillator - I couldn't get it to oscillate at 12v. The scope doesn't even show an initial oscillation. I've substituted components and it seems that getting any kind of a sine wave out of this will be the challenge. I'm not defeated though, and all ideas are welcome.

[frequencycentral]

I tried the tapered PSO a while back with a 12AU7 and my MAX charge pump at ~80 volts with no luck. Maybe it would work with a 12AX7? From experiments I've done with 6112 subminis (similar spec to 12AX7), they have less gain than 6111 (similar to 12AU7) at low voltage. There may be a point at which a 12AX7/6112 will work as a tapered PSO without HT, using a 'safe' charge pump to get your B+. Not pure low voltage, but not dealing with dangerous voltages that would put people off. The only 12AX7 I have is in my VJ, but I have a couple of 6112, if I get a chance I'll try this idea out - if it works with a 6112 I'll pull the 12AX7 from my VJ and try it with that. Not this weekend though, I have a phaser to debug!

[earthtonesaudio]

Well, you could always go the "more tubes" route and use both halves in mu-amp configuration for your oscillator.

[doitle]

While we are on the subject of tremolos. Could a tremolo be created using a switch? Doing something like using an analog switch and a 555 timer to trigger it. Run the guitar signal through the switch and then also run the guitar signal around the switch and use a mixing configuration to mix the switched and dry signals to adjust the depth of your tremolo. The rate would be controlled by the 555.

I think I might try to bread board something like this up this weekend since I'm stuck with no car and no room mates.

[Mick Bailey]

As the output from the switch would be chopped It wouldn't sound like a tremolo, even when mixed back with the dry signal. It would make for an interesting chopper pedal for Tom Morello type effects with just the switch output.