How to add Tremulus Lune "Ramp Up" mod to an EA Tremolo??

[davidjnichols]

I have an EA Tremolo and I'd like to add the Tremulus Lune "Ramp Up" mod to it to get a different wave form.  I would toggle between the regular EA Trem sine wave and the "Ramp Up" sawtooth wave via DPDT.  I know it's gotta be possible.  I just have no idea where in the circuit to put it.  

http://www.commonsound.com/kits/doku.php?id=commonsound:tremulus
http://commonsound.org/tremulus/tremmods.pdf
http://fuzzcentral.ssguitar.com/tremulus.php

[darron]

they both use different oscillators.

here's a link to a good EA trem schematic:

http://www.tonepad.com/getFileInfo.asp?id=130

hopefully someone has a simple solution to do it and ramp it smoothly.

[midwayfair]

You can still use a diode across the speed pot, but it's not as good as in the Lune. I made one for a friend with a pot instead of the switch, but the switch will work much better than the pot did. I'm not really certain which way the diode has to face, so you might need to experiment.

You actually end up with something a little more lopsided, more like a lope than a saw-tooth wave. Also, it affects the speed some (speeds up some as I recall) and the hardness of the wave. Make sure whatever you do that it's reversable until you're sure you like it.

EDIT: you only need a SPDT, by the way. You're just switching out the diode.

1
2
3

1: Speed pot 2
2: Diode side A
3: Speed pot 3 and diode side B
Flipped one way, nothing is connected. Flipped the other way, Speed 3 is connected to speed 2 through a diode.

Or use a SPST and just put the diode in series with one of the wires back to the speed pot.

[duck_arse]

I rekon the easiest(?) way to do would be swap the oscillator for a dual op-amp type, but I've got the pso on my breadboard front and centre, so I'll have a dash at diode ramps tomorrow.

(perhaps increase the resistor in the non-pot leg, and do the diode across that, one way or the other)

[Plexi]

You can still use a diode across the speed pot, but it's not as good as in the Lune. I made one for a friend with a pot instead of the switch, but the switch will work much better than the pot did. I'm not really certain which way the diode has to face, so you might need to experiment.

You actually end up with something a little more lopsided, more like a lope than a saw-tooth wave. Also, it affects the speed some (speeds up some as I recall) and the hardness of the wave. Make sure whatever you do that it's reversable until you're sure you like it.

EDIT: you only need a SPDT, by the way. You're just switching out the diode.

1
2
3

1: Speed pot 2
2: Diode side A
3: Speed pot 3 and diode side B
Flipped one way, nothing is connected. Flipped the other way, Speed 3 is connected to speed 2 through a diode.

Or use a SPST and just put the diode in series with one of the wires back to the speed pot.

There's any schematic of this?

Thanks!

[Transmogrifox]

You actually end up with something a little more lopsided, more like a lope than a saw-tooth wave. Also, it affects the speed some (speeds up some as I recall)

Yes this would speed it up.  This by far sounds like the most simple option I can imagine -- kudos Jon

Note to the OP if you do want to go as far as adding a second oscillator to the EA tremolo, you just disconnect the 0.47 uF cap from the Q3 collector (reference tonepad schematic and connect that to the output of the oscillator used in the Tremulus Lune (4558D U2 Pin 1).  Either hardwire the mod and switch back and forth between the EA oscillator and the ramp, or just use the Tremulus Oscillator and use the ramp mod to switch modes.  My guess is the Tremulus oscillator could be a nice addition to the EA....but then, why not just build a Tremulus Lune for all of that added complexity...

...which brings us back to the idea Jon posted

[midwayfair]

Wait wait!!!!! Ignore years ago me. I haven't retested that recently but I think it didn't actually work properly (and yes I say this after I built a pedal using the method described). You can definitely change the duty cycle with the collector resistor, and I think you can do something with diodes but I'm not sure where off the top of my head. But the speed pot idea was wrong. You're looking for a spot where you can use the diodes to pass only one side of the wave, maybe the feedback loop of the transistor. It cant's be after it's decoupled though.

[Transmogrifox]

Wait wait!!!!!

I simulated this and it "works" in the sense that the waveform becomes asymmetric, but you are correct it doesn't exactly give you a ramp.  I messed with some other things in simulation and nothing really gets you there without turning it into set/reset circuit (relaxation oscillator) which is not a simple matter of adding a switch and diode to the existing circuit.  Probably Jon's diode hack is the closest you can get to something that at least changes LFO shape in some meaningful way even though maybe not what was envisioned.

[kaycee]

Use a DPDT switch and add a second speed pot. A momentary footswitch is a good candidate. When the switch is pressed the rate goes to the setting of the second pot while held and returns to first when released. You get a ramping effect if the difference between the two is enough, you can't control the speed of that transition though.